[clang-format] Further improve requires clause detection

[HazardyKnusperkeks]

Summary

If there is a typeish token before the requires, it can't be a requires expression.

Fixes https://github.com/llvm/llvm-project/issues/56176

[owenpan]

clang/lib/Format/UnwrappedLineParser.cpp

3163–3169

It's harder to understand with the default case at the top without a break. See below.

3185–3188

How about this instead?

[curdeius]

LGTM with Owen's suggestion.

clang/lib/Format/UnwrappedLineParser.cpp

3185–3188

👍

clang/unittests/Format/TokenAnnotatorTest.cpp

429

[HazardyKnusperkeks]

clang/lib/Format/UnwrappedLineParser.cpp

3185–3188

Didn't want to duplicate the call.

clang/lib/Format/UnwrappedLineParser.cpp

if (!PreviousNonComment ||
       PreviousNonComment->is(TT_RequiresExpressionLBrace)) {
     // If there is no token, or an expression left brace, we are a requires
     // clause within a requires expression.
     parseRequiresClause(RequiresToken);
     return true;
   }
 
   switch (PreviousNonComment->Tok.getKind()) {
+  default:
+    if (!PreviousNonComment->isTypeOrIdentifier()) {
+      // It's an expression.
+      parseRequiresExpression(RequiresToken);
+      return false;
+    }
+    LLVM_FALLTHROUGH;
   case tok::greater:
   case tok::r_paren:
   case tok::kw_noexcept:
   case tok::kw_const:
     // This is a requires clause.
     parseRequiresClause(RequiresToken);
     return true;
   case tok::amp:
   case tok::ampamp: {
     // This can be either:
     // if (... && requires (T t) ...)
     // Or
     // void member(...) && requires (C<T> ...
     // We check the one token before that for a const:
     // void member(...) const && requires (C<T> ...
     auto PrevPrev = PreviousNonComment->getPreviousNonComment();
     if (PrevPrev && PrevPrev->is(tok::kw_const)) {
       parseRequiresClause(RequiresToken);
       return true;
     }
     break;
   }
-  default:
-    // It's an expression.
-    parseRequiresExpression(RequiresToken);
-    return false;
   }
 
   // Now we look forward and try to check if the paren content is a parameter
   // list. The parameters can be cv-qualified and contain references or
   // pointers.
   // So we want basically to check for TYPE NAME, but TYPE can contain all kinds
   // of stuff: typename, const, *, &, &&, ::, identifiers.
 

clang/unittests/Format/TokenAnnotatorTest.cpp

TEST_F(TokenAnnotatorTest, UnderstandsRequiresClausesAndConcepts) {
   ASSERT_EQ(Tokens.size(), 31u) << Tokens;
   EXPECT_TOKEN(Tokens[8], tok::kw_concept, TT_Unknown);
   EXPECT_TOKEN(Tokens[14], tok::less, TT_TemplateOpener);
   EXPECT_TOKEN(Tokens[18], tok::less, TT_TemplateOpener);
   EXPECT_TOKEN(Tokens[20], tok::greater, TT_TemplateCloser);
   EXPECT_TOKEN(Tokens[25], tok::less, TT_TemplateOpener);
   EXPECT_TOKEN(Tokens[27], tok::greater, TT_TemplateCloser);
   EXPECT_TOKEN(Tokens[28], tok::greater, TT_TemplateCloser);
+
+  Tokens = annotate("auto bar() -> int requires(is_integral_v<T>) {}");
+  ASSERT_EQ(Tokens.size(), 16u) << Tokens;
+  EXPECT_TOKEN(Tokens[6], tok::kw_requires, TT_RequiresClause);
+
+  Tokens = annotate("auto bar() -> void requires(is_integral_v<T>) {}");
+  ASSERT_EQ(Tokens.size(), 16u) << Tokens;
+  EXPECT_TOKEN(Tokens[6], tok::kw_requires, TT_RequiresClause);
+
+  Tokens = annotate("auto bar() -> MyType requires(is_integral_v<T>) {}");
+  ASSERT_EQ(Tokens.size(), 16u) << Tokens;
+  EXPECT_TOKEN(Tokens[6], tok::kw_requires, TT_RequiresClause);
+
+  Tokens =
+      annotate("auto bar() -> SOME_MACRO_TYPE requires(is_integral_v<T>) {}");
+  ASSERT_EQ(Tokens.size(), 16u) << Tokens;
+  EXPECT_TOKEN(Tokens[6], tok::kw_requires, TT_RequiresClause);
+
+  Tokens =
+      annotate("auto bar() -> qualified::type requires(is_integral_v<T>) {}");
+  ASSERT_EQ(Tokens.size(), 18u) << Tokens;
+  EXPECT_TOKEN(Tokens[8], tok::kw_requires, TT_RequiresClause);
+
+  Tokens =
+      annotate("auto bar() -> Tempalte<type> requires(is_integral_v<T>) {}");
+  ASSERT_EQ(Tokens.size(), 19u) << Tokens;
+  EXPECT_TOKEN(Tokens[9], tok::kw_requires, TT_RequiresClause);
 }
 
 TEST_F(TokenAnnotatorTest, UnderstandsRequiresExpressions) {
   auto Tokens = annotate("bool b = requires(int i) { i + 5; };");
   ASSERT_EQ(Tokens.size(), 16u) << Tokens;
   EXPECT_TOKEN(Tokens[3], tok::kw_requires, TT_RequiresExpression);
   EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_RequiresExpressionLParen);
   EXPECT_TOKEN(Tokens[8], tok::l_brace, TT_RequiresExpressionLBrace);