[Mac] Redo NSException handling, and generate better stacks for C++ exceptions.

base/mac/call_with_eh_frame_unittest.mm

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/mac/call_with_eh_frame.h"
+
+#import <Foundation/Foundation.h>
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+namespace mac {
+namespace {
+
+class CallWithEHFrameTest : public testing::Test {
+ protected:
+  void ThrowException() {
+    [NSArray arrayWithObject:nil];
+  }
+};
+
+// Catching from within the EHFrame is allowed.
+TEST_F(CallWithEHFrameTest, CatchExceptionHigher) {
+  bool __block saw_exception = false;
+  base::mac::CallWithEHFrame(^{
+    @try {
+      ThrowException();
+    } @catch (NSException* exception) {
+      saw_exception = true;
+    }
+  });
+  EXPECT_TRUE(saw_exception);
+}
+
+// Trying to catch an exception outside the EHFrame is blocked.
+TEST_F(CallWithEHFrameTest, CatchExceptionLower) {
+  auto catch_exception_lower = ^{
+    bool saw_exception = false;
+    @try {
+      base::mac::CallWithEHFrame(^{
+        ThrowException();
+      });
+    } @catch (NSException* exception) {
+      saw_exception = true;
+    }
+    ASSERT_FALSE(saw_exception);

[Scott Hess - ex-Googler, 2015/07/06 22:34:04]

Should this code crash by failing this assertion, or should it crash at the
point of throwing the exception?  If it's the latter case, could the death
regexp be used to verify that it did _not_ get here?

[Robert Sesek, 2015/07/07 22:26:17]

It should crash by throwing the excpetion.

[Scott Hess - ex-Googler, 2015/07/07 22:34:31]

To be clear, what I meant was that this snippet can fail with a crash in two
places, so I was wondering if there were any way to have the death test verify
that it was the right place and not the wrong place.  Perhaps the
exception-not-handled termination output has something unique-ish that the
regexp can match.

[Robert Sesek, 2015/07/07 22:35:55]

No, I don't think so. One is a crash and the other is an assertion failure,
which just changes the exit code from 0 to 1. But I also can't seem to get any
assertion failure to print out a message that I could test for with the
EXPECT_DEATH string matcher.

+  };
+  EXPECT_DEATH(catch_exception_lower(), "");
+}
+
+}  // namespace
+}  // namespace mac
+}  // namespace base