[clang-format] Fix a bug in annotating StartOfName (#127545)

Also ensure we can break before ClassHeadName like StartOfName.

Fixes #127470

Author: owenca

clang/lib/Format/TokenAnnotator.cpp

@@ -2596,7 +2596,7 @@ class AnnotatingParser {
         (!NextNonComment && !Line.InMacroBody) ||
         (NextNonComment &&
          (NextNonComment->isPointerOrReference() ||
-          NextNonComment->is(tok::string_literal) ||
+          NextNonComment->isOneOf(TT_ClassHeadName, tok::string_literal) ||
           (Line.InPragmaDirective && NextNonComment->is(tok::identifier))))) {
       return false;
     }
@@ -6198,8 +6198,8 @@ bool TokenAnnotator::canBreakBefore(const AnnotatedLine &Line,
                 FormatStyle::PAS_Right &&
             (!Right.Next || Right.Next->isNot(TT_FunctionDeclarationName)));
   }
-  if (Right.isOneOf(TT_StartOfName, TT_FunctionDeclarationName) ||
-      Right.is(tok::kw_operator)) {
+  if (Right.isOneOf(TT_StartOfName, TT_FunctionDeclarationName,
+                    TT_ClassHeadName, tok::kw_operator)) {
     return true;
   }
   if (Left.is(TT_PointerOrReference))

clang/unittests/Format/FormatTest.cpp

@@ -29028,6 +29028,11 @@ TEST_F(FormatTest, WrapNamespaceBodyWithEmptyLinesAlways) {
                Style);
 }
 
+TEST_F(FormatTest, BreakBeforeClassName) {
+  verifyFormat("class ABSL_ATTRIBUTE_TRIVIAL_ABI ABSL_NULLABILITY_COMPATIBLE\n"
+               "    ArenaSafeUniquePtr {};");
+}
+
 } // namespace
 } // namespace test
 } // namespace format

clang/unittests/Format/TokenAnnotatorTest.cpp

@@ -3250,6 +3250,10 @@ TEST_F(TokenAnnotatorTest, StartOfName) {
   EXPECT_TOKEN(Tokens[0], tok::at, TT_ObjCDecl);
   EXPECT_TOKEN(Tokens[2], tok::identifier, TT_StartOfName);
 
+  Tokens = annotate("class FOO BAR C {};");
+  ASSERT_EQ(Tokens.size(), 8u) << Tokens;
+  EXPECT_TOKEN(Tokens[2], tok::identifier, TT_Unknown); // Not StartOfName
+
   auto Style = getLLVMStyle();
   Style.StatementAttributeLikeMacros.push_back("emit");
   Tokens = annotate("emit foo = 0;", Style);