GC plugin: improve error reporting when tracing illegal fields.

tools/clang/blink_gc_plugin/DiagnosticsReporter.cpp

Index: tools/clang/blink_gc_plugin/DiagnosticsReporter.cpp
diff --git a/tools/clang/blink_gc_plugin/DiagnosticsReporter.cpp b/tools/clang/blink_gc_plugin/DiagnosticsReporter.cpp
index 0057d80da58cbb89efa25c85720c82f5ebce6ec3..ef3a37d592a39c0f41ce1cfdb56fc89b3ad4c51d 100644
--- a/tools/clang/blink_gc_plugin/DiagnosticsReporter.cpp
+++ b/tools/clang/blink_gc_plugin/DiagnosticsReporter.cpp
@@ -23,9 +23,15 @@ const char kBaseRequiresTracingNote[] =
 const char kFieldsRequireTracing[] =
     "[blink-gc] Class %0 has untraced fields that require tracing.";
 
+const char kFieldsImproperlyTraced[] =
+    "[blink-gc] Class %0 has untraced or not traceable fields.";
+
 const char kFieldRequiresTracingNote[] =
     "[blink-gc] Untraced field %0 declared here:";
 
+const char kFieldShouldNotBeTracedNote[] =
+    "[blink-gc] Untraceable field %0 declared here:";
+
 const char kClassContainsInvalidFields[] =
     "[blink-gc] Class %0 contains invalid fields.";
 
@@ -57,6 +63,9 @@ const char kReferencePtrToGCManagedClassNote[] =
 const char kOwnPtrToGCManagedClassNote[] =
     "[blink-gc] OwnPtr field %0 to a GC managed class declared here:";
 
+const char kUniquePtrToGCManagedClassNote[] =
+    "[blink-gc] std::unique_ptr field %0 to a GC managed class declared here:";
+
 const char kMemberToGCUnmanagedClassNote[] =
     "[blink-gc] Member field %0 to non-GC managed class declared here:";
 
@@ -162,6 +171,8 @@ DiagnosticsReporter::DiagnosticsReporter(
       diagnostic_.getCustomDiagID(getErrorLevel(), kBaseRequiresTracing);
   diag_fields_require_tracing_ =
       diagnostic_.getCustomDiagID(getErrorLevel(), kFieldsRequireTracing);
+  diag_fields_improperly_traced_ =
+      diagnostic_.getCustomDiagID(getErrorLevel(), kFieldsImproperlyTraced);
   diag_class_contains_invalid_fields_ = diagnostic_.getCustomDiagID(
       getErrorLevel(), kClassContainsInvalidFields);
   diag_class_contains_gc_root_ =
@@ -202,6 +213,8 @@ DiagnosticsReporter::DiagnosticsReporter(
       DiagnosticsEngine::Note, kBaseRequiresTracingNote);
   diag_field_requires_tracing_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kFieldRequiresTracingNote);
+  diag_field_should_not_be_traced_note_ = diagnostic_.getCustomDiagID(
+      DiagnosticsEngine::Note, kFieldShouldNotBeTracedNote);
   diag_raw_ptr_to_gc_managed_class_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kRawPtrToGCManagedClassNote);
   diag_ref_ptr_to_gc_managed_class_note_ = diagnostic_.getCustomDiagID(
@@ -210,6 +223,8 @@ DiagnosticsReporter::DiagnosticsReporter(
       DiagnosticsEngine::Note, kReferencePtrToGCManagedClassNote);
   diag_own_ptr_to_gc_managed_class_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kOwnPtrToGCManagedClassNote);
+  diag_unique_ptr_to_gc_managed_class_note_ = diagnostic_.getCustomDiagID(
+      DiagnosticsEngine::Note, kUniquePtrToGCManagedClassNote);
   diag_member_to_gc_unmanaged_class_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kMemberToGCUnmanagedClassNote);
   diag_stack_allocated_field_note_ = diagnostic_.getCustomDiagID(
@@ -279,14 +294,25 @@ void DiagnosticsReporter::BaseRequiresTracing(
       << base << derived->record();
 }
 
-void DiagnosticsReporter::FieldsRequireTracing(
+void DiagnosticsReporter::FieldsImproperlyTraced(
     RecordInfo* info,
     CXXMethodDecl* trace) {
-  ReportDiagnostic(trace->getLocStart(), diag_fields_require_tracing_)
+  // Only mention untraceable in header diagnostic if they appear.
+  unsigned diag = diag_fields_require_tracing_;
+  for (auto& field : info->GetFields()) {
+    if (field.second.IsInproperlyTraced()) {
+      diag = diag_fields_improperly_traced_;
+      break;
+    }
+  }
+  ReportDiagnostic(trace->getLocStart(), diag)
       << info->record();
-  for (auto& field : info->GetFields())
+  for (auto& field : info->GetFields()) {
     if (!field.second.IsProperlyTraced())
       NoteFieldRequiresTracing(info, field.first);
+    if (field.second.IsInproperlyTraced())
+      NoteFieldShouldNotBeTraced(info, field.first);
+  }
 }
 
 void DiagnosticsReporter::ClassContainsInvalidFields(
@@ -307,6 +333,8 @@ void DiagnosticsReporter::ClassContainsInvalidFields(
       note = diag_reference_ptr_to_gc_managed_class_note_;
     } else if (error.second == CheckFieldsVisitor::kOwnPtrToGCManaged) {
       note = diag_own_ptr_to_gc_managed_class_note_;
+    } else if (error.second == CheckFieldsVisitor::kUniquePtrToGCManaged) {
+      note = diag_unique_ptr_to_gc_managed_class_note_;
     } else if (error.second == CheckFieldsVisitor::kMemberToGCUnmanaged) {
       note = diag_member_to_gc_unmanaged_class_note_;
     } else if (error.second == CheckFieldsVisitor::kMemberInUnmanaged) {
@@ -482,6 +510,12 @@ void DiagnosticsReporter::NoteFieldRequiresTracing(
   NoteField(field, diag_field_requires_tracing_note_);
 }
 
+void DiagnosticsReporter::NoteFieldShouldNotBeTraced(
+    RecordInfo* holder,
+    FieldDecl* field) {
+  NoteField(field, diag_field_should_not_be_traced_note_);
+}
+
 void DiagnosticsReporter::NotePartObjectContainsGCRoot(FieldPoint* point) {
   FieldDecl* field = point->field();
   ReportDiagnostic(field->getLocStart(),