[debugger] fix debug-evaluate wrt shadowed context var.

test/mjsunit/debug-evaluate-shadowed-context.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --expose-debug-as debug --no-analyze-environment-liveness
+
+// Test that debug-evaluate only resolves variables that are used by
+// the function inside which we debug-evaluate. This is to avoid
+// incorrect variable resolution when a context-allocated variable is
+// shadowed by a stack-allocated variable.
+
+Debug = debug.Debug
+
+var exception = null;
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    for (var i = 0; i < exec_state.frameCount() - 1; i++) {
+      var frame = exec_state.frame(i);
+      var value;
+      try {
+        value = frame.evaluate("x").value();
+      } catch (e) {
+        value = e.name;
+      }
+      print(frame.sourceLineText());
+      var expected = frame.sourceLineText().match(/\/\/ (.*$)/)[1];
+      assertEquals(String(expected), String(value));
+    }
+    assertEquals("[object global]",
+                 String(exec_state.frame(0).evaluate("this").value()));
+    exec_state.frame(0).evaluate("y = 'Y'");
+    exec_state.frame(0).evaluate("a = 'A'");
+    assertThrows(() => exec_state.frame(0).evaluate("z"), ReferenceError);
+  } catch (e) {
+    exception = e;
+    print(e + e.stack);
+  }
+}
+
+Debug.setListener(listener);
+
+var a = "a";
+assertEquals("Y", (function() {
+  var x = 1;     // context allocate x
+  (() => x);
+  var y = "y";
+  var z = "z";
+  (function() {
+    var x = 2;   // stack allocate shadowing x
+    (function() {
+      y;         // access y
+      debugger;  // ReferenceError
+    })();        // 2
+  })();          // 1
+  return y;
+})());
+
+assertEquals("A", a);
+a = "a";
+
+assertEquals("Y", (function() {
+  var x = 1;     // context allocate x
+  (() => x);
+  var y = "y";
+  var z = "z";
+  (function() {
+    var x = 2;   // stack allocate shadowing x
+    (() => {
+      y;
+      a;
+      this;      // context allocate receiver
+      debugger;  // ReferenceError
+    })();        // 2
+  })();          // 1
+  return y;
+})());
+
+assertEquals("A", a);
+
+Debug.setListener(null);
+assertNull(exception);