Bug 1357075 - Pad a nop to unwind to the scope just before a destructuring iterator close trynote

Issue #74

1 files changed, 8 insertions, 0 deletions

diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index b2e48d7ea..4d3b60c2f 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -5318,6 +5318,14 @@ BytecodeEmitter::wrapWithDestructuringIteratorCloseTryNote(int32_t iterDepth, In
 {
     MOZ_ASSERT(this->stackDepth >= iterDepth);
 
+    // Pad a nop at the beginning of the bytecode covered by the trynote so
+    // that when unwinding environments, we may unwind to the scope
+    // corresponding to the pc *before* the start, in case the first bytecode
+    // emitted by |emitter| is the start of an inner scope. See comment above
+    // UnwindEnvironmentToTryPc.
+    if (!emit1(JSOP_TRY_DESTRUCTURING_ITERCLOSE))
+        return false;
+
     ptrdiff_t start = offset();
     if (!emitter(this))
         return false;