[clang] [clang-format] Harden star and amp annotation (PR #212856)

[Björn Schäpers via cfe-commits]

https://github.com/HazardyKnusperkeks created https://github.com/llvm/llvm-project/pull/212856

At this point we can't (or won't) decide wether this is a template argument or just an expression, opt out of the specialized (and in the test cases wrong) assignment.

Fixes #212622

>From fe953007babfc40f203b914cc23cba21fa6cdf89 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Sch=C3=A4pers?= <schaepers at pas-smt.de>
Date: Wed, 29 Jul 2026 21:39:38 +0200
Subject: [PATCH] [clang-format] Harden star and amp annotation

At this point we can't (or won't) decide wether this is a template
argument or just an expression, opt out of the specialized (and in the
test cases wrong) assignment.

Fixes #212622
---
 clang/lib/Format/UnwrappedLineParser.cpp      | 21 ++++++++++++++++---
 clang/unittests/Format/TokenAnnotatorTest.cpp | 12 +++++++++++
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 8e6f7e2f2ce07..e9061b15c638f 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -2663,7 +2663,8 @@ bool UnwrappedLineParser::parseBracedList(bool IsAngleBracket, bool IsEnum) {
 /// Parses a pair of parentheses (and everything between them).
 /// \param StarAndAmpTokenType If different than TT_Unknown sets this type for
 /// all (double) ampersands and stars. This applies for all nested scopes as
-/// well.
+/// well, this is disabled within a (potential) template argument <>, and thus
+/// also if we find only a <.
 ///
 /// Returns whether there is a `=` token between the parentheses.
 bool UnwrappedLineParser::parseParens(TokenType StarAndAmpTokenType,
@@ -2674,6 +2675,7 @@ bool UnwrappedLineParser::parseParens(TokenType StarAndAmpTokenType,
   bool SeenComma = false;
   bool SeenEqual = false;
   bool MightBeFoldExpr = false;
+  auto ExcessLess = 0;
   nextToken();
   const bool MightBeStmtExpr = FormatTok->is(tok::l_brace);
   if (!InMacroCall && Prev && Prev->is(TT_FunctionLikeMacro))
@@ -2681,8 +2683,10 @@ bool UnwrappedLineParser::parseParens(TokenType StarAndAmpTokenType,
   do {
     switch (FormatTok->Tok.getKind()) {
     case tok::l_paren:
-      if (parseParens(StarAndAmpTokenType, InMacroCall))
+      if (parseParens(ExcessLess == 0 ? StarAndAmpTokenType : TT_Unknown,
+                      InMacroCall)) {
         SeenEqual = true;
+      }
       if (Style.isJava() && FormatTok->is(tok::l_brace))
         parseChildBlock();
       break;
@@ -2799,10 +2803,21 @@ bool UnwrappedLineParser::parseParens(TokenType StarAndAmpTokenType,
     case tok::kw_requires:
       parseRequiresExpression();
       break;
+    case tok::less:
+      // We have here no clue wether this is a less, or a template opener, opt
+      // out of the predefined StarAndAmpTokenType.
+      ++ExcessLess;
+      nextToken();
+      break;
+    case tok::greater:
+      if (ExcessLess > 1)
+        --ExcessLess;
+      nextToken();
+      break;
     case tok::star:
     case tok::amp:
     case tok::ampamp:
-      if (StarAndAmpTokenType != TT_Unknown)
+      if (StarAndAmpTokenType != TT_Unknown && ExcessLess == 0)
         FormatTok->setFinalizedType(StarAndAmpTokenType);
       [[fallthrough]];
     default:
diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
index ad8a4795cd2db..ae9e0b6b8e74c 100644
--- a/clang/unittests/Format/TokenAnnotatorTest.cpp
+++ b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -1579,6 +1579,18 @@ TEST_F(TokenAnnotatorTest, UnderstandsRequiresClausesAndConcepts) {
   ASSERT_EQ(Tokens.size(), 18u) << Tokens;
   EXPECT_TOKEN(Tokens[7], tok::kw_requires, TT_RequiresClause);
   EXPECT_TOKEN(Tokens[12], tok::l_brace, TT_FunctionLBrace);
+
+  Tokens = annotate("template <typename T>\n"
+                    "  requires(is_convertible_v<const T&, Foo>)"
+                    "void foo(T) {}");
+  ASSERT_EQ(Tokens.size(), 24u) << Tokens;
+  EXPECT_TOKEN(Tokens[11], tok::amp, TT_PointerOrReference);
+
+  Tokens = annotate("template <typename T>\n"
+                    "  requires(is_convertible_v<(const T&), Foo>)"
+                    "void foo(T) {}");
+  ASSERT_EQ(Tokens.size(), 26u) << Tokens;
+  EXPECT_TOKEN(Tokens[12], tok::amp, TT_PointerOrReference);
 }
 
 TEST_F(TokenAnnotatorTest, UnderstandsRequiresExpressions) {