[clang-format] Fix parsing of `operator<() {}` (#75144)

Fixes #74876.

During the parsing of `operator<(Foo&) {}`, there was no handling for
the operator<, so it called `consumeToken()` again, causing the
`AnnotationParser::Scopes` to have one additional left brace each time
it tried to parse it, leaving it unbalanced.
Because of this, in the following code:
```cpp
class Foo {
  void operator<(Foo&) {}
  Foo& f;
};
```
The `&` in the reference member, was being interpreted as
`TT_BinaryOperator` instead of `TT_PointerOrReference`.

2 files changed, 15 insertions, 0 deletions

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index febd683..f3551af 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -164,6 +164,10 @@ private:
                TT_OverloadedOperatorLParen))) {
         return false;
       }
+      if (Previous.Previous->is(tok::kw_operator) &&
+          CurrentToken->is(tok::l_paren)) {
+        return false;
+      }
     }
 
     FormatToken *Left = CurrentToken->Previous;
diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
index 65b1f0f..8e69353 100644
--- a/clang/unittests/Format/TokenAnnotatorTest.cpp
+++ b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -298,6 +298,17 @@ TEST_F(TokenAnnotatorTest, UnderstandsUsesOfStarAndAmp) {
   ASSERT_EQ(Tokens.size(), 12u) << Tokens;
   EXPECT_TOKEN(Tokens[2], tok::identifier, TT_TypeName);
   EXPECT_TOKEN(Tokens[3], tok::star, TT_PointerOrReference);
+
+  Tokens = annotate("class Foo {\n"
+                    "  void operator<() {}\n"
+                    "  Foo &f;\n"
+                    "};");
+  ASSERT_EQ(Tokens.size(), 17u) << Tokens;
+  EXPECT_TOKEN(Tokens[4], tok::kw_operator, TT_FunctionDeclarationName);
+  EXPECT_TOKEN(Tokens[5], tok::less, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[6], tok::l_paren, TT_OverloadedOperatorLParen);
+  EXPECT_TOKEN(Tokens[8], tok::l_brace, TT_FunctionLBrace);
+  EXPECT_TOKEN(Tokens[11], tok::amp, TT_PointerOrReference);
 }
 
 TEST_F(TokenAnnotatorTest, UnderstandsUsesOfPlusAndMinus) {