[vm/bytecode] Do not declare receiver variable in closures

While 'this' variable (receiver) is in scope in closures inside
instance methods, closures do not take it as a parameter and they
shouldn't declare a local variable for receiver unless it's captured.

Fixes #38743
Fixes #39285

Change-Id: Ic5c735fd50457a5fb39acb3ec3590964e4dddba3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/124825
Reviewed-by: Régis Crelier <regis@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

Author: alexmarkov

pkg/vm/lib/bytecode/gen_bytecode.dart

@@ -1964,7 +1964,8 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
         asm.localVariableTable
             .recordContextVariable(asm.offset, locals.contextVarIndexInFrame);
       }
-      if (locals.hasReceiver) {
+      if (locals.hasReceiver &&
+          (!isClosure || locals.isCaptured(locals.receiverVar))) {
         _declareLocalVariable(locals.receiverVar, function.fileOffset);
       }
       for (var v in function.positionalParameters) {

runtime/tests/vm/dart/regress_38743_test.dart

@@ -0,0 +1,25 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// VMOptions=--stacktrace_every=1 --deterministic --optimization-counter-threshold=6 --optimization-filter=baz
+
+// Regression test for https://github.com/dart-lang/sdk/issues/38743.
+// Verifies that VM doesn't crash when collecting debugger stack traces in
+// closures inside instance methods.
+
+class A {
+  foo(unusedArg0) {
+    baz() {
+      for (int i = 0; i < 3; ++i) {
+        print('[$i] $unusedArg0');
+      }
+    }
+
+    baz();
+  }
+}
+
+main() {
+  A().foo(null);
+}