Implement rewind: drop one or more frames from the debugger.

runtime/observatory/tests/service/rewind_optimized_out_test.dart

+// Copyright (c) 2016, 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=--error_on_bad_type --error_on_bad_override
+
+import 'dart:developer';
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'service_test_common.dart';
+import 'test_helper.dart';
+
+const alwaysInline = "AlwaysInline";
+const noInline = "NeverInline";
+
+int LINE_A = 35;
+int LINE_B = 40;
+int LINE_C = 43;
+int LINE_D = 47;
+
+int global = 0;
+
+@noInline
+b3(x) {
+  int sum = 0;
+  try {
+    for (int i = 0; i < x; i++) {
+      sum += x;
+    }
+  } catch (e) {
+    print("caught $e");
+  }
+  if (global >= 100) {
+    debugger();
+  }
+  global = global + 1;  // Line A
+  return sum;
+}
+
+@alwaysInline
+b2(x) => b3(x);  // Line B
+
+@alwaysInline
+b1(x) => b2(x);  // Line C
+
+test() {
+  while (true) {
+    b1(10000);  // Line D
+  }
+}
+
+var tests = [
+  hasStoppedAtBreakpoint,
+  stoppedAtLine(LINE_A),
+
+  (Isolate isolate) async {
+    // We are at our breakpoint with global=100.
+    var result = await isolate.rootLibrary.evaluate('global');
+    print('global is $result');
+    expect(result.type, equals('Instance'));
+    expect(result.valueAsString, equals('100'));
+
+    // Rewind the top stack frame.
+    bool caughtException;
+    try {
+      result = await isolate.rewind(1);
+      expect(false, isTrue, reason:'Unreachable');
+    } on ServerRpcException catch(e) {
+      caughtException = true;
+      expect(e.code, equals(ServerRpcException.kCannotResume));
+      expect(e.message,
+             'Cannot rewind to frame 1 due to conflicting compiler '
+             'optimizations. Run the vm with --no-prune-dead-locals to '
+             'disallow these optimizations. Next valid rewind frame is 4.');
+    }
+    expect(caughtException, isTrue);
+  },
+];
+
+
+main(args) => runIsolateTests(args, tests, testeeConcurrent: test,
+                              extraArgs:
+                              ['--trace-rewind',
+                               '--prune-dead-locals',
+                               '--enable-inlining-annotations',
+                               '--no-background-compilation',
+                               '--optimization-counter-threshold=10']);