[clang-format] Correctly annotate RequiresExpressionLBrace (llvm#155773)

Fixes llvm#155746

(cherry picked from commit c62a5bf)

Author: owenca

clang/lib/Format/TokenAnnotator.cpp

@@ -4007,7 +4007,7 @@ void TokenAnnotator::calculateFormattingInformation(AnnotatedLine &Line) const {
     auto *Tok = Line.Last->Previous;
     while (Tok->isNot(tok::r_brace))
       Tok = Tok->Previous;
-    if (auto *LBrace = Tok->MatchingParen; LBrace) {
+    if (auto *LBrace = Tok->MatchingParen; LBrace && LBrace->is(TT_Unknown)) {
       assert(LBrace->is(tok::l_brace));
       Tok->setBlockKind(BK_Block);
       LBrace->setBlockKind(BK_Block);

clang/unittests/Format/TokenAnnotatorTest.cpp

@@ -1349,6 +1349,14 @@ TEST_F(TokenAnnotatorTest, UnderstandsRequiresClausesAndConcepts) {
   EXPECT_EQ(Tokens[21]->MatchingParen, Tokens[15]);
   EXPECT_TRUE(Tokens[21]->ClosesRequiresClause);
 
+  Tokens = annotate("template <typename Foo>\n"
+                    "void Fun(const Foo &F)\n"
+                    "  requires requires(Foo F) {\n"
+                    "    { F.Bar() } -> std::same_as<int>;\n"
+                    "  };");
+  ASSERT_EQ(Tokens.size(), 38u) << Tokens;
+  EXPECT_TOKEN(Tokens[19], tok::l_brace, TT_RequiresExpressionLBrace);
+
   Tokens =
       annotate("template <class A, class B> concept C ="
                "std::same_as<std::iter_value_t<A>, std::iter_value_t<B>>;");