Bug 1357075 - Pad a nop to unwind to the scope just before a destructuring iterator close trynote. (r=arai)

js/src/frontend/BytecodeEmitter.cpp

@@ -5470,6 +5470,14 @@ 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;

js/src/jit-test/tests/parser/bug-1357075.js

@@ -0,0 +1,10 @@
+// |jit-test| error: TypeError
+
+var iterable = {};
+var iterator = {
+  return: 1
+};
+iterable[Symbol.iterator] = function() {
+  return iterator;
+};
+for ([ class get {} ().iterator ] of [iterable]) {}

js/src/vm/Interpreter.cpp

@@ -1098,6 +1098,9 @@ js::UnwindEnvironmentToTryPc(JSScript* script, JSTryNote* tn)
     if (tn->kind == JSTRY_CATCH || tn->kind == JSTRY_FINALLY) {
         pc -= JSOP_TRY_LENGTH;
         MOZ_ASSERT(*pc == JSOP_TRY);
+    } else if (tn->kind == JSTRY_DESTRUCTURING_ITERCLOSE) {
+        pc -= JSOP_TRY_DESTRUCTURING_ITERCLOSE_LENGTH;
+        MOZ_ASSERT(*pc == JSOP_TRY_DESTRUCTURING_ITERCLOSE);
     }
     return pc;
 }
@@ -1938,7 +1941,7 @@ CASE(EnableInterruptsPseudoOpcode)
 /* Various 1-byte no-ops. */
 CASE(JSOP_NOP)
 CASE(JSOP_NOP_DESTRUCTURING)
-CASE(JSOP_UNUSED220)
+CASE(JSOP_TRY_DESTRUCTURING_ITERCLOSE)
 CASE(JSOP_UNUSED221)
 CASE(JSOP_UNUSED222)
 CASE(JSOP_UNUSED223)

js/src/vm/Opcodes.h

@@ -2251,7 +2251,16 @@
      *   Stack: obj => obj
      */ \
     macro(JSOP_CHECKISCALLABLE, 219, "checkiscallable", NULL, 2, 1, 1, JOF_UINT8) \
-    macro(JSOP_UNUSED220,     220,"unused220",     NULL,  1,  0,  0,  JOF_BYTE) \
+    \
+    /*
+     * No-op used by the exception unwinder to determine the correct
+     * environment to unwind to when performing IteratorClose due to
+     * destructuring.
+     *   Category: Other
+     *   Operands:
+     *   Stack: =>
+     */ \
+    macro(JSOP_TRY_DESTRUCTURING_ITERCLOSE, 220, "try-destructuring-iterclose", NULL, 1, 0, 0, JOF_BYTE) \
     macro(JSOP_UNUSED221,     221,"unused221",     NULL,  1,  0,  0,  JOF_BYTE) \
     macro(JSOP_UNUSED222,     222,"unused222",     NULL,  1,  0,  0,  JOF_BYTE) \
     macro(JSOP_UNUSED223,     223,"unused223",     NULL,  1,  0,  0,  JOF_BYTE) \