[clang] [clang-format] Allow decltype in requires clause (PR #78847)

[Emilia Kond via cfe-commits]

https://github.com/rymiel created https://github.com/llvm/llvm-project/pull/78847

If clang-format is not sure whether a `requires` keyword starts a requires clause or a requires expression, it looks ahead to see if any token disqualifies it from being a requires clause. Among these tokens was `decltype`, since it fell through the switch.

This patch allows decltype to exist in a require clause.

I'm not 100% sure this change won't have repercussions, but that just means we need more test coverage!

Fixes https://github.com/llvm/llvm-project/issues/78645

>From 79ebbdc60cfa0635c9d889823a8b37710d9a4fb5 Mon Sep 17 00:00:00 2001
From: Emilia Kond <emilia at rymiel.space>
Date: Sat, 20 Jan 2024 15:44:16 +0200
Subject: [PATCH] [clang-format] Allow decltype in requires clause

If clang-format is not sure whether a `requires` keyword starts a
requires clause or a requires expression, it looks ahead to see if any
token disqualifies it from being a requires clause. Among these tokens
was `decltype`, since it fell through the switch.

This patch allows decltype to exist in a require clause.

I'm not 100% sure this change won't have repercussions, but that just means
we need more test coverage!

Fixes https://github.com/llvm/llvm-project/issues/78645
---
 clang/lib/Format/UnwrappedLineParser.cpp      |  1 +
 clang/unittests/Format/TokenAnnotatorTest.cpp | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index c08ce86449b6ea..62a6018580a0d1 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -3433,6 +3433,7 @@ bool clang::format::UnwrappedLineParser::parseRequires() {
     case tok::coloncolon:
       LastWasColonColon = true;
       break;
+    case tok::kw_decltype:
     case tok::identifier:
       if (FoundType && !LastWasColonColon && OpenAngles == 0) {
         FormatTok = Tokens->setPosition(StoredPosition);
diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
index 64b2abac5cce53..3f94c464b41343 100644
--- a/clang/unittests/Format/TokenAnnotatorTest.cpp
+++ b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -1071,6 +1071,16 @@ TEST_F(TokenAnnotatorTest, UnderstandsRequiresClausesAndConcepts) {
                     "concept C = (!Foo<T>) && Bar;");
   ASSERT_EQ(Tokens.size(), 19u) << Tokens;
   EXPECT_TOKEN(Tokens[15], tok::ampamp, TT_BinaryOperator);
+
+  Tokens = annotate("void f() & requires(C<decltype(x)>) {}");
+  ASSERT_EQ(Tokens.size(), 18u) << Tokens;
+  EXPECT_TOKEN(Tokens[4], tok::amp, TT_PointerOrReference);
+  EXPECT_TOKEN(Tokens[5], tok::kw_requires, TT_RequiresClause);
+
+  Tokens = annotate("auto f() -> int& requires(C<decltype(x)>) {}");
+  ASSERT_EQ(Tokens.size(), 20u) << Tokens;
+  EXPECT_TOKEN(Tokens[6], tok::amp, TT_PointerOrReference);
+  EXPECT_TOKEN(Tokens[7], tok::kw_requires, TT_RequiresClause);
 }
 
 TEST_F(TokenAnnotatorTest, UnderstandsRequiresExpressions) {