[clang-format] Correctly format lambdas with variadic template parameters.

Fixes https://github.com/llvm/llvm-project/issues/53405.

Reviewed By: MyDeveloperDay, owenpan

Differential Revision: https://reviews.llvm.org/D118220

2 files changed, 40 insertions, 4 deletions

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index ff3e791..b0588d9 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1856,6 +1856,7 @@ bool UnwrappedLineParser::tryToParseLambda() {
     return false;
 
   bool SeenArrow = false;
+  bool InTemplateParameterList = false;
 
   while (FormatTok->isNot(tok::l_brace)) {
     if (FormatTok->isSimpleTypeSpecifier()) {
@@ -1871,6 +1872,14 @@ bool UnwrappedLineParser::tryToParseLambda() {
     case tok::l_square:
       parseSquare();
       break;
+    case tok::kw_class:
+    case tok::kw_template:
+    case tok::kw_typename:
+      assert(FormatTok->Previous);
+      if (FormatTok->Previous->is(tok::less))
+        InTemplateParameterList = true;
+      nextToken();
+      break;
     case tok::amp:
     case tok::star:
     case tok::kw_const:
@@ -1880,11 +1889,8 @@ bool UnwrappedLineParser::tryToParseLambda() {
     case tok::identifier:
     case tok::numeric_constant:
     case tok::coloncolon:
-    case tok::kw_class:
     case tok::kw_mutable:
     case tok::kw_noexcept:
-    case tok::kw_template:
-    case tok::kw_typename:
       nextToken();
       break;
     // Specialization of a template with an integer parameter can contain
@@ -1921,7 +1927,7 @@ bool UnwrappedLineParser::tryToParseLambda() {
     case tok::ellipsis:
     case tok::kw_true:
     case tok::kw_false:
-      if (SeenArrow) {
+      if (SeenArrow || InTemplateParameterList) {
         nextToken();
         break;
       }
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index c45869f..9185de0 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -20560,6 +20560,36 @@ TEST_F(FormatTest, FormatsLambdas) {
   // Lambdas with explicit template argument lists.
   verifyFormat(
       "auto L = []<template <typename> class T, class U>(T<U> &&a) {};\n");
+  verifyFormat("auto L = []<class T>(T) {\n"
+               "  {\n"
+               "    f();\n"
+               "    g();\n"
+               "  }\n"
+               "};\n");
+  verifyFormat("auto L = []<class... T>(T...) {\n"
+               "  {\n"
+               "    f();\n"
+               "    g();\n"
+               "  }\n"
+               "};\n");
+  verifyFormat("auto L = []<typename... T>(T...) {\n"
+               "  {\n"
+               "    f();\n"
+               "    g();\n"
+               "  }\n"
+               "};\n");
+  verifyFormat("auto L = []<template <typename...> class T>(T...) {\n"
+               "  {\n"
+               "    f();\n"
+               "    g();\n"
+               "  }\n"
+               "};\n");
+  verifyFormat("auto L = []</*comment*/ class... T>(T...) {\n"
+               "  {\n"
+               "    f();\n"
+               "    g();\n"
+               "  }\n"
+               "};\n");
 
   // Multiple lambdas in the same parentheses change indentation rules. These
   // lambdas are forced to start on new lines.