[clang-format] Don't count template template parameter as declaration (#95025)

In ContinuationIndenter::mustBreak, a break is required between a
template declaration and the function/class declaration it applies to,
if the template declaration spans multiple lines.

However, this also includes template template parameters, which can
cause extra erroneous line breaks in some declarations.

This patch makes template template parameters not be counted as template
declarations.

Fixes #93793
Fixes #48746

Author: rymiel

clang/lib/Format/TokenAnnotator.cpp

@@ -127,7 +127,7 @@ class AnnotatingParser {
                    SmallVector<ScopeType> &Scopes)
       : Style(Style), Line(Line), CurrentToken(Line.First), AutoFound(false),
         IsCpp(Style.isCpp()), LangOpts(getFormattingLangOpts(Style)),
-        Keywords(Keywords), Scopes(Scopes) {
+        Keywords(Keywords), Scopes(Scopes), TemplateDeclarationDepth(0) {
     assert(IsCpp == LangOpts.CXXOperatorNames);
     Contexts.push_back(Context(tok::unknown, 1, /*IsExpression=*/false));
     resetTokenMetadata();
@@ -1266,16 +1266,22 @@ class AnnotatingParser {
   }
 
   bool parseTemplateDeclaration() {
-    if (CurrentToken && CurrentToken->is(tok::less)) {
-      CurrentToken->setType(TT_TemplateOpener);
-      next();
-      if (!parseAngle())
-        return false;
-      if (CurrentToken)
-        CurrentToken->Previous->ClosesTemplateDeclaration = true;
-      return true;
-    }
-    return false;
+    if (!CurrentToken || CurrentToken->isNot(tok::less))
+      return false;
+
+    CurrentToken->setType(TT_TemplateOpener);
+    next();
+
+    TemplateDeclarationDepth++;
+    const bool WellFormed = parseAngle();
+    TemplateDeclarationDepth--;
+    if (!WellFormed)
+      return false;
+
+    if (CurrentToken && TemplateDeclarationDepth == 0)
+      CurrentToken->Previous->ClosesTemplateDeclaration = true;
+
+    return true;
   }
 
   bool consumeToken() {
@@ -3091,6 +3097,8 @@ class AnnotatingParser {
   // same decision irrespective of the decisions for tokens leading up to it.
   // Store this information to prevent this from causing exponential runtime.
   llvm::SmallPtrSet<FormatToken *, 16> NonTemplateLess;
+
+  int TemplateDeclarationDepth;
 };
 
 static const int PrecedenceUnaryOperator = prec::PointerToMember + 1;

clang/unittests/Format/TokenAnnotatorTest.cpp

@@ -584,6 +584,23 @@ TEST_F(TokenAnnotatorTest, UnderstandsNonTemplateAngleBrackets) {
   EXPECT_TOKEN(Tokens[20], tok::greater, TT_BinaryOperator);
 }
 
+TEST_F(TokenAnnotatorTest, UnderstandsTemplateTemplateParameters) {
+  auto Tokens = annotate("template <template <typename...> typename X,\n"
+                         "          template <typename...> class Y,\n"
+                         "          typename... T>\n"
+                         "class A {};");
+  ASSERT_EQ(Tokens.size(), 28u) << Tokens;
+  EXPECT_TOKEN(Tokens[1], tok::less, TT_TemplateOpener);
+  EXPECT_TOKEN(Tokens[3], tok::less, TT_TemplateOpener);
+  EXPECT_TOKEN(Tokens[6], tok::greater, TT_TemplateCloser);
+  EXPECT_FALSE(Tokens[6]->ClosesTemplateDeclaration);
+  EXPECT_TOKEN(Tokens[11], tok::less, TT_TemplateOpener);
+  EXPECT_TOKEN(Tokens[14], tok::greater, TT_TemplateCloser);
+  EXPECT_FALSE(Tokens[14]->ClosesTemplateDeclaration);
+  EXPECT_TOKEN(Tokens[21], tok::greater, TT_TemplateCloser);
+  EXPECT_TRUE(Tokens[21]->ClosesTemplateDeclaration);
+}
+
 TEST_F(TokenAnnotatorTest, UnderstandsWhitespaceSensitiveMacros) {
   FormatStyle Style = getLLVMStyle();
   Style.WhitespaceSensitiveMacros.push_back("FOO");