1216630 - Print class source when calling toString on the constructor.

This is accomplished in the following ways.
LazyScripts and JSScripts now have 4 offsets:
- Source begin and end for the actual source. This is used for lazy parsing.

- toString begin and end for toString. Some kinds of functions, like async, only have a different begin offset. Class constructors have different offsets for both begin and end.

For syntactically present (i.e. non-default) constructors, the class source span is remembered directly on the LazyScript or JSScript. The toString implementation then splices out the substring directly. For default constructors, a new SRC_CLASS SrcNote type is added. It's binary and has as its arguments the begin and end offsets of the class expression or statement. MakeDefaultConstructor reads the note and overrides the cloned self-hosted function's source object. This is probably the least intrusive way to accomplish this.

1 files changed, 9 insertions, 1 deletions

diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index c15d67b7c..c788e0086 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -7846,7 +7846,8 @@ BytecodeEmitter::emitFunction(ParseNode* pn, bool needsProto)
             Rooted<JSObject*> sourceObject(cx, script->sourceObject());
             Rooted<JSScript*> script(cx, JSScript::Create(cx, options, sourceObject,
                                                           funbox->bufStart, funbox->bufEnd,
-                                                          funbox->preludeStart));
+                                                          funbox->preludeStart,
+                                                          funbox->postludeEnd));
             if (!script)
                 return false;
 
@@ -10226,6 +10227,13 @@ BytecodeEmitter::emitClass(ParseNode* pn)
                 return false;
         }
     } else {
+        // In the case of default class constructors, emit the start and end
+        // offsets in the source buffer as source notes so that when we
+        // actually make the constructor during execution, we can give it the
+        // correct toString output.
+        if (!newSrcNote3(SRC_CLASS_SPAN, ptrdiff_t(pn->pn_pos.begin), ptrdiff_t(pn->pn_pos.end)))
+            return false;
+
         JSAtom *name = names ? names->innerBinding()->pn_atom : cx->names().empty;
         if (heritageExpression) {
             if (!emitAtomOp(name, JSOP_DERIVEDCONSTRUCTOR))