Add support for the function `name` property.

This resolves #78.

Merged remote-tracking branch 'janek/js_function_name_1'

61 files changed, 1033 insertions, 184 deletions

diff --git a/js/src/builtin/ModuleObject.cpp b/js/src/builtin/ModuleObject.cpp
index 3bfc8f60b..40fd008b9 100644
--- a/js/src/builtin/ModuleObject.cpp
+++ b/js/src/builtin/ModuleObject.cpp
@@ -1205,7 +1205,7 @@ ModuleBuilder::processExport(frontend::ParseNode* pn)
       case PNK_FUNCTION: {
           RootedFunction func(cx_, kid->pn_funbox->function());
           if (!func->isArrow()) {
-              RootedAtom localName(cx_, func->name());
+              RootedAtom localName(cx_, func->explicitName());
               RootedAtom exportName(cx_, isDefault ? cx_->names().default_ : localName.get());
               MOZ_ASSERT_IF(isDefault, localName);
               if (!appendExportEntry(exportName, localName))
diff --git a/js/src/builtin/ReflectParse.cpp b/js/src/builtin/ReflectParse.cpp
index 748ff7351..eef6fd7ec 100644
--- a/js/src/builtin/ReflectParse.cpp
+++ b/js/src/builtin/ReflectParse.cpp
@@ -3415,7 +3415,7 @@ ASTSerializer::function(ParseNode* pn, ASTType type, MutableHandleValue dst)
 #endif
 
     RootedValue id(cx);
-    RootedAtom funcAtom(cx, func->name());
+    RootedAtom funcAtom(cx, func->explicitName());
     if (!optIdentifier(funcAtom, nullptr, &id))
         return false;
 
@@ -3423,7 +3423,7 @@ ASTSerializer::function(ParseNode* pn, ASTType type, MutableHandleValue dst)
     NodeVector defaults(cx);
 
     RootedValue body(cx), rest(cx);
-    if (func->hasRest())
+    if (pn->pn_funbox->hasRest())
         rest.setUndefined();
     else
         rest.setNull();
diff --git a/js/src/builtin/TypedObject.cpp b/js/src/builtin/TypedObject.cpp
index b7297c894..ae74f01bf 100644
--- a/js/src/builtin/TypedObject.cpp
+++ b/js/src/builtin/TypedObject.cpp
@@ -230,7 +230,7 @@ const Class js::ScalarTypeDescr::class_ = {
 
 const JSFunctionSpec js::ScalarTypeDescr::typeObjectMethods[] = {
     JS_SELF_HOSTED_FN("toSource", "DescrToSource", 0, 0),
-    JS_SELF_HOSTED_FN("array", "ArrayShorthand", 1, JSFUN_HAS_REST),
+    JS_SELF_HOSTED_FN("array", "ArrayShorthand", 1, 0),
     JS_SELF_HOSTED_FN("equivalent", "TypeDescrEquivalent", 1, 0),
     JS_FS_END
 };
diff --git a/js/src/frontend/BytecodeCompiler.cpp b/js/src/frontend/BytecodeCompiler.cpp
index 3fbfdaa1a..76afe80b1 100644
--- a/js/src/frontend/BytecodeCompiler.cpp
+++ b/js/src/frontend/BytecodeCompiler.cpp
@@ -336,10 +336,10 @@ BytecodeCompiler::compileScript(HandleObject environment, SharedContext* sc)
                 if (!deoptimizeArgumentsInEnclosingScripts(cx->asJSContext(), environment))
                     return nullptr;
             }
-            if (!NameFunctions(cx, pn))
-                return nullptr;
             if (!emitter->emitScript(pn))
                 return nullptr;
+            if (!NameFunctions(cx, pn))
+                return nullptr;
             parser->handler.freeTree(pn);
 
             break;
@@ -397,15 +397,15 @@ BytecodeCompiler::compileModule()
     if (!pn)
         return nullptr;
 
-    if (!NameFunctions(cx, pn))
-        return nullptr;
-
     Maybe<BytecodeEmitter> emitter;
     if (!emplaceEmitter(emitter, &modulesc))
         return nullptr;
     if (!emitter->emitScript(pn->pn_body))
         return nullptr;
 
+    if (!NameFunctions(cx, pn))
+        return nullptr;
+
     parser->handler.freeTree(pn);
 
     if (!builder.initModule())
@@ -453,9 +453,6 @@ BytecodeCompiler::compileStandaloneFunction(MutableHandleFunction fun,
             return false;
     } while (!fn);
 
-    if (!NameFunctions(cx, fn))
-        return false;
-
     if (fn->pn_funbox->function()->isInterpreted()) {
         MOZ_ASSERT(fun == fn->pn_funbox->function());
 
@@ -472,6 +469,9 @@ BytecodeCompiler::compileStandaloneFunction(MutableHandleFunction fun,
         MOZ_ASSERT(IsAsmJSModule(fun));
     }
 
+    if (!NameFunctions(cx, fn))
+        return false;
+
     if (!maybeCompleteCompressSource())
         return false;
 
@@ -646,9 +646,6 @@ frontend::CompileLazyFunction(JSContext* cx, Handle<LazyScript*> lazy, const cha
     if (!pn)
         return false;
 
-    if (!NameFunctions(cx, pn))
-        return false;
-
     RootedScriptSource sourceObject(cx, lazy->sourceObject());
     MOZ_ASSERT(sourceObject);
 
@@ -667,7 +664,13 @@ frontend::CompileLazyFunction(JSContext* cx, Handle<LazyScript*> lazy, const cha
     if (!bce.init())
         return false;
 
-    return bce.emitFunctionScript(pn->pn_body);
+    if (!bce.emitFunctionScript(pn->pn_body))
+        return false;
+
+    if (!NameFunctions(cx, pn))
+        return false;
+
+    return true;
 }
 
 bool
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index 1e9d8f224..acf734794 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -1053,7 +1053,7 @@ BytecodeEmitter::EmitterScope::enterFunction(BytecodeEmitter* bce, FunctionBox*
             if (p) {
                 MOZ_ASSERT(bi.kind() == BindingKind::FormalParameter);
                 MOZ_ASSERT(!funbox->hasDestructuringArgs);
-                MOZ_ASSERT(!funbox->function()->hasRest());
+                MOZ_ASSERT(!funbox->hasRest());
                 p->value() = loc;
                 continue;
             }
@@ -4070,7 +4070,7 @@ BytecodeEmitter::isRunOnceLambda()
     FunctionBox* funbox = sc->asFunctionBox();
     return !funbox->argumentsHasLocalBinding() &&
            !funbox->isGenerator() &&
-           !funbox->function()->name();
+           !funbox->function()->explicitName();
 }
 
 bool
@@ -4463,7 +4463,7 @@ BytecodeEmitter::emitDestructuringLHS(ParseNode* target, DestructuringFlavor fla
 }
 
 bool
-BytecodeEmitter::emitConditionallyExecutedDestructuringLHS(ParseNode* target, DestructuringFlavor flav)
+BytecodeEmitter::emitDestructuringLHSInBranch(ParseNode* target, DestructuringFlavor flav)
 {
     TDZCheckCache tdzCache(this);
     return emitDestructuringLHS(target, flav);
@@ -4491,7 +4491,7 @@ BytecodeEmitter::emitIteratorNext(ParseNode* pn, bool allowSelfHosted)
 }
 
 bool
-BytecodeEmitter::emitDefault(ParseNode* defaultExpr)
+BytecodeEmitter::emitDefault(ParseNode* defaultExpr, ParseNode* pattern)
 {
     if (!emit1(JSOP_DUP))                                 // VALUE VALUE
         return false;
@@ -4507,13 +4507,77 @@ BytecodeEmitter::emitDefault(ParseNode* defaultExpr)
         return false;
     if (!emit1(JSOP_POP))                                 // .
         return false;
-    if (!emitConditionallyExecutedTree(defaultExpr))      // DEFAULTVALUE
+    if (!emitInitializerInBranch(defaultExpr, pattern))   // DEFAULTVALUE
         return false;
     if (!emitJumpTargetAndPatch(jump))
         return false;
     return true;
 }
 
+bool
+BytecodeEmitter::setOrEmitSetFunName(ParseNode* maybeFun, HandleAtom name,
+                                     FunctionPrefixKind prefixKind)
+{
+    if (maybeFun->isKind(PNK_FUNCTION)) {
+        // Function doesn't have 'name' property at this point.
+        // Set function's name at compile time.
+        RootedFunction fun(cx, maybeFun->pn_funbox->function());
+
+        // Single node can be emitted multiple times if it appears in
+        // array destructuring default.  If function already has a name,
+        // just return.
+        if (fun->hasCompileTimeName()) {
+#ifdef DEBUG
+            RootedAtom funName(cx, NameToFunctionName(cx, name, prefixKind));
+            if (!funName)
+                return false;
+            MOZ_ASSERT(funName == maybeFun->pn_funbox->function()->compileTimeName());
+#endif
+            return true;
+        }
+
+        RootedAtom funName(cx, NameToFunctionName(cx, name, prefixKind));
+        if (!funName)
+            return false;
+        fun->setCompileTimeName(name);
+        return true;
+    }
+
+    uint32_t nameIndex;
+    if (!makeAtomIndex(name, &nameIndex))
+        return false;
+    if (!emitIndexOp(JSOP_STRING, nameIndex))   // FUN NAME
+        return false;
+    uint8_t kind = uint8_t(prefixKind);
+    if (!emit2(JSOP_SETFUNNAME, kind))          // FUN
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitInitializer(ParseNode* initializer, ParseNode* pattern)
+{
+    if (!emitTree(initializer))
+        return false;
+
+    if (!pattern->isInParens() && pattern->isKind(PNK_NAME) &&
+        initializer->isDirectRHSAnonFunction())
+    {
+        RootedAtom name(cx, pattern->name());
+        if (!setOrEmitSetFunName(initializer, name, FunctionPrefixKind::None))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitInitializerInBranch(ParseNode* initializer, ParseNode* pattern)
+{
+    TDZCheckCache tdzCache(this);
+    return emitInitializer(initializer, pattern);
+}
+
 class MOZ_STACK_CLASS IfThenElseEmitter
 {
     BytecodeEmitter* bce_;
@@ -4765,7 +4829,7 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
                     return false;
                 if (!emitUint32Operand(JSOP_NEWARRAY, 0))         // ... OBJ? ARRAY
                     return false;
-                if (!emitConditionallyExecutedDestructuringLHS(member, flav)) // ... OBJ?
+                if (!emitDestructuringLHSInBranch(member, flav))  // ... OBJ?
                     return false;
 
                 if (!ifThenElse.emitElse())                       // ... OBJ? ITER
@@ -4782,7 +4846,7 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
                 return false;
             if (!emit1(JSOP_POP))                                 // ... OBJ? ARRAY
                 return false;
-            if (!emitConditionallyExecutedDestructuringLHS(member, flav)) // ... OBJ?
+            if (!emitDestructuringLHSInBranch(member, flav))      // ... OBJ?
                 return false;
 
             if (!isHead) {
@@ -4834,7 +4898,7 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
         if (pndefault) {
             // Emit only pndefault tree here, as undefined check in emitDefault
             // should always be true.
-            if (!emitConditionallyExecutedTree(pndefault))        // ... OBJ? ITER VALUE
+            if (!emitInitializerInBranch(pndefault, subpattern))  // ... OBJ? ITER VALUE
                 return false;
         } else {
             if (!isElision) {
@@ -4845,7 +4909,7 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
             }
         }
         if (!isElision) {
-            if (!emitConditionallyExecutedDestructuringLHS(subpattern, flav)) // ... OBJ? ITER
+            if (!emitDestructuringLHSInBranch(subpattern, flav))  // ... OBJ? ITER
                 return false;
         } else if (pndefault) {
             if (!emit1(JSOP_POP))                                 // ... OBJ? ITER
@@ -4872,12 +4936,12 @@ BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlav
             return false;
 
         if (pndefault) {
-            if (!emitDefault(pndefault))                          // ... OBJ? ITER VALUE
+            if (!emitDefault(pndefault, subpattern))              // ... OBJ? ITER VALUE
                 return false;
         }
 
         if (!isElision) {
-            if (!emitConditionallyExecutedDestructuringLHS(subpattern, flav)) // ... OBJ? ITER
+            if (!emitDestructuringLHSInBranch(subpattern, flav))  // ... OBJ? ITER
                 return false;
         } else {
             if (!emit1(JSOP_POP))                                 // ... OBJ? ITER
@@ -4980,7 +5044,7 @@ BytecodeEmitter::emitDestructuringOpsObject(ParseNode* pattern, DestructuringFla
             return false;
 
         if (subpattern->isKind(PNK_ASSIGN)) {
-            if (!emitDefault(subpattern->pn_right))
+            if (!emitDefault(subpattern->pn_right, subpattern->pn_left))
                 return false;
             subpattern = subpattern->pn_left;
         }
@@ -5094,7 +5158,7 @@ BytecodeEmitter::emitSingleDeclaration(ParseNode* declList, ParseNode* decl,
     if (!initializer && declList->isKind(PNK_VAR))
         return true;
 
-    auto emitRhs = [initializer, declList](BytecodeEmitter* bce, const NameLocation&, bool) {
+    auto emitRhs = [initializer, declList, decl](BytecodeEmitter* bce, const NameLocation&, bool) {
         if (!initializer) {
             // Lexical declarations are initialized to undefined without an
             // initializer.
@@ -5105,7 +5169,7 @@ BytecodeEmitter::emitSingleDeclaration(ParseNode* declList, ParseNode* decl,
         }
 
         MOZ_ASSERT(initializer);
-        return bce->emitTree(initializer);
+        return bce->emitInitializer(initializer, decl);
     };
 
     if (!emitInitializeName(decl, emitRhs))
@@ -5164,6 +5228,12 @@ BytecodeEmitter::emitAssignment(ParseNode* lhs, JSOp op, ParseNode* rhs)
             if (!EmitAssignmentRhs(bce, rhs, emittedBindOp ? 2 : 1))
                 return false;
 
+            if (!lhs->isInParens() && op == JSOP_NOP && rhs && rhs->isDirectRHSAnonFunction()) {
+                RootedAtom name(bce->cx, lhs->name());
+                if (!bce->setOrEmitSetFunName(rhs, name, FunctionPrefixKind::None))
+                    return false;
+            }
+
             // Emit the compound assignment op if there is one.
             if (op != JSOP_NOP && !bce->emit1(op))
                 return false;
@@ -5788,7 +5858,7 @@ BytecodeEmitter::emitIf(ParseNode* pn)
 
   if_again:
     /* Emit code for the condition before pushing stmtInfo. */
-    if (!emitConditionallyExecutedTree(pn->pn_kid1))
+    if (!emitTreeInBranch(pn->pn_kid1))
         return false;
 
     ParseNode* elseNode = pn->pn_kid3;
@@ -5801,7 +5871,7 @@ BytecodeEmitter::emitIf(ParseNode* pn)
     }
 
     /* Emit code for the then part. */
-    if (!emitConditionallyExecutedTree(pn->pn_kid2))
+    if (!emitTreeInBranch(pn->pn_kid2))
         return false;
 
     if (elseNode) {
@@ -5814,7 +5884,7 @@ BytecodeEmitter::emitIf(ParseNode* pn)
         }
 
         /* Emit code for the else part. */
-        if (!emitConditionallyExecutedTree(elseNode))
+        if (!emitTreeInBranch(elseNode))
             return false;
     }
 
@@ -6283,8 +6353,8 @@ BytecodeEmitter::emitForIn(ParseNode* forInLoop, EmitterScope* headLexicalEmitte
                 if (!updateSourceCoordNotes(decl->pn_pos.begin))
                     return false;
 
-                auto emitRhs = [initializer](BytecodeEmitter* bce, const NameLocation&, bool) {
-                    return bce->emitTree(initializer);
+                auto emitRhs = [decl, initializer](BytecodeEmitter* bce, const NameLocation&, bool) {
+                    return bce->emitInitializer(initializer, decl);
                 };
 
                 if (!emitInitializeName(decl, emitRhs))
@@ -6504,7 +6574,7 @@ BytecodeEmitter::emitCStyleFor(ParseNode* pn, EmitterScope* headLexicalEmitterSc
     if (jmp.offset == -1 && !emitLoopEntry(forBody, jmp))
         return false;
 
-    if (!emitConditionallyExecutedTree(forBody))
+    if (!emitTreeInBranch(forBody))
         return false;
 
     // Set loop and enclosing "update" offsets, for continue.  Note that we
@@ -6903,7 +6973,7 @@ BytecodeEmitter::emitFunction(ParseNode* pn, bool needsProto)
 {
     FunctionBox* funbox = pn->pn_funbox;
     RootedFunction fun(cx, funbox->function());
-    RootedAtom name(cx, fun->name());
+    RootedAtom name(cx, fun->explicitName());
     MOZ_ASSERT_IF(fun->isInterpretedLazy(), fun->lazyScript());
     MOZ_ASSERT_IF(pn->isOp(JSOP_FUNWITHPROTO), needsProto);
 
@@ -7284,7 +7354,7 @@ BytecodeEmitter::emitWhile(ParseNode* pn)
     if (!emitLoopHead(pn->pn_right, &top))
         return false;
 
-    if (!emitConditionallyExecutedTree(pn->pn_right))
+    if (!emitTreeInBranch(pn->pn_right))
         return false;
 
     if (!emitLoopEntry(pn->pn_left, jmp))
@@ -8017,7 +8087,7 @@ BytecodeEmitter::isRestParameter(ParseNode* pn, bool* result)
 
     FunctionBox* funbox = sc->asFunctionBox();
     RootedFunction fun(cx, funbox->function());
-    if (!fun->hasRest()) {
+    if (!funbox->hasRest()) {
         *result = false;
         return true;
     }
@@ -8449,13 +8519,13 @@ BytecodeEmitter::emitConditionalExpression(ConditionalExpression& conditional)
     if (!ifThenElse.emitCond())
         return false;
 
-    if (!emitConditionallyExecutedTree(&conditional.thenExpression()))
+    if (!emitTreeInBranch(&conditional.thenExpression()))
         return false;
 
     if (!ifThenElse.emitElse())
         return false;
 
-    if (!emitConditionallyExecutedTree(&conditional.elseExpression()))
+    if (!emitTreeInBranch(&conditional.elseExpression()))
         return false;
 
     if (!ifThenElse.emitEnd())
@@ -8532,6 +8602,10 @@ BytecodeEmitter::emitPropertyList(ParseNode* pn, MutableHandlePlainObject objp,
                    op == JSOP_INITPROP_GETTER ||
                    op == JSOP_INITPROP_SETTER);
 
+        FunctionPrefixKind prefixKind = op == JSOP_INITPROP_GETTER ? FunctionPrefixKind::Get
+                                        : op == JSOP_INITPROP_SETTER ? FunctionPrefixKind::Set
+                                        : FunctionPrefixKind::None;
+
         if (op == JSOP_INITPROP_GETTER || op == JSOP_INITPROP_SETTER)
             objp.set(nullptr);
 
@@ -8573,6 +8647,12 @@ BytecodeEmitter::emitPropertyList(ParseNode* pn, MutableHandlePlainObject objp,
               case JSOP_INITHIDDENPROP_SETTER:  op = JSOP_INITHIDDENELEM_SETTER; break;
               default: MOZ_CRASH("Invalid op");
             }
+            if (propdef->pn_right->isDirectRHSAnonFunction()) {
+                if (!emitDupAt(1))
+                    return false;
+                if (!emit2(JSOP_SETFUNNAME, uint8_t(prefixKind)))
+                    return false;
+            }
             if (!emit1(op))
                 return false;
         } else {
@@ -8597,6 +8677,11 @@ BytecodeEmitter::emitPropertyList(ParseNode* pn, MutableHandlePlainObject objp,
                     objp.set(nullptr);
             }
 
+            if (propdef->pn_right->isDirectRHSAnonFunction()) {
+                RootedAtom keyName(cx, key->pn_atom);
+                if (!setOrEmitSetFunName(propdef->pn_right, keyName, prefixKind))
+                    return false;
+            }
             if (!emitIndex32(op, index))
                 return false;
         }
@@ -8960,7 +9045,7 @@ BytecodeEmitter::emitFunctionFormalParameters(ParseNode* pn)
     EmitterScope* funScope = innermostEmitterScope;
 
     bool hasParameterExprs = funbox->hasParameterExprs;
-    bool hasRest = funbox->function()->hasRest();
+    bool hasRest = funbox->hasRest();
 
     uint16_t argSlot = 0;
     for (ParseNode* arg = pn->pn_head; arg != funBody; arg = arg->pn_next, argSlot++) {
@@ -9017,7 +9102,7 @@ BytecodeEmitter::emitFunctionFormalParameters(ParseNode* pn)
                 return false;
             if (!emit1(JSOP_POP))
                 return false;
-            if (!emitConditionallyExecutedTree(initializer))
+            if (!emitInitializerInBranch(initializer, bindingElement))
                 return false;
             if (!emitJumpTargetAndPatch(jump))
                 return false;
@@ -9728,7 +9813,7 @@ BytecodeEmitter::emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote)
 }
 
 bool
-BytecodeEmitter::emitConditionallyExecutedTree(ParseNode* pn)
+BytecodeEmitter::emitTreeInBranch(ParseNode* pn)
 {
     // Code that may be conditionally executed always need their own TDZ
     // cache.
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
index 1bb4191ee..9a2ddb568 100644
--- a/js/src/frontend/BytecodeEmitter.h
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -435,7 +435,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     MOZ_MUST_USE bool emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote = EMIT_LINENOTE);
 
     // Emit code for the tree rooted at pn with its own TDZ cache.
-    MOZ_MUST_USE bool emitConditionallyExecutedTree(ParseNode* pn);
+    MOZ_MUST_USE bool emitTreeInBranch(ParseNode* pn);
 
     // Emit global, eval, or module code for tree rooted at body. Always
     // encompasses the entire source.
@@ -648,8 +648,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     // the stack and emits code to destructure a single lhs expression (either a
     // name or a compound []/{} expression).
     MOZ_MUST_USE bool emitDestructuringLHS(ParseNode* target, DestructuringFlavor flav);
-    MOZ_MUST_USE bool emitConditionallyExecutedDestructuringLHS(ParseNode* target,
-                                                                DestructuringFlavor flav);
+    MOZ_MUST_USE bool emitDestructuringLHSInBranch(ParseNode* target, DestructuringFlavor flav);
 
     // emitDestructuringOps assumes the to-be-destructured value has been
     // pushed on the stack and emits code to destructure each part of a [] or
@@ -678,7 +677,16 @@ struct MOZ_STACK_CLASS BytecodeEmitter
 
     // Check if the value on top of the stack is "undefined". If so, replace
     // that value on the stack with the value defined by |defaultExpr|.
-    MOZ_MUST_USE bool emitDefault(ParseNode* defaultExpr);
+    // |pattern| is a lhs node of the default expression.  If it's an
+    // identifier and |defaultExpr| is an anonymous function, |SetFunctionName|
+    // is called at compile time.
+    MOZ_MUST_USE bool emitDefault(ParseNode* defaultExpr, ParseNode* pattern);
+
+    MOZ_MUST_USE bool setOrEmitSetFunName(ParseNode* maybeFun, HandleAtom name,
+                                          FunctionPrefixKind prefixKind);
+
+    MOZ_MUST_USE bool emitInitializer(ParseNode* initializer, ParseNode* pattern);
+    MOZ_MUST_USE bool emitInitializerInBranch(ParseNode* initializer, ParseNode* pattern);
 
     MOZ_MUST_USE bool emitCallSiteObject(ParseNode* pn);
     MOZ_MUST_USE bool emitTemplateString(ParseNode* pn);
diff --git a/js/src/frontend/FullParseHandler.h b/js/src/frontend/FullParseHandler.h
index add881900..0fd137796 100644
--- a/js/src/frontend/FullParseHandler.h
+++ b/js/src/frontend/FullParseHandler.h
@@ -665,6 +665,11 @@ class FullParseHandler
                                                                    ParseNode* pn);
     inline void setLastFunctionFormalParameterDestructuring(ParseNode* funcpn, ParseNode* pn);
 
+    void checkAndSetIsDirectRHSAnonFunction(ParseNode* pn) {
+        if (IsAnonymousFunctionDefinition(pn))
+            pn->setDirectRHSAnonFunction(true);
+    }
+
     ParseNode* newFunctionDefinition() {
         return new_<CodeNode>(PNK_FUNCTION, pos());
     }
@@ -942,6 +947,8 @@ FullParseHandler::setLastFunctionFormalParameterDefault(ParseNode* funcpn, Parse
     if (!pn)
         return false;
 
+    checkAndSetIsDirectRHSAnonFunction(defaultValue);
+
     funcpn->pn_body->pn_pos.end = pn->pn_pos.end;
     ParseNode* pnchild = funcpn->pn_body->pn_head;
     ParseNode* pnlast = funcpn->pn_body->last();
diff --git a/js/src/frontend/ParseNode-inl.h b/js/src/frontend/ParseNode-inl.h
index 395d09b5b..21bd83766 100644
--- a/js/src/frontend/ParseNode-inl.h
+++ b/js/src/frontend/ParseNode-inl.h
@@ -18,7 +18,7 @@ inline PropertyName*
 ParseNode::name() const
 {
     MOZ_ASSERT(isKind(PNK_FUNCTION) || isKind(PNK_NAME));
-    JSAtom* atom = isKind(PNK_FUNCTION) ? pn_funbox->function()->name() : pn_atom;
+    JSAtom* atom = isKind(PNK_FUNCTION) ? pn_funbox->function()->explicitName() : pn_atom;
     return atom->asPropertyName();
 }
 
diff --git a/js/src/frontend/ParseNode.cpp b/js/src/frontend/ParseNode.cpp
index f79baba9e..ece3a45df 100644
--- a/js/src/frontend/ParseNode.cpp
+++ b/js/src/frontend/ParseNode.cpp
@@ -902,3 +902,21 @@ FunctionBox::trace(JSTracer* trc)
     if (enclosingScope_)
         TraceRoot(trc, &enclosingScope_, "funbox-enclosingScope");
 }
+
+bool
+js::frontend::IsAnonymousFunctionDefinition(ParseNode* pn)
+{
+    // ES 2017 draft
+    // 12.15.2 (ArrowFunction, AsyncArrowFunction).
+    // 14.1.12 (FunctionExpression).
+    // 14.4.8 (GeneratorExpression).
+    // 14.6.8 (AsyncFunctionExpression)
+    if (pn->isKind(PNK_FUNCTION) && !pn->pn_funbox->function()->explicitName())
+        return true;
+
+    // 14.5.8 (ClassExpression)
+    if (pn->is<ClassNode>() && !pn->as<ClassNode>().names())
+        return true;
+
+    return false;
+}
diff --git a/js/src/frontend/ParseNode.h b/js/src/frontend/ParseNode.h
index d37aaaae0..ff26279af 100644
--- a/js/src/frontend/ParseNode.h
+++ b/js/src/frontend/ParseNode.h
@@ -450,6 +450,9 @@ class ParseNode
     uint8_t pn_op;      /* see JSOp enum and jsopcode.tbl */
     uint8_t pn_arity:4; /* see ParseNodeArity enum */
     bool pn_parens:1;   /* this expr was enclosed in parens */
+    bool pn_rhs_anon_fun:1;  /* this expr is anonymous function or class that
+                              * is a direct RHS of PNK_ASSIGN or PNK_COLON of
+                              * property, that needs SetFunctionName. */
 
     ParseNode(const ParseNode& other) = delete;
     void operator=(const ParseNode& other) = delete;
@@ -460,6 +463,7 @@ class ParseNode
         pn_op(op),
         pn_arity(arity),
         pn_parens(false),
+        pn_rhs_anon_fun(false),
         pn_pos(0, 0),
         pn_next(nullptr)
     {
@@ -472,6 +476,7 @@ class ParseNode
         pn_op(op),
         pn_arity(arity),
         pn_parens(false),
+        pn_rhs_anon_fun(false),
         pn_pos(pos),
         pn_next(nullptr)
     {
@@ -512,6 +517,13 @@ class ParseNode
     bool isLikelyIIFE() const              { return isInParens(); }
     void setInParens(bool enabled)         { pn_parens = enabled; }
 
+    bool isDirectRHSAnonFunction() const {
+        return pn_rhs_anon_fun;
+    }
+    void setDirectRHSAnonFunction(bool enabled) {
+        pn_rhs_anon_fun = enabled;
+    }
+
     TokenPos            pn_pos;         /* two 16-bit pairs here, for 64 bits */
     ParseNode*          pn_next;        /* intrinsic link in parent PN_LIST */
 
@@ -1444,6 +1456,9 @@ FunctionFormalParametersList(ParseNode* fn, unsigned* numFormals)
     return argsBody->pn_head;
 }
 
+bool
+IsAnonymousFunctionDefinition(ParseNode* pn);
+
 } /* namespace frontend */
 } /* namespace js */
 
diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index f42546eb5..f4c02720a 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -326,10 +326,14 @@ ParseContext::init()
         if (fun->isNamedLambda()) {
             if (!namedLambdaScope_->init(this))
                 return false;
-            AddDeclaredNamePtr p = namedLambdaScope_->lookupDeclaredNameForAdd(fun->name());
+            AddDeclaredNamePtr p =
+                namedLambdaScope_->lookupDeclaredNameForAdd(fun->explicitName());
             MOZ_ASSERT(!p);
-            if (!namedLambdaScope_->addDeclaredName(this, p, fun->name(), DeclarationKind::Const))
+            if (!namedLambdaScope_->addDeclaredName(this, p, fun->explicitName(),
+                                                    DeclarationKind::Const))
+            {
                 return false;
+            }
         }
 
         if (!functionScope_->init(this))
@@ -367,7 +371,7 @@ ParseContext::removeInnerFunctionBoxesForAnnexB(JSAtom* name)
 {
     for (uint32_t i = 0; i < innerFunctionBoxesForAnnexB_->length(); i++) {
         if (FunctionBox* funbox = innerFunctionBoxesForAnnexB_[i]) {
-            if (funbox->function()->name() == name)
+            if (funbox->function()->explicitName() == name)
                 innerFunctionBoxesForAnnexB_[i] = nullptr;
         }
     }
@@ -465,6 +469,7 @@ FunctionBox::FunctionBox(ExclusiveContext* cx, LifoAlloc& alloc, ObjectBox* trac
     usesApply(false),
     usesThis(false),
     usesReturn(false),
+    hasRest_(false),
     funCxFlags()
 {
     // Functions created at parse time may be set singleton after parsing and
@@ -477,7 +482,6 @@ void
 FunctionBox::initFromLazyFunction()
 {
     JSFunction* fun = function();
-    length = fun->nargs() - fun->hasRest();
     if (fun->lazyScript()->isDerivedClassConstructor())
         setDerivedClassConstructor();
     if (fun->lazyScript()->needsHomeObject())
@@ -492,8 +496,6 @@ FunctionBox::initStandaloneFunction(Scope* enclosingScope)
     // Standalone functions are Function or Generator constructors and are
     // always scoped to the global.
     MOZ_ASSERT(enclosingScope->is<GlobalScope>());
-    JSFunction* fun = function();
-    length = fun->nargs() - fun->hasRest();
     enclosingScope_ = enclosingScope;
     allowNewTarget_ = true;
     thisBinding_ = ThisBinding::Function;
@@ -836,7 +838,7 @@ Parser<ParseHandler>::reportBadReturn(Node pn, ParseReportKind kind,
                                       unsigned errnum, unsigned anonerrnum)
 {
     JSAutoByteString name;
-    if (JSAtom* atom = pc->functionBox()->function()->name()) {
+    if (JSAtom* atom = pc->functionBox()->function()->explicitName()) {
         if (!AtomToPrintableString(context, atom, &name))
             return false;
     } else {
@@ -2214,6 +2216,8 @@ Parser<SyntaxParseHandler>::finishFunction()
         lazy->setStrict();
     lazy->setGeneratorKind(funbox->generatorKind());
     lazy->setAsyncKind(funbox->asyncKind());
+    if (funbox->hasRest())
+        lazy->setHasRest();
     if (funbox->isLikelyConstructorWrapper())
         lazy->setLikelyConstructorWrapper();
     if (funbox->isDerivedClassConstructor())
@@ -2757,7 +2761,7 @@ Parser<ParseHandler>::functionArguments(YieldHandling yieldHandling, FunctionSyn
                 }
 
                 hasRest = true;
-                funbox->function()->setHasRest();
+                funbox->setHasRest();
 
                 if (!tokenStream.getToken(&tt))
                     return false;
@@ -3477,8 +3481,8 @@ Parser<ParseHandler>::functionFormalParametersAndBody(InHandling inHandling,
     if (!body)
         return false;
 
-    if ((kind != Method && !IsConstructorKind(kind)) && fun->name()) {
-        RootedPropertyName propertyName(context, fun->name()->asPropertyName());
+    if ((kind != Method && !IsConstructorKind(kind)) && fun->explicitName()) {
+        RootedPropertyName propertyName(context, fun->explicitName()->asPropertyName());
         if (!checkStrictBinding(propertyName, handler.getPosition(pn)))
             return false;
     }
@@ -4337,6 +4341,8 @@ Parser<ParseHandler>::declarationPattern(Node decl, DeclarationKind declKind, To
     if (!init)
         return null();
 
+    handler.checkAndSetIsDirectRHSAnonFunction(init);
+
     if (forHeadKind) {
         // For for(;;) declarations, consistency with |for (;| parsing requires
         // that the ';' first be examined as Operand, even though absence of a
@@ -4366,6 +4372,8 @@ Parser<ParseHandler>::initializerInNameDeclaration(Node decl, Node binding,
     if (!initializer)
         return false;
 
+    handler.checkAndSetIsDirectRHSAnonFunction(initializer);
+
     if (forHeadKind) {
         if (initialDeclaration) {
             bool isForIn, isForOf;
@@ -5063,7 +5071,7 @@ Parser<FullParseHandler>::exportDeclaration()
         if (!kid)
             return null();
 
-        if (!checkExportedName(kid->pn_funbox->function()->name()))
+        if (!checkExportedName(kid->pn_funbox->function()->explicitName()))
             return null();
         break;
 
@@ -6670,8 +6678,6 @@ Parser<ParseHandler>::classDefinition(YieldHandling yieldHandling,
             return null();
         }
 
-        // FIXME: Implement ES6 function "name" property semantics
-        // (bug 883377).
         RootedAtom funName(context);
         switch (propType) {
           case PropertyType::GetterNoExpressionClosure:
@@ -6694,6 +6700,8 @@ Parser<ParseHandler>::classDefinition(YieldHandling yieldHandling,
         if (!fn)
             return null();
 
+        handler.checkAndSetIsDirectRHSAnonFunction(fn);
+
         JSOp op = JSOpFromPropertyType(propType);
         if (!handler.addClassMethodDefinition(classMethods, propName, fn, op, isStatic))
             return null();
@@ -7753,6 +7761,9 @@ Parser<ParseHandler>::assignExpr(InHandling inHandling, YieldHandling yieldHandl
             return null();
     }
 
+    if (kind == PNK_ASSIGN)
+        handler.checkAndSetIsDirectRHSAnonFunction(rhs);
+
     return handler.newAssignment(kind, lhs, rhs, op);
 }
 
@@ -9155,6 +9166,8 @@ Parser<ParseHandler>::objectLiteral(YieldHandling yieldHandling, PossibleError*
             if (!propExpr)
                 return null();
 
+            handler.checkAndSetIsDirectRHSAnonFunction(propExpr);
+
             if (foldConstants && !FoldConstants(context, &propExpr, this))
                 return null();
 
@@ -9268,6 +9281,8 @@ Parser<ParseHandler>::objectLiteral(YieldHandling yieldHandling, PossibleError*
                     return null();
             }
 
+            handler.checkAndSetIsDirectRHSAnonFunction(rhs);
+
             Node propExpr = handler.newAssignment(PNK_ASSIGN, lhs, rhs, JSOP_NOP);
             if (!propExpr)
                 return null();
@@ -9278,8 +9293,6 @@ Parser<ParseHandler>::objectLiteral(YieldHandling yieldHandling, PossibleError*
             if (!abortIfSyntaxParser())
                 return null();
         } else {
-            // FIXME: Implement ES6 function "name" property semantics
-            // (bug 883377).
             RootedAtom funName(context);
             if (!tokenStream.isCurrentTokenType(TOK_RB)) {
                 funName = propAtom;
@@ -9295,6 +9308,8 @@ Parser<ParseHandler>::objectLiteral(YieldHandling yieldHandling, PossibleError*
             if (!fn)
                 return null();
 
+            handler.checkAndSetIsDirectRHSAnonFunction(fn);
+
             JSOp op = JSOpFromPropertyType(propType);
             if (!handler.addObjectMethodDefinition(literal, propName, fn, op))
                 return null();
diff --git a/js/src/frontend/SharedContext.h b/js/src/frontend/SharedContext.h
index 39df47c20..a6ac542f6 100644
--- a/js/src/frontend/SharedContext.h
+++ b/js/src/frontend/SharedContext.h
@@ -471,6 +471,7 @@ class FunctionBox : public ObjectBox, public SharedContext
     bool            usesApply:1;            /* contains an f.apply() call */
     bool            usesThis:1;             /* contains 'this' */
     bool            usesReturn:1;           /* contains a 'return' statement */
+    bool            hasRest_:1;             /* has rest parameter */
 
     FunctionContextFlags funCxFlags;
 
@@ -539,6 +540,11 @@ class FunctionBox : public ObjectBox, public SharedContext
     bool isAsync() const { return asyncKind() == AsyncFunction; }
     bool isArrow() const { return function()->isArrow(); }
 
+    bool hasRest() const { return hasRest_; }
+    void setHasRest() {
+        hasRest_ = true;
+    }
+
     void setGeneratorKind(GeneratorKind kind) {
         // A generator kind can be set at initialization, or when "yield" is
         // first seen.  In both cases the transition can only happen from
@@ -567,7 +573,7 @@ class FunctionBox : public ObjectBox, public SharedContext
     void setHasInnerFunctions()            { funCxFlags.hasInnerFunctions         = true; }
 
     bool hasSimpleParameterList() const {
-        return !function()->hasRest() && !hasParameterExprs && !hasDestructuringArgs;
+        return !hasRest() && !hasParameterExprs && !hasDestructuringArgs;
     }
 
     bool hasMappedArgsObj() const {
diff --git a/js/src/frontend/SyntaxParseHandler.h b/js/src/frontend/SyntaxParseHandler.h
index 75c7e3333..b7f00605b 100644
--- a/js/src/frontend/SyntaxParseHandler.h
+++ b/js/src/frontend/SyntaxParseHandler.h
@@ -339,6 +339,9 @@ class SyntaxParseHandler
                                     Node catchGuard, Node catchBody) { return true; }
 
     MOZ_MUST_USE bool setLastFunctionFormalParameterDefault(Node funcpn, Node pn) { return true; }
+
+    void checkAndSetIsDirectRHSAnonFunction(Node pn) {}
+
     Node newFunctionDefinition() { return NodeFunctionDefinition; }
     bool setComprehensionLambdaBody(Node pn, Node body) { return true; }
     void setFunctionFormalParametersAndBody(Node pn, Node kid) {}
diff --git a/js/src/jit-test/tests/basic/constructor-name.js b/js/src/jit-test/tests/basic/constructor-name.js
index 4bc6a61ea..2dd4c073f 100644
--- a/js/src/jit-test/tests/basic/constructor-name.js
+++ b/js/src/jit-test/tests/basic/constructor-name.js
@@ -17,7 +17,7 @@ function makeObject() {
 let tests = [
   { name: "Ctor",                     object: new Ctor        },
   { name: "nested.Ctor",              object: new nested.Ctor },
-  { name: "makeInstance/LexicalCtor", object: makeInstance()  },
+  { name: "LexicalCtor",              object: makeInstance()  },
   { name: null,                       object: {}              },
   { name: null,                       object: nested.object   },
   { name: null,                       object: makeObject()    },
diff --git a/js/src/jit-test/tests/basic/functionnames.js b/js/src/jit-test/tests/basic/functionnames.js
index 935292ee3..7fef872fc 100644
--- a/js/src/jit-test/tests/basic/functionnames.js
+++ b/js/src/jit-test/tests/basic/functionnames.js
@@ -40,7 +40,7 @@ assertName(Foo, 'Foo</<');
 
 /* various properties and such */
 var x = {fox: { bax: function(){} } };
-assertName(x.fox.bax, 'x.fox.bax');
+assertName(x.fox.bax, 'bax');
 var foo = {foo: {foo: {}}};
 foo.foo.foo = function(){};
 assertName(foo.foo.foo, 'foo.foo.foo');
@@ -48,20 +48,20 @@ var z = {
     foz: function() {
              var baz = function() {
                  var y = {bay: function() {}};
-                 assertName(y.bay, 'z.foz/baz/y.bay');
+                 assertName(y.bay, 'bay');
              };
-             assertName(baz, 'z.foz/baz');
+             assertName(baz, 'baz');
              baz();
          }
 };
-assertName(z.foz, 'z.foz');
+assertName(z.foz, 'foz');
 z.foz();
 
 var outer = function() {
     x.fox.bax.nx = function(){};
     var w = {fow: { baw: function(){} } };
     assertName(x.fox.bax.nx, 'outer/x.fox.bax.nx')
-    assertName(w.fow.baw, 'outer/w.fow.baw');
+    assertName(w.fow.baw, 'baw');
 };
 assertName(outer, 'outer');
 outer();
@@ -69,7 +69,7 @@ function Fuz(){};
 Fuz.prototype = {
   add: function() {}
 }
-assertName(Fuz.prototype.add, 'Fuz.prototype.add');
+assertName(Fuz.prototype.add, 'add');
 
 var x = 1;
 x = function(){};
@@ -94,7 +94,7 @@ a.b = function() {
     assertName(arguments.callee, 'a.b<');
     return { a: function() {} }
 }();
-assertName(a.b.a, 'a.b</<.a');
+assertName(a.b.a, 'a');
 
 a = {
     b: function(a) {
@@ -104,9 +104,9 @@ a = {
             return function() {};
     }
 };
-assertName(a.b, 'a.b');
-assertName(a.b(true), 'a.b/<')
-assertName(a.b(false), 'a.b/<')
+assertName(a.b, 'b');
+assertName(a.b(true), 'b/<')
+assertName(a.b(false), 'b/<')
 
 function f(g) {
     assertName(g, 'x<');
@@ -116,7 +116,7 @@ var x = f(function () { return function() {}; });
 assertName(x, 'x</<');
 
 var a = {'b': function(){}};
-assertName(a.b, 'a.b');
+assertName(a.b, 'b');
 
 function g(f) {
   assertName(f, '');
@@ -138,15 +138,15 @@ a = {
   "\"\'quotes\'\"": function(){},
   "!@#$%": function(){}
 };
-assertName(a["embedded spaces"], 'a["embedded spaces"]');
-assertName(a["dots.look.like.property.references"], 'a["dots.look.like.property.references"]');
-assertName(a["\"\'quotes\'\""], 'a["\\\"\'quotes\'\\\""]');
-assertName(a["!@#$%"], 'a["!@#$%"]');
+assertName(a["embedded spaces"], 'embedded spaces');
+assertName(a["dots.look.like.property.references"], 'dots.look.like.property.references');
+assertName(a["\"\'quotes\'\""], '"\'quotes\'"');
+assertName(a["!@#$%"], '!@#$%');
 
 a.b = {};
 a.b.c = {};
 a.b["c"]["d e"] = { f: { 1: { "g": { "h i": function() {} } } } };
-assertName(a.b.c["d e"].f[1].g["h i"], 'a.b.c["d e"].f[1].g["h i"]');
+assertName(a.b.c["d e"].f[1].g["h i"], 'h i');
 
 this.m = function () {};
 assertName(m, "this.m");
diff --git a/js/src/jit-test/tests/debug/Memory-drainAllocationsLog-16.js b/js/src/jit-test/tests/debug/Memory-drainAllocationsLog-16.js
index b147d6ded..5c73a1ad3 100644
--- a/js/src/jit-test/tests/debug/Memory-drainAllocationsLog-16.js
+++ b/js/src/jit-test/tests/debug/Memory-drainAllocationsLog-16.js
@@ -24,7 +24,7 @@ root.eval(
   this.tests = [
     { name: "Ctor",                     fn: () => new Ctor             },
     { name: "nested.Ctor",              fn: () => new nested.Ctor      },
-    { name: "makeInstance/LexicalCtor", fn: () => makeInstance()       },
+    { name: "LexicalCtor",              fn: () => makeInstance()       },
     { name: null,                       fn: () => ({})                 },
     { name: null,                       fn: () => (nested.object = {}) },
     { name: null,                       fn: () => makeObject()         },
diff --git a/js/src/jit-test/tests/saved-stacks/function-display-name.js b/js/src/jit-test/tests/saved-stacks/function-display-name.js
index cfe175758..f10b7de6b 100644
--- a/js/src/jit-test/tests/saved-stacks/function-display-name.js
+++ b/js/src/jit-test/tests/saved-stacks/function-display-name.js
@@ -2,9 +2,8 @@
 
 function uno() { return dos(); }
 const dos = () => tres.quattro();
-const tres = {
-  quattro: () => saveStack()
-};
+let tres = {};
+tres.quattro = () => saveStack()
 
 const frame = uno();
 
diff --git a/js/src/jit-test/tests/self-test/assertDeepEq.js b/js/src/jit-test/tests/self-test/assertDeepEq.js
index b2a949abc..9c1b37e8e 100644
--- a/js/src/jit-test/tests/self-test/assertDeepEq.js
+++ b/js/src/jit-test/tests/self-test/assertDeepEq.js
@@ -77,7 +77,8 @@ assertDeepEq(q, p);
 assertNotDeepEq(() => 1, () => 2);
 assertNotDeepEq((...x) => 1, x => 1);
 assertNotDeepEq(function f(){}, function g(){});
-var f1 = function () {}, f2 = function () {};
+// Avoid setting name property.
+var [f1, f2] = [function () {}, function () {}];
 assertDeepEq(f1, f1);
 assertDeepEq(f1, f2);  // same text, close enough
 f1.prop = 1;
diff --git a/js/src/jit/BaselineCompiler.cpp b/js/src/jit/BaselineCompiler.cpp
index c58367aa3..4dcc10b61 100644
--- a/js/src/jit/BaselineCompiler.cpp
+++ b/js/src/jit/BaselineCompiler.cpp
@@ -9,6 +9,8 @@
 #include "mozilla/Casting.h"
 #include "mozilla/SizePrintfMacros.h"
 
+#include "jsfun.h"
+
 #include "jit/BaselineIC.h"
 #include "jit/BaselineJIT.h"
 #include "jit/FixedList.h"
@@ -1681,6 +1683,29 @@ BaselineCompiler::emit_JSOP_LAMBDA_ARROW()
     return true;
 }
 
+typedef bool (*SetFunNameFn)(JSContext*, HandleFunction, HandleValue, FunctionPrefixKind);
+static const VMFunction SetFunNameInfo =
+    FunctionInfo<SetFunNameFn>(js::SetFunctionNameIfNoOwnName, "SetFunName");
+
+bool
+BaselineCompiler::emit_JSOP_SETFUNNAME()
+{
+    frame.popRegsAndSync(2);
+
+    frame.push(R0);
+    frame.syncStack(0);
+
+    FunctionPrefixKind prefixKind = FunctionPrefixKind(GET_UINT8(pc));
+    masm.unboxObject(R0, R0.scratchReg());
+
+    prepareVMCall();
+
+    pushArg(Imm32(int32_t(prefixKind)));
+    pushArg(R1);
+    pushArg(R0.scratchReg());
+    return callVM(SetFunNameInfo);
+}
+
 void
 BaselineCompiler::storeValue(const StackValue* source, const Address& dest,
                              const ValueOperand& scratch)
diff --git a/js/src/jit/BaselineCompiler.h b/js/src/jit/BaselineCompiler.h
index 9adf65c27..77f4dd005 100644
--- a/js/src/jit/BaselineCompiler.h
+++ b/js/src/jit/BaselineCompiler.h
@@ -71,6 +71,7 @@ namespace jit {
     _(JSOP_REGEXP)             \
     _(JSOP_LAMBDA)             \
     _(JSOP_LAMBDA_ARROW)       \
+    _(JSOP_SETFUNNAME)         \
     _(JSOP_BITOR)              \
     _(JSOP_BITXOR)             \
     _(JSOP_BITAND)             \
diff --git a/js/src/jit/CodeGenerator.cpp b/js/src/jit/CodeGenerator.cpp
index ce97363be..3b5ec6baa 100644
--- a/js/src/jit/CodeGenerator.cpp
+++ b/js/src/jit/CodeGenerator.cpp
@@ -2548,6 +2548,20 @@ CodeGenerator::emitLambdaInit(Register output, Register envChain,
     masm.storePtr(ImmGCPtr(info.fun->displayAtom()), Address(output, JSFunction::offsetOfAtom()));
 }
 
+typedef bool (*SetFunNameFn)(JSContext*, HandleFunction, HandleValue, FunctionPrefixKind);
+static const VMFunction SetFunNameInfo =
+    FunctionInfo<SetFunNameFn>(js::SetFunctionNameIfNoOwnName, "SetFunName");
+
+void
+CodeGenerator::visitSetFunName(LSetFunName* lir)
+{
+    pushArg(Imm32(lir->mir()->prefixKind()));
+    pushArg(ToValue(lir, LSetFunName::NameValue));
+    pushArg(ToRegister(lir->fun()));
+
+    callVM(SetFunNameInfo, lir);
+}
+
 void
 CodeGenerator::visitOsiPoint(LOsiPoint* lir)
 {
diff --git a/js/src/jit/CodeGenerator.h b/js/src/jit/CodeGenerator.h
index 8f4bcc813..b69e919a3 100644
--- a/js/src/jit/CodeGenerator.h
+++ b/js/src/jit/CodeGenerator.h
@@ -134,6 +134,7 @@ class CodeGenerator final : public CodeGeneratorSpecific
     void visitOutOfLineLambdaArrow(OutOfLineLambdaArrow* ool);
     void visitLambdaArrow(LLambdaArrow* lir);
     void visitLambdaForSingleton(LLambdaForSingleton* lir);
+    void visitSetFunName(LSetFunName* lir);
     void visitPointer(LPointer* lir);
     void visitKeepAliveObject(LKeepAliveObject* lir);
     void visitSlots(LSlots* lir);
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index 1488d7d34..2e7784ff4 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -2122,6 +2122,9 @@ IonBuilder::inspectOpcode(JSOp op)
       case JSOP_LAMBDA_ARROW:
         return jsop_lambda_arrow(info().getFunction(pc));
 
+      case JSOP_SETFUNNAME:
+        return jsop_setfunname(GET_UINT8(pc));
+
       case JSOP_ITER:
         return jsop_iter(GET_INT8(pc));
 
@@ -13340,6 +13343,21 @@ IonBuilder::jsop_lambda_arrow(JSFunction* fun)
 }
 
 bool
+IonBuilder::jsop_setfunname(uint8_t prefixKind)
+{
+    MDefinition* name = current->pop();
+    MDefinition* fun = current->pop();
+    MOZ_ASSERT(fun->type() == MIRType::Object);
+
+    MSetFunName* ins = MSetFunName::New(alloc(), fun, name, prefixKind);
+
+    current->add(ins);
+    current->push(fun);
+
+    return resumeAfter(ins);
+}
+
+bool
 IonBuilder::jsop_setarg(uint32_t arg)
 {
     // To handle this case, we should spill the arguments to the space where
diff --git a/js/src/jit/IonBuilder.h b/js/src/jit/IonBuilder.h
index 38647a88f..0d1bdb1e3 100644
--- a/js/src/jit/IonBuilder.h
+++ b/js/src/jit/IonBuilder.h
@@ -766,6 +766,7 @@ class IonBuilder
     MOZ_MUST_USE bool jsop_object(JSObject* obj);
     MOZ_MUST_USE bool jsop_lambda(JSFunction* fun);
     MOZ_MUST_USE bool jsop_lambda_arrow(JSFunction* fun);
+    MOZ_MUST_USE bool jsop_setfunname(uint8_t prefixKind);
     MOZ_MUST_USE bool jsop_functionthis();
     MOZ_MUST_USE bool jsop_globalthis();
     MOZ_MUST_USE bool jsop_typeof();
diff --git a/js/src/jit/Lowering.cpp b/js/src/jit/Lowering.cpp
index 13e50820e..a21a529be 100644
--- a/js/src/jit/Lowering.cpp
+++ b/js/src/jit/Lowering.cpp
@@ -2460,6 +2460,18 @@ LIRGenerator::visitLambdaArrow(MLambdaArrow* ins)
 }
 
 void
+LIRGenerator::visitSetFunName(MSetFunName* ins)
+{
+    MOZ_ASSERT(ins->fun()->type() == MIRType::Object);
+    MOZ_ASSERT(ins->name()->type() == MIRType::Value);
+
+    LSetFunName* lir = new(alloc()) LSetFunName(useRegisterAtStart(ins->fun()),
+                                                useBoxAtStart(ins->name()));
+    add(lir, ins);
+    assignSafepoint(lir, ins);
+}
+
+void
 LIRGenerator::visitKeepAliveObject(MKeepAliveObject* ins)
 {
     MDefinition* obj = ins->object();
diff --git a/js/src/jit/Lowering.h b/js/src/jit/Lowering.h
index 0f66a3c24..4062c0960 100644
--- a/js/src/jit/Lowering.h
+++ b/js/src/jit/Lowering.h
@@ -185,6 +185,7 @@ class LIRGenerator : public LIRGeneratorSpecific
     void visitNullarySharedStub(MNullarySharedStub* ins);
     void visitLambda(MLambda* ins);
     void visitLambdaArrow(MLambdaArrow* ins);
+    void visitSetFunName(MSetFunName* ins);
     void visitKeepAliveObject(MKeepAliveObject* ins);
     void visitSlots(MSlots* ins);
     void visitElements(MElements* ins);
diff --git a/js/src/jit/MIR.h b/js/src/jit/MIR.h
index dcb08c317..3caa7e357 100644
--- a/js/src/jit/MIR.h
+++ b/js/src/jit/MIR.h
@@ -8464,6 +8464,34 @@ class MLambdaArrow
     }
 };
 
+class MSetFunName
+  : public MAryInstruction<2>,
+    public MixPolicy<ObjectPolicy<0>, BoxPolicy<1> >::Data
+{
+    uint8_t prefixKind_;
+
+    explicit MSetFunName(MDefinition* fun, MDefinition* name, uint8_t prefixKind)
+      : prefixKind_(prefixKind)
+    {
+        initOperand(0, fun);
+        initOperand(1, name);
+        setResultType(MIRType::None);
+    }
+
+  public:
+    INSTRUCTION_HEADER(SetFunName)
+    TRIVIAL_NEW_WRAPPERS
+    NAMED_OPERANDS((0, fun), (1, name))
+
+    uint8_t prefixKind() const {
+        return prefixKind_;
+    }
+
+    bool possiblyCalls() const override {
+        return true;
+    }
+};
+
 // Returns obj->slots.
 class MSlots
   : public MUnaryInstruction,
diff --git a/js/src/jit/MOpcodes.h b/js/src/jit/MOpcodes.h
index 74594cb35..1a6911247 100644
--- a/js/src/jit/MOpcodes.h
+++ b/js/src/jit/MOpcodes.h
@@ -161,6 +161,7 @@ namespace jit {
     _(StringReplace)                                                        \
     _(Lambda)                                                               \
     _(LambdaArrow)                                                          \
+    _(SetFunName)                                                           \
     _(KeepAliveObject)                                                      \
     _(Slots)                                                                \
     _(Elements)                                                             \
diff --git a/js/src/jit/shared/LIR-shared.h b/js/src/jit/shared/LIR-shared.h
index a352f5d8a..f8e0ce9cc 100644
--- a/js/src/jit/shared/LIR-shared.h
+++ b/js/src/jit/shared/LIR-shared.h
@@ -4995,6 +4995,25 @@ class LLambdaArrow : public LInstructionHelper<1, 1 + BOX_PIECES, 0>
     }
 };
 
+class LSetFunName : public LCallInstructionHelper<1, 1 + BOX_PIECES, 0>
+{
+  public:
+    LIR_HEADER(SetFunName)
+
+    static const size_t NameValue = 1;
+
+    LSetFunName(const LAllocation& fun, const LBoxAllocation& name) {
+        setOperand(0, fun);
+        setBoxOperand(NameValue, name);
+    }
+    const LAllocation* fun() {
+        return getOperand(0);
+    }
+    const MSetFunName* mir() const {
+        return mir_->toSetFunName();
+    }
+};
+
 class LKeepAliveObject : public LInstructionHelper<0, 1, 0>
 {
   public:
diff --git a/js/src/jit/shared/LOpcodes-shared.h b/js/src/jit/shared/LOpcodes-shared.h
index bb04553a6..e57751437 100644
--- a/js/src/jit/shared/LOpcodes-shared.h
+++ b/js/src/jit/shared/LOpcodes-shared.h
@@ -242,6 +242,7 @@
     _(Lambda)                       \
     _(LambdaArrow)                  \
     _(LambdaForSingleton)           \
+    _(SetFunName)                   \
     _(KeepAliveObject)              \
     _(Slots)                        \
     _(Elements)                     \
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index e6fc1f98b..85a38bba4 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -2095,7 +2095,7 @@ DefinePropertyById(JSContext* cx, HandleObject obj, HandleId id, HandleValue val
         getter != JS_PropertyStub && setter != JS_StrictPropertyStub)
     {
         if (getter && !(attrs & JSPROP_GETTER)) {
-            RootedAtom atom(cx, IdToFunctionName(cx, id, "get"));
+            RootedAtom atom(cx, IdToFunctionName(cx, id, FunctionPrefixKind::Get));
             if (!atom)
                 return false;
             JSFunction* getobj = NewNativeFunction(cx, (Native) getter, 0, atom);
@@ -2111,7 +2111,7 @@ DefinePropertyById(JSContext* cx, HandleObject obj, HandleId id, HandleValue val
         if (setter && !(attrs & JSPROP_SETTER)) {
             // Root just the getter, since the setter is not yet a JSObject.
             AutoRooterGetterSetter getRoot(cx, JSPROP_GETTER, &getter, nullptr);
-            RootedAtom atom(cx, IdToFunctionName(cx, id, "set"));
+            RootedAtom atom(cx, IdToFunctionName(cx, id, FunctionPrefixKind::Set));
             if (!atom)
                 return false;
             JSFunction* setobj = NewNativeFunction(cx, (Native) setter, 1, atom);
@@ -3435,10 +3435,7 @@ JS::NewFunctionFromSpec(JSContext* cx, const JSFunctionSpec* fs, HandleId id)
         {
             return nullptr;
         }
-        JSFunction* fun = &funVal.toObject().as<JSFunction>();
-        if (fs->flags & JSFUN_HAS_REST)
-            fun->setHasRest();
-        return fun;
+        return &funVal.toObject().as<JSFunction>();
     }
 
     RootedAtom atom(cx, IdToFunctionName(cx, id));
@@ -3618,7 +3615,7 @@ JS_GetFunctionObject(JSFunction* fun)
 JS_PUBLIC_API(JSString*)
 JS_GetFunctionId(JSFunction* fun)
 {
-    return fun->name();
+    return fun->explicitName();
 }
 
 JS_PUBLIC_API(JSString*)
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 332ce8562..cbef0f8fb 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -875,11 +875,7 @@ class MOZ_STACK_CLASS SourceBufferHolder final
 
 #define JSFUN_CONSTRUCTOR      0x400    /* native that can be called as a ctor */
 
-//                             0x800    /* Unused */
-
-#define JSFUN_HAS_REST        0x1000    /* function has ...rest parameter. */
-
-#define JSFUN_FLAGS_MASK      0x1e00    /* | of all the JSFUN_* flags */
+#define JSFUN_FLAGS_MASK       0x600    /* | of all the JSFUN_* flags */
 
 /*
  * If set, will allow redefining a non-configurable property, but only on a
diff --git a/js/src/jsatom.cpp b/js/src/jsatom.cpp
index 3f8e8d8f8..2a3c58638 100644
--- a/js/src/jsatom.cpp
+++ b/js/src/jsatom.cpp
@@ -510,6 +510,14 @@ ToAtomSlow(ExclusiveContext* cx, typename MaybeRooted<Value, allowGC>::HandleTyp
         return v.toBoolean() ? cx->names().true_ : cx->names().false_;
     if (v.isNull())
         return cx->names().null;
+    if (v.isSymbol()) {
+        if (cx->shouldBeJSContext() && allowGC) {
+            JS_ReportErrorNumberASCII(cx->asJSContext(), GetErrorMessage, nullptr,
+                                      JSMSG_SYMBOL_TO_STRING);
+        }
+        return nullptr;
+    }
+    MOZ_ASSERT(v.isUndefined());
     return cx->names().undefined;
 }
 
diff --git a/js/src/jscntxt.cpp b/js/src/jscntxt.cpp
index 3ffd9ad7b..31d62332d 100644
--- a/js/src/jscntxt.cpp
+++ b/js/src/jscntxt.cpp
@@ -803,7 +803,7 @@ js::ReportMissingArg(JSContext* cx, HandleValue v, unsigned arg)
 
     SprintfLiteral(argbuf, "%u", arg);
     if (IsFunctionObject(v)) {
-        RootedAtom name(cx, v.toObject().as<JSFunction>().name());
+        RootedAtom name(cx, v.toObject().as<JSFunction>().explicitName());
         bytes = DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, v, name);
         if (!bytes)
             return;
diff --git a/js/src/jsfun.cpp b/js/src/jsfun.cpp
index 1e1b76d5d..bcb0da80b 100644
--- a/js/src/jsfun.cpp
+++ b/js/src/jsfun.cpp
@@ -562,7 +562,7 @@ js::XDRInterpretedFunction(XDRState<mode>* xdr, HandleScope enclosingScope,
             return false;
         }
 
-        if (fun->name() || fun->hasGuessedAtom())
+        if (fun->explicitName() || fun->hasCompileTimeName() || fun->hasGuessedAtom())
             firstword |= HasAtom;
 
         if (fun->isStarGenerator())
@@ -1042,8 +1042,8 @@ js::FunctionToString(JSContext* cx, HandleFunction fun, bool prettyPrint)
         if (!ok)
             return nullptr;
     }
-    if (fun->name()) {
-        if (!out.append(fun->name()))
+    if (fun->explicitName()) {
+        if (!out.append(fun->explicitName()))
             return nullptr;
     }
 
@@ -1329,8 +1329,7 @@ JSFunction::getLength(JSContext* cx, uint16_t* length)
     if (self->isInterpretedLazy() && !self->getOrCreateScript(cx))
         return false;
 
-    *length = self->hasScript() ? self->nonLazyScript()->funLength()
-                                : (self->nargs() - self->hasRest());
+    *length = self->isNative() ? self->nargs() : self->nonLazyScript()->funLength();
     return true;
 }
 
@@ -1365,14 +1364,14 @@ JSFunction::getUnresolvedName(JSContext* cx)
     if (isClassConstructor()) {
         // It's impossible to have an empty named class expression. We use
         // empty as a sentinel when creating default class constructors.
-        MOZ_ASSERT(name() != cx->names().empty);
+        MOZ_ASSERT(explicitOrCompileTimeName() != cx->names().empty);
 
         // Unnamed class expressions should not get a .name property at all.
-        return name();
+        return explicitOrCompileTimeName();
     }
 
-    // Returns the empty string for unnamed functions (FIXME: bug 883377).
-    return name() != nullptr ? name() : cx->names().empty;
+    return explicitOrCompileTimeName() != nullptr ? explicitOrCompileTimeName()
+                                                  : cx->names().empty;
 }
 
 static const js::Value&
@@ -1620,7 +1619,7 @@ const JSFunctionSpec js::function_methods[] = {
     JS_FN(js_apply_str,      fun_apply,      2,0),
     JS_FN(js_call_str,       fun_call,       1,0),
     JS_FN("isGenerator",     fun_isGenerator,0,0),
-    JS_SELF_HOSTED_FN("bind", "FunctionBind", 2, JSFUN_HAS_REST),
+    JS_SELF_HOSTED_FN("bind", "FunctionBind", 2, 0),
     JS_SYM_FN(hasInstance, fun_symbolHasInstance, 1, JSPROP_READONLY | JSPROP_PERMANENT),
     JS_FS_END
 };
@@ -2132,34 +2131,115 @@ js::CloneFunctionAndScript(JSContext* cx, HandleFunction fun, HandleObject enclo
  *
  * Function names are always strings. If id is the well-known @@iterator
  * symbol, this returns "[Symbol.iterator]".  If a prefix is supplied the final
- * name is |prefix + " " + name|.
+ * name is |prefix + " " + name|. A prefix cannot be supplied if id is a
+ * symbol value.
  *
- * Implements step 4 and 5 of SetFunctionName in ES 2016 draft Dec 20, 2015.
+ * Implements steps 3-5 of 9.2.11 SetFunctionName in ES2016.
  */
 JSAtom*
-js::IdToFunctionName(JSContext* cx, HandleId id, const char* prefix /* = nullptr */)
+js::IdToFunctionName(JSContext* cx, HandleId id,
+                     FunctionPrefixKind prefixKind /* = FunctionPrefixKind::None */)
 {
-    if (JSID_IS_ATOM(id) && !prefix)
+    // No prefix fastpath.
+    if (JSID_IS_ATOM(id) && prefixKind == FunctionPrefixKind::None)
         return JSID_TO_ATOM(id);
 
-    if (JSID_IS_SYMBOL(id) && !prefix) {
+    // Step 3 (implicit).
+
+    // Step 4.
+    if (JSID_IS_SYMBOL(id)) {
+        // Step 4.a.
         RootedAtom desc(cx, JSID_TO_SYMBOL(id)->description());
+
+        // Step 4.b, no prefix fastpath.
+        if (!desc && prefixKind == FunctionPrefixKind::None)
+            return cx->names().empty;
+
+        // Step 5 (reordered).
         StringBuffer sb(cx);
-        if (!sb.append('[') || !sb.append(desc) || !sb.append(']'))
-            return nullptr;
+        if (prefixKind == FunctionPrefixKind::Get) {
+            if (!sb.append("get "))
+                return nullptr;
+        } else if (prefixKind == FunctionPrefixKind::Set) {
+            if (!sb.append("set "))
+                return nullptr;
+        }
+
+        // Step 4.b.
+        if (desc) {
+            // Step 4.c.
+            if (!sb.append('[') || !sb.append(desc) || !sb.append(']'))
+                return nullptr;
+        }
         return sb.finishAtom();
     }
 
     RootedValue idv(cx, IdToValue(id));
-    if (!prefix)
-        return ToAtom<CanGC>(cx, idv);
+    RootedAtom name(cx, ToAtom<CanGC>(cx, idv));
+    if (!name)
+        return nullptr;
+
+    // Step 5.
+    return NameToFunctionName(cx, name, prefixKind);
+}
+
+JSAtom*
+js::NameToFunctionName(ExclusiveContext* cx, HandleAtom name,
+                       FunctionPrefixKind prefixKind /* = FunctionPrefixKind::None */)
+{
+    if (prefixKind == FunctionPrefixKind::None)
+        return name;
 
     StringBuffer sb(cx);
-    if (!sb.append(prefix, strlen(prefix)) || !sb.append(' ') || !sb.append(ToAtom<CanGC>(cx, idv)))
+    if (prefixKind == FunctionPrefixKind::Get) {
+        if (!sb.append("get "))
+            return nullptr;
+    } else {
+        if (!sb.append("set "))
+            return nullptr;
+    }
+    if (!sb.append(name))
         return nullptr;
     return sb.finishAtom();
 }
 
+bool
+js::SetFunctionNameIfNoOwnName(JSContext* cx, HandleFunction fun, HandleValue name,
+                               FunctionPrefixKind prefixKind)
+{
+    MOZ_ASSERT(name.isString() || name.isSymbol() || name.isNumber());
+
+    if (fun->isClassConstructor()) {
+        // A class may have static 'name' method or accessor.
+        RootedId nameId(cx, NameToId(cx->names().name));
+        bool result;
+        if (!HasOwnProperty(cx, fun, nameId, &result))
+            return false;
+
+        if (result)
+            return true;
+    } else {
+        // Anonymous function shouldn't have own 'name' property at this point.
+        MOZ_ASSERT(!fun->containsPure(cx->names().name));
+    }
+
+    RootedId id(cx);
+    if (!ValueToId<CanGC>(cx, name, &id))
+        return false;
+
+    RootedAtom funNameAtom(cx, IdToFunctionName(cx, id, prefixKind));
+    if (!funNameAtom)
+        return false;
+
+    RootedValue funNameVal(cx, StringValue(funNameAtom));
+    if (!NativeDefineProperty(cx, fun, cx->names().name, funNameVal, nullptr, nullptr,
+                              JSPROP_READONLY))
+    {
+        return false;
+    }
+    return true;
+}
+
 JSFunction*
 js::DefineFunction(JSContext* cx, HandleObject obj, HandleId id, Native native,
                    unsigned nargs, unsigned flags, AllocKind allocKind /* = AllocKind::FUNCTION */)
diff --git a/js/src/jsfun.h b/js/src/jsfun.h
index 88af5c22d..d45d112a5 100644
--- a/js/src/jsfun.h
+++ b/js/src/jsfun.h
@@ -31,6 +31,12 @@ static const uint32_t JSSLOT_BOUND_FUNCTION_ARGS       = 4;
 static const char FunctionConstructorMedialSigils[] = ") {\n";
 static const char FunctionConstructorFinalBrace[] = "\n}";
 
+enum class FunctionPrefixKind {
+    None,
+    Get,
+    Set
+};
+
 class JSFunction : public js::NativeObject
 {
   public:
@@ -61,7 +67,9 @@ class JSFunction : public js::NativeObject
                                        function-statement) */
         SELF_HOSTED      = 0x0080,  /* function is self-hosted builtin and must not be
                                        decompilable nor constructible. */
-        HAS_REST         = 0x0100,  /* function has a rest (...) parameter */
+        HAS_COMPILE_TIME_NAME = 0x0100, /* function had no explicit name, but a
+                                           name was set by SetFunctionName
+                                           at compile time */
         INTERPRETED_LAZY = 0x0200,  /* function is interpreted but doesn't have a script yet */
         RESOLVED_LENGTH  = 0x0400,  /* f.length has been resolved (see fun_resolve). */
         RESOLVED_NAME    = 0x0800,  /* f.name has been resolved (see fun_resolve). */
@@ -95,7 +103,7 @@ class JSFunction : public js::NativeObject
         NO_XDR_FLAGS = RESOLVED_LENGTH | RESOLVED_NAME,
 
         STABLE_ACROSS_CLONES = CONSTRUCTOR | EXPR_BODY | HAS_GUESSED_ATOM | LAMBDA |
-                               SELF_HOSTED |  HAS_REST | FUNCTION_KIND_MASK
+                               SELF_HOSTED | HAS_COMPILE_TIME_NAME | FUNCTION_KIND_MASK
     };
 
     static_assert((INTERPRETED | INTERPRETED_LAZY) == js::JS_FUNCTION_INTERPRETED_BITS,
@@ -180,10 +188,10 @@ class JSFunction : public js::NativeObject
 
     /* Possible attributes of an interpreted function: */
     bool isExprBody()               const { return flags() & EXPR_BODY; }
+    bool hasCompileTimeName()       const { return flags() & HAS_COMPILE_TIME_NAME; }
     bool hasGuessedAtom()           const { return flags() & HAS_GUESSED_ATOM; }
     bool isLambda()                 const { return flags() & LAMBDA; }
     bool isBoundFunction()          const { return flags() & BOUND_FUN; }
-    bool hasRest()                  const { return flags() & HAS_REST; }
     bool isInterpretedLazy()        const { return flags() & INTERPRETED_LAZY; }
     bool hasScript()                const { return flags() & INTERPRETED; }
 
@@ -222,7 +230,7 @@ class JSFunction : public js::NativeObject
     }
 
     bool isNamedLambda() const {
-        return isLambda() && displayAtom() && !hasGuessedAtom();
+        return isLambda() && displayAtom() && !hasCompileTimeName() && !hasGuessedAtom();
     }
 
     bool hasLexicalThis() const {
@@ -264,11 +272,6 @@ class JSFunction : public js::NativeObject
         this->nargs_ = nargs;
     }
 
-    // Can be called multiple times by the parser.
-    void setHasRest() {
-        flags_ |= HAS_REST;
-    }
-
     void setIsBoundFunction() {
         MOZ_ASSERT(!isBoundFunction());
         flags_ |= BOUND_FUN;
@@ -315,14 +318,12 @@ class JSFunction : public js::NativeObject
 
     JSAtom* getUnresolvedName(JSContext* cx);
 
-    JSAtom* name() const { return hasGuessedAtom() ? nullptr : atom_.get(); }
-
-    // Because display names (see Debugger.Object.displayName) are already stored
-    // on functions and will always contain a valid es6 function name, as described
-    // in "ECMA-262 (2016-02-27) 9.2.11 SetFunctionName," we have opted to save
-    // memory by parsing the existing display name when a function's name property
-    // is accessed.
-    JSAtom* functionName(JSContext* cx) const;
+    JSAtom* explicitName() const {
+        return (hasCompileTimeName() || hasGuessedAtom()) ? nullptr : atom_.get();
+    }
+    JSAtom* explicitOrCompileTimeName() const {
+        return hasGuessedAtom() ? nullptr : atom_.get();
+    }
 
     void initAtom(JSAtom* atom) { atom_.init(atom); }
 
@@ -332,9 +333,24 @@ class JSFunction : public js::NativeObject
         return atom_;
     }
 
+    void setCompileTimeName(JSAtom* atom) {
+        MOZ_ASSERT(!atom_);
+        MOZ_ASSERT(atom);
+        MOZ_ASSERT(!hasGuessedAtom());
+        MOZ_ASSERT(!isClassConstructor());
+        atom_ = atom;
+        flags_ |= HAS_COMPILE_TIME_NAME;
+    }
+    JSAtom* compileTimeName() const {
+        MOZ_ASSERT(hasCompileTimeName());
+        MOZ_ASSERT(atom_);
+        return atom_;
+    }
+
     void setGuessedAtom(JSAtom* atom) {
         MOZ_ASSERT(!atom_);
         MOZ_ASSERT(atom);
+        MOZ_ASSERT(!hasCompileTimeName());
         MOZ_ASSERT(!hasGuessedAtom());
         atom_ = atom;
         flags_ |= HAS_GUESSED_ATOM;
@@ -679,7 +695,16 @@ NewFunctionWithProto(ExclusiveContext* cx, JSNative native, unsigned nargs,
                      NewFunctionProtoHandling protoHandling = NewFunctionClassProto);
 
 extern JSAtom*
-IdToFunctionName(JSContext* cx, HandleId id, const char* prefix = nullptr);
+IdToFunctionName(JSContext* cx, HandleId id,
+                 FunctionPrefixKind prefixKind = FunctionPrefixKind::None);
+
+extern JSAtom*
+NameToFunctionName(ExclusiveContext* cx, HandleAtom name,
+                   FunctionPrefixKind prefixKind = FunctionPrefixKind::None);
+
+extern bool
+SetFunctionNameIfNoOwnName(JSContext* cx, HandleFunction fun, HandleValue name,
+                           FunctionPrefixKind prefixKind);
 
 extern JSFunction*
 DefineFunction(JSContext* cx, HandleObject obj, HandleId id, JSNative native,
diff --git a/js/src/jsfuninlines.h b/js/src/jsfuninlines.h
index 8286a7d6a..e134def61 100644
--- a/js/src/jsfuninlines.h
+++ b/js/src/jsfuninlines.h
@@ -16,7 +16,7 @@ namespace js {
 inline const char*
 GetFunctionNameBytes(JSContext* cx, JSFunction* fun, JSAutoByteString* bytes)
 {
-    if (JSAtom* name = fun->name())
+    if (JSAtom* name = fun->explicitName())
         return bytes->encodeLatin1(cx, name);
     return js_anonymous_str;
 }
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index b568b4b30..929251d8b 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -316,6 +316,7 @@ js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScrip
         IsLegacyGenerator,
         IsStarGenerator,
         IsAsync,
+        HasRest,
         OwnSource,
         ExplicitUseStrict,
         SelfHosted,
@@ -431,6 +432,8 @@ js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScrip
             scriptBits |= (1 << IsStarGenerator);
         if (script->asyncKind() == AsyncFunction)
             scriptBits |= (1 << IsAsync);
+        if (script->hasRest())
+            scriptBits |= (1 << HasRest);
         if (script->hasSingletons())
             scriptBits |= (1 << HasSingleton);
         if (script->treatAsRunOnce())
@@ -582,6 +585,8 @@ js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScrip
 
         if (scriptBits & (1 << IsAsync))
             script->setAsyncKind(AsyncFunction);
+        if (scriptBits & (1 << HasRest))
+            script->setHasRest();
     }
 
     JS_STATIC_ASSERT(sizeof(jsbytecode) == 1);
@@ -2637,6 +2642,8 @@ JSScript::initFromFunctionBox(ExclusiveContext* cx, HandleScript script,
     script->isGeneratorExp_ = funbox->isGenexpLambda;
     script->setGeneratorKind(funbox->generatorKind());
     script->setAsyncKind(funbox->asyncKind());
+    if (funbox->hasRest())
+        script->setHasRest();
 
     PositionalFormalParameterIter fi(script);
     while (fi && !fi.closedOver())
@@ -3295,6 +3302,7 @@ js::detail::CopyScript(JSContext* cx, HandleScript src, HandleScript dst,
     dst->needsHomeObject_ = src->needsHomeObject();
     dst->isDefaultClassConstructor_ = src->isDefaultClassConstructor();
     dst->isAsync_ = src->asyncKind() == AsyncFunction;
+    dst->hasRest_ = src->hasRest_;
 
     if (nconsts != 0) {
         GCPtrValue* vector = Rebase<GCPtrValue>(dst, src, src->consts()->vector);
@@ -4028,6 +4036,7 @@ LazyScript::Create(ExclusiveContext* cx, HandleFunction fun,
     p.shouldDeclareArguments = false;
     p.hasThisBinding = false;
     p.isAsync = false;
+    p.hasRest = false;
     p.numClosedOverBindings = closedOverBindings.length();
     p.numInnerFunctions = innerFunctions.length();
     p.generatorKindBits = GeneratorKindAsBits(NotGenerator);
@@ -4169,7 +4178,7 @@ JSScript::hasLoops()
 bool
 JSScript::mayReadFrameArgsDirectly()
 {
-    return argumentsHasVarBinding() || (function() && function()->hasRest());
+    return argumentsHasVarBinding() || hasRest();
 }
 
 static inline void
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index ffd4b1e2e..690bc225d 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -1012,6 +1012,8 @@ class JSScript : public js::gc::TenuredCell
 
     bool isAsync_:1;
 
+    bool hasRest_:1;
+
     // Add padding so JSScript is gc::Cell aligned. Make padding protected
     // instead of private to suppress -Wunused-private-field compiler warnings.
   protected:
@@ -1308,6 +1310,13 @@ class JSScript : public js::gc::TenuredCell
         isAsync_ = kind == js::AsyncFunction;
     }
 
+    bool hasRest() const {
+        return hasRest_;
+    }
+    void setHasRest() {
+        hasRest_ = true;
+    }
+
     void setNeedsHomeObject() {
         needsHomeObject_ = true;
     }
@@ -1940,6 +1949,7 @@ class LazyScript : public gc::TenuredCell
         uint32_t treatAsRunOnce : 1;
         uint32_t isDerivedClassConstructor : 1;
         uint32_t needsHomeObject : 1;
+        uint32_t hasRest : 1;
     };
 
     union {
@@ -2068,6 +2078,13 @@ class LazyScript : public gc::TenuredCell
         p_.isAsync = kind == AsyncFunction;
     }
 
+    bool hasRest() const {
+        return p_.hasRest;
+    }
+    void setHasRest() {
+        p_.hasRest = true;
+    }
+
     bool strict() const {
         return p_.strict;
     }
diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index 32a85dc13..7adeed620 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -2894,7 +2894,7 @@ static const JSFunctionSpec string_static_methods[] = {
     JS_INLINABLE_FN("fromCharCode", js::str_fromCharCode, 1, 0, StringFromCharCode),
     JS_INLINABLE_FN("fromCodePoint", js::str_fromCodePoint, 1, 0, StringFromCodePoint),
 
-    JS_SELF_HOSTED_FN("raw",             "String_static_raw",           2,JSFUN_HAS_REST),
+    JS_SELF_HOSTED_FN("raw",             "String_static_raw",           2,0),
     JS_SELF_HOSTED_FN("substring",       "String_static_substring",     3,0),
     JS_SELF_HOSTED_FN("substr",          "String_static_substr",        3,0),
     JS_SELF_HOSTED_FN("slice",           "String_static_slice",         3,0),
diff --git a/js/src/tests/ecma_5/extensions/error-tostring-function.js b/js/src/tests/ecma_5/extensions/error-tostring-function.js
index 5e92f1075..86751c39d 100644
--- a/js/src/tests/ecma_5/extensions/error-tostring-function.js
+++ b/js/src/tests/ecma_5/extensions/error-tostring-function.js
@@ -27,7 +27,7 @@ assertEq(ErrorToString(function(){}), "");
 
 var fn1 = function() {};
 fn1.message = "ohai";
-assertEq(ErrorToString(fn1), "ohai");
+assertEq(ErrorToString(fn1), "fn1: ohai");
 
 var fn2 = function blerch() {};
 fn2.message = "fnord";
@@ -35,7 +35,7 @@ assertEq(ErrorToString(fn2), "blerch: fnord");
 
 var fn3 = function() {};
 fn3.message = "";
-assertEq(ErrorToString(fn3), "");
+assertEq(ErrorToString(fn3), "fn3");
 
 /******************************************************************************/
 
diff --git a/js/src/tests/ecma_6/Class/className.js b/js/src/tests/ecma_6/Class/className.js
index a33397a8a..ad3920c15 100644
--- a/js/src/tests/ecma_6/Class/className.js
+++ b/js/src/tests/ecma_6/Class/className.js
@@ -174,27 +174,29 @@ testName(ExtendedExpr3, "base", false, false, false);
 
 // Anonymous class expressions don't get name properties unless specified in a
 // static manner.
-let Anon = class {
+// Use property assignment to avoid setting name property.
+let tmp = {};
+let Anon = tmp.value = class {
     constructor() {}
 };
 testName(Anon, "", false, false, false);
 
-let AnonDefault = class { };
+let AnonDefault = tmp.value = class { };
 testName(AnonDefault, "", false, false, false);
 
-let AnonWithGetter = class {
+let AnonWithGetter = tmp.value = class {
     constructor() {}
     static get name() { return "base"; }
 };
 testName(AnonWithGetter, "base", false, true, false);
 
-let AnonWithSetter = class {
+let AnonWithSetter = tmp.value = class {
     constructor() {}
     static set name(v) {}
 };
 testName(AnonWithSetter, undefined, false, false, true);
 
-let AnonWithGetterSetter = class {
+let AnonWithGetterSetter = tmp.value = class {
     constructor() {}
     static get name() { return "base"; }
     static set name(v) {}
@@ -202,15 +204,15 @@ let AnonWithGetterSetter = class {
 testName(AnonWithGetterSetter, "base", false, true, true);
 
 
-let ExtendedAnon1 = class extends Anon {
+let ExtendedAnon1 = tmp.value = class extends Anon {
     constructor() {}
 };
 testName(ExtendedAnon1, "", false, false, false);
 
-let ExtendedAnonDefault = class extends Anon { };
+let ExtendedAnonDefault = tmp.value = class extends Anon { };
 testName(ExtendedAnonDefault, "", false, false, false);
 
-let ExtendedAnon2 = class extends AnonWithGetterSetter {
+let ExtendedAnon2 = tmp.value = class extends AnonWithGetterSetter {
     constructor() {}
     static get name() { return "extend"; }
 };
@@ -218,7 +220,7 @@ testName(ExtendedAnon2, "extend", false, true, false);
 delete ExtendedAnon2.name;
 testName(ExtendedAnon2, "base", false, false, false);
 
-let ExtendedAnon3 = class extends AnonWithGetterSetter {
+let ExtendedAnon3 = tmp.value = class extends AnonWithGetterSetter {
     constructor() {}
     static set name(v) {}
 };
diff --git a/js/src/tests/ecma_6/Function/function-name-assignment.js b/js/src/tests/ecma_6/Function/function-name-assignment.js
new file mode 100644
index 000000000..5e4d1c004
--- /dev/null
+++ b/js/src/tests/ecma_6/Function/function-name-assignment.js
@@ -0,0 +1,139 @@
+var BUGNUMBER = 883377;
+var summary = "Anonymous function name should be set based on assignment";
+
+print(BUGNUMBER + ": " + summary);
+
+var fooSymbol = Symbol("foo");
+var emptySymbol = Symbol("");
+var undefSymbol = Symbol();
+var globalVar;
+
+var exprs = [
+    ["function() {}", false],
+    ["function named() {}", true],
+    ["function*() {}", false],
+    ["function* named() {}", true],
+    ["async function() {}", false],
+    ["async function named() {}", true],
+    ["() => {}", false],
+    ["async () => {}", false],
+    ["class {}", false],
+    ["class named {}", true],
+];
+
+function testAssignmentExpression(expr, named) {
+    eval(`
+    var assignment;
+    assignment = ${expr};
+    assertEq(assignment.name, named ? "named" : "assignment");
+
+    globalVar = ${expr};
+    assertEq(globalVar.name, named ? "named" : "globalVar");
+
+    var obj = { dynamic: null };
+    with (obj) {
+        dynamic = ${expr};
+    }
+    assertEq(obj.dynamic.name, named ? "named" : "dynamic");
+
+    (function namedLambda(param1, param2) {
+        var assignedToNamedLambda;
+        assignedToNamedLambda = namedLambda = ${expr};
+        assertEq(namedLambda.name, "namedLambda");
+        assertEq(assignedToNamedLambda.name, named ? "named" : "namedLambda");
+
+        param1 = ${expr};
+        assertEq(param1.name, named ? "named" : "param1");
+
+        {
+            let param1 = ${expr};
+            assertEq(param1.name, named ? "named" : "param1");
+
+            param2 = ${expr};
+            assertEq(param2.name, named ? "named" : "param2");
+        }
+    })();
+
+    {
+        let nextedLexical1, nextedLexical2;
+        {
+            let nextedLexical1 = ${expr};
+            assertEq(nextedLexical1.name, named ? "named" : "nextedLexical1");
+
+            nextedLexical2 = ${expr};
+            assertEq(nextedLexical2.name, named ? "named" : "nextedLexical2");
+        }
+    }
+    `);
+
+    // Not applicable cases: not IsIdentifierRef.
+    eval(`
+    var inParen;
+    (inParen) = ${expr};
+    assertEq(inParen.name, named ? "named" : "");
+    `);
+
+    // Not applicable cases: not direct RHS.
+    if (!expr.includes("=>")) {
+        eval(`
+        var a = true && ${expr};
+        assertEq(a.name, named ? "named" : "");
+        `);
+    } else {
+        // Arrow function cannot be RHS of &&.
+        eval(`
+        var a = true && (${expr});
+        assertEq(a.name, named ? "named" : "");
+        `);
+    }
+
+    // Not applicable cases: property.
+    eval(`
+    var obj = {};
+
+    obj.prop = ${expr};
+    assertEq(obj.prop.name, named ? "named" : "");
+
+    obj["literal"] = ${expr};
+    assertEq(obj["literal"].name, named ? "named" : "");
+    `);
+
+    // Not applicable cases: assigned again.
+    eval(`
+    var tmp = [${expr}];
+    assertEq(tmp[0].name, named ? "named" : "");
+
+    var assignment;
+    assignment = tmp[0];
+    assertEq(assignment.name, named ? "named" : "");
+    `);
+}
+for (var [expr, named] of exprs) {
+    testAssignmentExpression(expr, named);
+}
+
+function testVariableDeclaration(expr, named) {
+    eval(`
+    var varDecl = ${expr};
+    assertEq(varDecl.name, named ? "named" : "varDecl");
+    `);
+}
+for (var [expr, named] of exprs) {
+    testVariableDeclaration(expr, named);
+}
+
+function testLexicalBinding(expr, named) {
+    eval(`
+    let lexical = ${expr};
+    assertEq(lexical.name, named ? "named" : "lexical");
+
+    const constLexical = ${expr};
+    assertEq(constLexical.name, named ? "named" : "constLexical");
+    `);
+}
+for (var [expr, named] of exprs) {
+    testLexicalBinding(expr, named);
+}
+
+if (typeof reportCompare === "function")
+    reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/Function/function-name-binding.js b/js/src/tests/ecma_6/Function/function-name-binding.js
new file mode 100644
index 000000000..bdd6c131c
--- /dev/null
+++ b/js/src/tests/ecma_6/Function/function-name-binding.js
@@ -0,0 +1,54 @@
+var BUGNUMBER = 883377;
+var summary = "Anonymous function name should be set based on binding pattern";
+
+print(BUGNUMBER + ": " + summary);
+
+var exprs = [
+    ["function() {}", false],
+    ["function named() {}", true],
+    ["function*() {}", false],
+    ["function* named() {}", true],
+    ["async function() {}", false],
+    ["async function named() {}", true],
+    ["() => {}", false],
+    ["async () => {}", false],
+    ["class {}", false],
+    ["class named {}", true],
+];
+
+function testAssignmentProperty(expr, named) {
+    var f = eval(`(function({ prop1 = ${expr} }) { return prop1; })`);
+    assertEq(f({}).name, named ? "named" : "prop1");
+
+    eval(`
+    var { prop1 = ${expr} } = {};
+    assertEq(prop1.name, named ? "named" : "prop1");
+    `);
+}
+for (var [expr, named] of exprs) {
+    testAssignmentProperty(expr, named);
+}
+
+function testAssignmentElement(expr, named) {
+    var f = eval(`(function([elem1 = ${expr}]) { return elem1; })`);
+    assertEq(f([]).name, named ? "named" : "elem1");
+
+    eval(`
+    var [elem1 = ${expr}] = [];
+    assertEq(elem1.name, named ? "named" : "elem1");
+    `);
+}
+for (var [expr, named] of exprs) {
+    testAssignmentElement(expr, named);
+}
+
+function testSingleNameBinding(expr, named) {
+    var f = eval(`(function(param1 = ${expr}) { return param1; })`);
+    assertEq(f().name, named ? "named" : "param1");
+}
+for (var [expr, named] of exprs) {
+    testSingleNameBinding(expr, named);
+}
+
+if (typeof reportCompare === "function")
+    reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/Function/function-name-class.js b/js/src/tests/ecma_6/Function/function-name-class.js
new file mode 100644
index 000000000..edde69055
--- /dev/null
+++ b/js/src/tests/ecma_6/Function/function-name-class.js
@@ -0,0 +1,32 @@
+var BUGNUMBER = 883377;
+var summary = "Anonymous class with name method shouldn't be affected by assignment";
+
+print(BUGNUMBER + ": " + summary);
+
+var classWithStaticNameMethod = class { static name() {} };
+assertEq(typeof classWithStaticNameMethod.name, "function");
+
+var classWithStaticNameGetter = class { static get name() { return "static name"; } };
+assertEq(typeof Object.getOwnPropertyDescriptor(classWithStaticNameGetter, "name").get, "function");
+assertEq(classWithStaticNameGetter.name, "static name");
+
+var classWithStaticNameSetter = class { static set name(v) {} };
+assertEq(typeof Object.getOwnPropertyDescriptor(classWithStaticNameSetter, "name").set, "function");
+
+var n = "NAME".toLowerCase();
+var classWithStaticNameMethodComputed = class { static [n]() {} };
+assertEq(typeof classWithStaticNameMethodComputed.name, "function");
+
+// It doesn't apply for non-static method.
+
+var classWithNameMethod = class { name() {} };
+assertEq(classWithNameMethod.name, "classWithNameMethod");
+
+var classWithNameGetter = class { get name() { return "name"; } };
+assertEq(classWithNameGetter.name, "classWithNameGetter");
+
+var classWithNameSetter = class { set name(v) {} };
+assertEq(classWithNameSetter.name, "classWithNameSetter");
+
+if (typeof reportCompare === "function")
+    reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/Function/function-name-for.js b/js/src/tests/ecma_6/Function/function-name-for.js
new file mode 100644
index 000000000..2f04a5fa8
--- /dev/null
+++ b/js/src/tests/ecma_6/Function/function-name-for.js
@@ -0,0 +1,31 @@
+var BUGNUMBER = 883377;
+var summary = "Anonymous function name should be set based on for-in initializer";
+
+print(BUGNUMBER + ": " + summary);
+
+var exprs = [
+    ["function() {}", false],
+    ["function named() {}", true],
+    ["function*() {}", false],
+    ["function* named() {}", true],
+    ["async function() {}", false],
+    ["async function named() {}", true],
+    ["() => {}", false],
+    ["async () => {}", false],
+    ["class {}", false],
+    ["class named {}", true],
+];
+
+function testForInHead(expr, named) {
+    eval(`
+    for (var forInHead = ${expr} in {}) {
+    }
+    `);
+    assertEq(forInHead.name, named ? "named" : "forInHead");
+}
+for (var [expr, named] of exprs) {
+    testForInHead(expr, named);
+}
+
+if (typeof reportCompare === "function")
+    reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/Function/function-name-method.js b/js/src/tests/ecma_6/Function/function-name-method.js
new file mode 100644
index 000000000..3b2eeee79
--- /dev/null
+++ b/js/src/tests/ecma_6/Function/function-name-method.js
@@ -0,0 +1,70 @@
+var BUGNUMBER = 883377;
+var summary = "Anonymous function name should be set based on method definition";
+
+print(BUGNUMBER + ": " + summary);
+
+var fooSymbol = Symbol("foo");
+var emptySymbol = Symbol("");
+var undefSymbol = Symbol();
+
+function testMethod(prefix, classPrefix="", prototype=false) {
+    var param = (prefix == "set" || prefix == "static set") ? "v" : "";
+    var sep = classPrefix ? "" : ",";
+    var objOrClass = eval(`(${classPrefix}{
+        ${prefix} prop(${param}) {} ${sep}
+        ${prefix} "literal"(${param}) {} ${sep}
+        ${prefix} ""(${param}) {} ${sep}
+        ${prefix} 5(${param}) {} ${sep}
+        ${prefix} [Symbol.iterator](${param}) {} ${sep}
+        ${prefix} [fooSymbol](${param}) {} ${sep}
+        ${prefix} [emptySymbol](${param}) {} ${sep}
+        ${prefix} [undefSymbol](${param}) {} ${sep}
+        ${prefix} [/a/](${param}) {} ${sep}
+    })`);
+
+    var target = prototype ? objOrClass.prototype : objOrClass;
+
+    function testOne(methodName, expectedName) {
+        var f;
+        if (prefix == "get" || prefix == "static get") {
+            f = Object.getOwnPropertyDescriptor(target, methodName).get;
+            expectedName = "get " + expectedName;
+        } else if (prefix == "set" || prefix == "static set") {
+            f = Object.getOwnPropertyDescriptor(target, methodName).set;
+            expectedName = "set " + expectedName;
+        } else {
+            f = Object.getOwnPropertyDescriptor(target, methodName).value;
+        }
+
+        assertEq(f.name, expectedName);
+    }
+    testOne("prop", "prop");
+    testOne("literal", "literal");
+    testOne("", "");
+    testOne(5, "5");
+    testOne(Symbol.iterator, "[Symbol.iterator]");
+    testOne(fooSymbol, "[foo]");
+    testOne(emptySymbol, "[]");
+    testOne(undefSymbol, "");
+    testOne(/a/, "/a/");
+}
+testMethod("");
+testMethod("*");
+testMethod("async");
+testMethod("get");
+testMethod("set");
+
+testMethod("", "class", true);
+testMethod("*", "class", true);
+testMethod("async", "class", true);
+testMethod("get", "class", true);
+testMethod("set", "class", true);
+
+testMethod("static", "class");
+testMethod("static *", "class");
+testMethod("static async", "class");
+testMethod("static get", "class");
+testMethod("static set", "class");
+
+if (typeof reportCompare === "function")
+    reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/Function/function-name-property.js b/js/src/tests/ecma_6/Function/function-name-property.js
new file mode 100644
index 000000000..7ad174b10
--- /dev/null
+++ b/js/src/tests/ecma_6/Function/function-name-property.js
@@ -0,0 +1,58 @@
+var BUGNUMBER = 883377;
+var summary = "Anonymous function name should be set based on property name";
+
+print(BUGNUMBER + ": " + summary);
+
+var fooSymbol = Symbol("foo");
+var emptySymbol = Symbol("");
+var undefSymbol = Symbol();
+
+var exprs = [
+    ["function() {}", false],
+    ["function named() {}", true],
+    ["function*() {}", false],
+    ["function* named() {}", true],
+    ["async function() {}", false],
+    ["async function named() {}", true],
+    ["() => {}", false],
+    ["async () => {}", false],
+    ["class {}", false],
+    ["class named {}", true],
+];
+
+function testPropertyDefinition(expr, named) {
+    var obj = eval(`({
+        prop: ${expr},
+        "literal": ${expr},
+        "": ${expr},
+        5: ${expr},
+        0.4: ${expr},
+        [Symbol.iterator]: ${expr},
+        [fooSymbol]: ${expr},
+        [emptySymbol]: ${expr},
+        [undefSymbol]: ${expr},
+        [/a/]: ${expr},
+    })`);
+    assertEq(obj.prop.name, named ? "named" : "prop");
+    assertEq(obj["literal"].name, named ? "named" : "literal");
+    assertEq(obj[""].name, named ? "named" : "");
+    assertEq(obj[5].name, named ? "named" : "5");
+    assertEq(obj[0.4].name, named ? "named" : "0.4");
+    assertEq(obj[Symbol.iterator].name, named ? "named" : "[Symbol.iterator]");
+    assertEq(obj[fooSymbol].name, named ? "named" : "[foo]");
+    assertEq(obj[emptySymbol].name, named ? "named" : "[]");
+    assertEq(obj[undefSymbol].name, named ? "named" : "");
+    assertEq(obj[/a/].name, named ? "named" : "/a/");
+
+    // Not applicable cases: __proto__.
+    obj = {
+        __proto__: function() {}
+    };
+    assertEq(obj.__proto__.name, "");
+}
+for (var [expr, named] of exprs) {
+    testPropertyDefinition(expr, named);
+}
+
+if (typeof reportCompare === "function")
+    reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/Object/accessor-name.js b/js/src/tests/ecma_6/Object/accessor-name.js
index 1b5268e07..f238a2aef 100644
--- a/js/src/tests/ecma_6/Object/accessor-name.js
+++ b/js/src/tests/ecma_6/Object/accessor-name.js
@@ -27,10 +27,9 @@ o = {get case() { }, set case(v) {}}
 assertEq(name(o, "case", true), "get case");
 assertEq(name(o, "case", false), "set case");
 
-// Congratulations on implementing these!
-assertEq(name({get ["a"]() {}}, "a", true), "");
-assertEq(name({get [123]() {}}, "123", true), "");
-assertEq(name({set ["a"](v) {}}, "a", false), "");
-assertEq(name({set [123](v) {}}, "123", false), "");
+assertEq(name({get ["a"]() {}}, "a", true), "get a");
+assertEq(name({get [123]() {}}, "123", true), "get 123");
+assertEq(name({set ["a"](v) {}}, "a", false), "set a");
+assertEq(name({set [123](v) {}}, "123", false), "set 123");
 
 reportCompare(true, true);
diff --git a/js/src/tests/ecma_6/RegExp/compile-symbol.js b/js/src/tests/ecma_6/RegExp/compile-symbol.js
new file mode 100644
index 000000000..9eea1124c
--- /dev/null
+++ b/js/src/tests/ecma_6/RegExp/compile-symbol.js
@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+for (let sym of [Symbol.iterator, Symbol(), Symbol("description")]) {
+    let re = /a/;
+
+    assertEq(re.source, "a");
+    assertThrowsInstanceOf(() => re.compile(sym), TypeError);
+    assertEq(re.source, "a");
+}
+
+if (typeof reportCompare === 'function')
+    reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/RegExp/constructor-symbol.js b/js/src/tests/ecma_6/RegExp/constructor-symbol.js
new file mode 100644
index 000000000..503d7e5a8
--- /dev/null
+++ b/js/src/tests/ecma_6/RegExp/constructor-symbol.js
@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+for (let sym of [Symbol.iterator, Symbol(), Symbol("description")]) {
+    assertThrowsInstanceOf(() => RegExp(sym), TypeError);
+    assertThrowsInstanceOf(() => new RegExp(sym), TypeError);
+
+    assertThrowsInstanceOf(() => RegExp(sym, "g"), TypeError);
+    assertThrowsInstanceOf(() => new RegExp(sym, "g"), TypeError);
+}
+
+if (typeof reportCompare === 'function')
+    reportCompare(0, 0);
diff --git a/js/src/vm/AsyncFunction.cpp b/js/src/vm/AsyncFunction.cpp
index 1e0c7d7c2..f50c87114 100644
--- a/js/src/vm/AsyncFunction.cpp
+++ b/js/src/vm/AsyncFunction.cpp
@@ -116,7 +116,7 @@ js::WrapAsyncFunctionWithProto(JSContext* cx, HandleFunction unwrapped, HandleOb
     // Create a new function with AsyncFunctionPrototype, reusing the name and
     // the length of `unwrapped`.
 
-    RootedAtom funName(cx, unwrapped->name());
+    RootedAtom funName(cx, unwrapped->explicitName());
     uint16_t length;
     if (!unwrapped->getLength(cx, &length))
         return nullptr;
@@ -130,6 +130,9 @@ js::WrapAsyncFunctionWithProto(JSContext* cx, HandleFunction unwrapped, HandleOb
     if (!wrapped)
         return nullptr;
 
+    if (unwrapped->hasCompileTimeName())
+        wrapped->setCompileTimeName(unwrapped->compileTimeName());
+
     // Link them to each other to make GetWrappedAsyncFunction and
     // GetUnwrappedAsyncFunction work.
     unwrapped->setExtendedSlot(UNWRAPPED_ASYNC_WRAPPED_SLOT, ObjectValue(*wrapped));
diff --git a/js/src/vm/Debugger.cpp b/js/src/vm/Debugger.cpp
index 4d181545f..d16781326 100644
--- a/js/src/vm/Debugger.cpp
+++ b/js/src/vm/Debugger.cpp
@@ -9509,7 +9509,7 @@ DebuggerObject::name() const
 {
     MOZ_ASSERT(isFunction());
 
-    return referent()->as<JSFunction>().name();
+    return referent()->as<JSFunction>().explicitName();
 }
 
 JSAtom*
diff --git a/js/src/vm/GlobalObject.cpp b/js/src/vm/GlobalObject.cpp
index 039be2e32..280548cd6 100644
--- a/js/src/vm/GlobalObject.cpp
+++ b/js/src/vm/GlobalObject.cpp
@@ -802,10 +802,10 @@ GlobalObject::getSelfHostedFunction(JSContext* cx, Handle<GlobalObject*> global,
         return false;
     if (exists) {
         RootedFunction fun(cx, &funVal.toObject().as<JSFunction>());
-        if (fun->name() == name)
+        if (fun->explicitName() == name)
             return true;
 
-        if (fun->name() == selfHostedName) {
+        if (fun->explicitName() == selfHostedName) {
             // This function was initially cloned because it was called by
             // other self-hosted code, so the clone kept its self-hosted name,
             // instead of getting the name it's intended to have in content
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index fbf526ae5..9cba1f4dc 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -282,8 +282,6 @@ MakeDefaultConstructor(JSContext* cx, JSOp op, JSAtom* atom, HandleObject proto)
 
     ctor->setIsConstructor();
     ctor->setIsClassConstructor();
-    if (derived)
-        ctor->setHasRest();
 
     MOZ_ASSERT(ctor->infallibleIsDefaultClassConstructor(cx));
 
@@ -1862,7 +1860,6 @@ CASE(EnableInterruptsPseudoOpcode)
 /* Various 1-byte no-ops. */
 CASE(JSOP_NOP)
 CASE(JSOP_NOP_DESTRUCTURING)
-CASE(JSOP_UNUSED182)
 CASE(JSOP_UNUSED183)
 CASE(JSOP_UNUSED187)
 CASE(JSOP_UNUSED192)
@@ -3484,6 +3481,19 @@ CASE(JSOP_TOASYNC)
 }
 END_CASE(JSOP_TOASYNC)
 
+CASE(JSOP_SETFUNNAME)
+{
+    MOZ_ASSERT(REGS.stackDepth() >= 2);
+    FunctionPrefixKind prefixKind = FunctionPrefixKind(GET_UINT8(REGS.pc));
+    ReservedRooted<Value> name(&rootValue0, REGS.sp[-1]);
+    ReservedRooted<JSFunction*> fun(&rootFunction0, &REGS.sp[-2].toObject().as<JSFunction>());
+    if (!SetFunctionNameIfNoOwnName(cx, fun, name, prefixKind))
+        goto error;
+
+    REGS.sp--;
+}
+END_CASE(JSOP_SETFUNNAME)
+
 CASE(JSOP_CALLEE)
     MOZ_ASSERT(REGS.fp()->isFunctionFrame());
     PUSH_COPY(REGS.fp()->calleev());
@@ -4345,7 +4355,7 @@ js::DefFunOperation(JSContext* cx, HandleScript script, HandleObject envChain,
         parent = parent->enclosingEnvironment();
 
     /* ES5 10.5 (NB: with subsequent errata). */
-    RootedPropertyName name(cx, fun->name()->asPropertyName());
+    RootedPropertyName name(cx, fun->explicitName()->asPropertyName());
 
     RootedShape shape(cx);
     RootedObject pobj(cx);
@@ -4993,7 +5003,7 @@ js::ReportRuntimeLexicalError(JSContext* cx, unsigned errorNumber,
     RootedPropertyName name(cx);
 
     if (op == JSOP_THROWSETCALLEE) {
-        name = script->functionNonDelazifying()->name()->asPropertyName();
+        name = script->functionNonDelazifying()->explicitName()->asPropertyName();
     } else if (IsLocalOp(op)) {
         name = FrameSlotName(script, pc)->asPropertyName();
     } else if (IsAtomOp(op)) {
@@ -5061,8 +5071,8 @@ js::ThrowUninitializedThis(JSContext* cx, AbstractFramePtr frame)
     if (fun->isDerivedClassConstructor()) {
         const char* name = "anonymous";
         JSAutoByteString str;
-        if (fun->name()) {
-            if (!AtomToPrintableString(cx, fun->name(), &str))
+        if (fun->explicitName()) {
+            if (!AtomToPrintableString(cx, fun->explicitName(), &str))
                 return false;
             name = str.ptr();
         }
diff --git a/js/src/vm/Opcodes.h b/js/src/vm/Opcodes.h
index 18ae6f073..f6636004d 100644
--- a/js/src/vm/Opcodes.h
+++ b/js/src/vm/Opcodes.h
@@ -1870,7 +1870,16 @@
      *   Stack: =>
      */ \
     macro(JSOP_POPVARENV,          181, "popvarenv",            NULL,  1,  0,  0,  JOF_BYTE) \
-    macro(JSOP_UNUSED182,     182,"unused182",  NULL,     1,  0,  0,  JOF_BYTE) \
+    /*
+     * Pops the top two values on the stack as 'name' and 'fun', defines the
+     * name of 'fun' to 'name' with prefix if any, and pushes 'fun' back onto
+     * the stack.
+     *   Category: Statements
+     *   Type: Function
+     *   Operands: uint8_t prefixKind
+     *   Stack: fun, name => fun
+     */ \
+    macro(JSOP_SETFUNNAME,    182,"setfunname", NULL,     2,  2,  1,  JOF_UINT8) \
     macro(JSOP_UNUSED183,     183,"unused183",  NULL,     1,  0,  0,  JOF_BYTE) \
     \
     /*
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index 6737e774c..bf49f2268 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -2878,7 +2878,7 @@ CloneObject(JSContext* cx, HandleNativeObject selfHostedObject)
     RootedObject clone(cx);
     if (selfHostedObject->is<JSFunction>()) {
         RootedFunction selfHostedFunction(cx, &selfHostedObject->as<JSFunction>());
-        bool hasName = selfHostedFunction->name() != nullptr;
+        bool hasName = selfHostedFunction->explicitName() != nullptr;
 
         // Arrow functions use the first extended slot for their lexical |this| value.
         MOZ_ASSERT(!selfHostedFunction->isArrow());
@@ -2894,7 +2894,7 @@ CloneObject(JSContext* cx, HandleNativeObject selfHostedObject)
         // self-hosting compartment has to be stored on the clone.
         if (clone && hasName) {
             clone->as<JSFunction>().setExtendedSlot(LAZY_FUNCTION_NAME_SLOT,
-                                                    StringValue(selfHostedFunction->name()));
+                                                    StringValue(selfHostedFunction->explicitName()));
         }
     } else if (selfHostedObject->is<RegExpObject>()) {
         RegExpObject& reobj = selfHostedObject->as<RegExpObject>();
@@ -2977,10 +2977,10 @@ JSRuntime::createLazySelfHostedFunctionClone(JSContext* cx, HandlePropertyName s
         return false;
 
     if (!selfHostedFun->isClassConstructor() && !selfHostedFun->hasGuessedAtom() &&
-        selfHostedFun->name() != selfHostedName)
+        selfHostedFun->explicitName() != selfHostedName)
     {
         MOZ_ASSERT(selfHostedFun->getExtendedSlot(HAS_SELFHOSTED_CANONICAL_NAME_SLOT).toBoolean());
-        funName = selfHostedFun->name();
+        funName = selfHostedFun->explicitName();
     }
 
     fun.set(NewScriptedFunction(cx, nargs, JSFunction::INTERPRETED_LAZY,
@@ -3022,7 +3022,7 @@ JSRuntime::cloneSelfHostedFunctionScript(JSContext* cx, HandlePropertyName name,
     MOZ_ASSERT(!targetFun->isInterpretedLazy());
 
     MOZ_ASSERT(sourceFun->nargs() == targetFun->nargs());
-    MOZ_ASSERT(sourceFun->hasRest() == targetFun->hasRest());
+    MOZ_ASSERT(sourceScript->hasRest() == targetFun->nonLazyScript()->hasRest());
 
     // The target function might have been relazified after its flags changed.
     targetFun->setFlags(targetFun->flags() | sourceFun->flags());
diff --git a/js/src/vm/Stack.cpp b/js/src/vm/Stack.cpp
index 439bb1ed4..87e95c893 100644
--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -85,7 +85,7 @@ InterpreterFrame::isNonGlobalEvalFrame() const
 JSObject*
 InterpreterFrame::createRestParameter(JSContext* cx)
 {
-    MOZ_ASSERT(callee().hasRest());
+    MOZ_ASSERT(script()->hasRest());
     unsigned nformal = callee().nargs() - 1, nactual = numActualArgs();
     unsigned nrest = (nactual > nformal) ? nactual - nformal : 0;
     Value* restvp = argv() + nformal;
diff --git a/js/src/vm/TypeInference.cpp b/js/src/vm/TypeInference.cpp
index 2a7762e4f..3d09c7464 100644
--- a/js/src/vm/TypeInference.cpp
+++ b/js/src/vm/TypeInference.cpp
@@ -4541,7 +4541,7 @@ TypeScript::printTypes(JSContext* cx, HandleScript script) const
             uintptr_t(script.get()), script->filename(), script->lineno());
 
     if (script->functionNonDelazifying()) {
-        if (JSAtom* name = script->functionNonDelazifying()->name())
+        if (JSAtom* name = script->functionNonDelazifying()->explicitName())
             name->dumpCharsNoNewline();
     }
 
diff --git a/js/src/vm/TypedArrayObject.cpp b/js/src/vm/TypedArrayObject.cpp
index 9d4ee94c6..ae97be0de 100644
--- a/js/src/vm/TypedArrayObject.cpp
+++ b/js/src/vm/TypedArrayObject.cpp
@@ -2870,7 +2870,7 @@ bool
 DataViewObject::defineGetter(JSContext* cx, PropertyName* name, HandleNativeObject proto)
 {
     RootedId id(cx, NameToId(name));
-    RootedAtom atom(cx, IdToFunctionName(cx, id, "get"));
+    RootedAtom atom(cx, IdToFunctionName(cx, id, FunctionPrefixKind::Get));
     if (!atom)
         return false;
     unsigned attrs = JSPROP_SHARED | JSPROP_GETTER;
diff --git a/js/src/wasm/AsmJS.cpp b/js/src/wasm/AsmJS.cpp
index 4dbc9b387..b4f41c3d5 100644
--- a/js/src/wasm/AsmJS.cpp
+++ b/js/src/wasm/AsmJS.cpp
@@ -679,7 +679,7 @@ FunctionObject(ParseNode* fn)
 static inline PropertyName*
 FunctionName(ParseNode* fn)
 {
-    if (JSAtom* name = FunctionObject(fn)->name())
+    if (JSAtom* name = FunctionObject(fn)->explicitName())
         return name->asPropertyName();
     return nullptr;
 }
@@ -3249,7 +3249,7 @@ static bool
 CheckFunctionHead(ModuleValidator& m, ParseNode* fn)
 {
     JSFunction* fun = FunctionObject(fn);
-    if (fun->hasRest())
+    if (fn->pn_funbox->hasRest())
         return m.fail(fn, "rest args not allowed");
     if (fun->isExprBody())
         return m.fail(fn, "expression closures not allowed");
@@ -8037,7 +8037,7 @@ TryInstantiate(JSContext* cx, CallArgs args, Module& module, const AsmJSMetadata
 static bool
 HandleInstantiationFailure(JSContext* cx, CallArgs args, const AsmJSMetadata& metadata)
 {
-    RootedAtom name(cx, args.callee().as<JSFunction>().name());
+    RootedAtom name(cx, args.callee().as<JSFunction>().explicitName());
 
     if (cx->isExceptionPending())
         return false;
@@ -8128,7 +8128,7 @@ InstantiateAsmJS(JSContext* cx, unsigned argc, JS::Value* vp)
 static JSFunction*
 NewAsmJSModuleFunction(ExclusiveContext* cx, JSFunction* origFun, HandleObject moduleObj)
 {
-    RootedAtom name(cx, origFun->name());
+    RootedAtom name(cx, origFun->explicitName());
 
     JSFunction::Flags flags = origFun->isLambda() ? JSFunction::ASMJS_LAMBDA_CTOR
                                                   : JSFunction::ASMJS_CTOR;
@@ -8846,7 +8846,7 @@ js::AsmJSModuleToString(JSContext* cx, HandleFunction fun, bool addParenToLambda
     if (!out.append("function "))
         return nullptr;
 
-    if (fun->name() && !out.append(fun->name()))
+    if (fun->explicitName() && !out.append(fun->explicitName()))
         return nullptr;
 
     bool haveSource = source->hasSourceData();
@@ -8894,8 +8894,8 @@ js::AsmJSFunctionToString(JSContext* cx, HandleFunction fun)
 
     if (!haveSource) {
         // asm.js functions can't be anonymous
-        MOZ_ASSERT(fun->name());
-        if (!out.append(fun->name()))
+        MOZ_ASSERT(fun->explicitName());
+        if (!out.append(fun->explicitName()))
             return nullptr;
         if (!out.append("() {\n    [sourceless code]\n}"))
             return nullptr;