clang plugins: default no-members-in-stack-allocated to on

Artifacts can be removed after the clang prebuilt is updated.

Change-Id: I473c22843445745a39d1fc648a7bbcc336631b8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2152329Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Johann Koenig <johannkoenig@google.com>
Cr-Commit-Position: refs/heads/master@{#759880}

third_party/blink/renderer/BUILD.gn

@@ -116,6 +116,7 @@ config("config") {
       "blink-gc-plugin",
     ]
 
+    # TODO(bikineev): Remove when clang pre-built has been updated.
     # Disallow members in stack allocated classes.
     cflags += [
       "-Xclang",

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

@@ -34,7 +34,9 @@ class BlinkGCPluginAction : public PluginASTAction {
       if (arg == "dump-graph") {
         options_.dump_graph = true;
       } else if (arg == "no-members-in-stack-allocated") {
-        options_.no_members_in_stack_allocated = true;
+        // TODO(bikineev): Flag is on by default. Remove after
+        // third_party/blink/renderer/BUILD.gn has been updated.
+        continue;
       } else if (arg == "enable-weak-members-in-unmanaged-classes") {
         options_.enable_weak_members_in_unmanaged_classes = true;
       } else {

tools/clang/blink_gc_plugin/BlinkGCPluginOptions.h

@@ -12,9 +12,6 @@
 struct BlinkGCPluginOptions {
   bool dump_graph = false;
 
-  // If |true|, disallow Member types in stack allocated classes.
-  bool no_members_in_stack_allocated = false;
-
   // Member<T> fields are only permitted in managed classes,
   // something CheckFieldsVisitor verifies, issuing errors if
   // found in unmanaged classes. WeakMember<T> should be treated

tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp

@@ -78,7 +78,6 @@ void CheckFieldsVisitor::AtValue(Value* edge) {
     return;
   }
 
-  if (options_.no_members_in_stack_allocated) {
   // Members/WeakMembers are prohibited if the host is stack allocated, but
   // heap collections with Members are okay.
   if (stack_allocated_host_ && Parent() &&
@@ -89,7 +88,6 @@ void CheckFieldsVisitor::AtValue(Value* edge) {
       return;
     }
   }
-  }
 
   // If in a stack allocated context, be fairly insistent that T in Member<T>
   // is GC allocated, as stack allocated objects do not have a trace()
@@ -117,8 +115,7 @@ void CheckFieldsVisitor::AtValue(Value* edge) {
         current_, InvalidSmartPtr(Parent())));
     return;
   }
-  if (Parent()->IsRawPtr() &&
-      !(stack_allocated_host_ && options_.no_members_in_stack_allocated)) {
+  if (Parent()->IsRawPtr() && !stack_allocated_host_) {
     RawPtr* rawPtr = static_cast<RawPtr*>(Parent());
     Error error = rawPtr->HasReferenceType() ?
         kReferencePtrToGCManaged : kRawPtrToGCManaged;