Blink GC plugin: Require that fields are actually traced by the visitor and identify tracing of dep…

Blink GC plugin: Require that fields are actually traced by the visitor and identify tracing of dependently-templated base classes.

Prior to this we only required that fields occurred within the trace method.
Thus we would accept seemingly correct code such as:
  m_foo->trace(visitor)
which can result in a dangling pointer.

BUG=395036, 334149
R=haraken@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287310

[zerny-chromium, 2014-07-31 14:58:05]

I've implemented stronger checks for tracing of fields and updated to support
templated base classes. The resulting code is not very nice as it becomes a
series of special cases.
It might be possible to simplify it somehow but I don't see how. The main issue
is that when traversing the AST (Expr/Stmt/etc) the templated AST is not
instantiated with concrete types and so lots of cases become
dependent/unresolved. In most cases we don't care about what instantiations
occur, only that, eg, there is a call to a super class of the right name, ie,
that it is syntactically the same. Thus I've used string comparisons to
implement various cases.

PTAL.

[haraken, 2014-07-31 15:37:11]

LGTM

I don't fully understand special-casings in this CL, but this is just a plugin
for code validation, so we can iterate on them when we encounter problems.

https://codereview.chromium.org/430213003/diff/1/tools/clang/blink_gc_plugin/...
File tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp (right):

https://codereview.chromium.org/430213003/diff/1/tools/clang/blink_gc_plugin/...
tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp:381: // It is unknown if the
member resolves to a method so we string compare.

we string compare => we compare strings

[zerny-chromium, 2014-08-01 07:08:07]

The CQ bit was checked by zerny@chromium.org

[commit-bot: I haz the power, 2014-08-01 07:10:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/zerny@chromium.org/430213003/20001

[zerny-chromium, 2014-08-01 07:28:47]

The CQ bit was unchecked by zerny@chromium.org

[zerny-chromium, 2014-08-01 10:34:01]

Thanks for the reviews. Now that a field occurrence is not sufficient we need to
support tracing via the TraceIfNeeded<T> trait. Looking at this now.

[zerny-chromium, 2014-08-04 07:37:28]

Updated with support for TraceIfNeeded and tried to clean up the code a bit.
PTAL

[haraken, 2014-08-04 08:12:50]

LGTM

[zerny-chromium, 2014-08-04 08:35:17]

The CQ bit was checked by zerny@chromium.org

[commit-bot: I haz the power, 2014-08-04 08:36:04]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/zerny@chromium.org/430213003/40001

[commit-bot: I haz the power, 2014-08-04 09:52:13]

Change committed as 287310