[clang-format] [PR34574] Handle [[nodiscard]] attribute in class decl…

…aration

Summary:
https://bugs.llvm.org/show_bug.cgi?id=34574
https://bugs.llvm.org/show_bug.cgi?id=38401

```
template <typename T>
class [[nodiscard]] result
{
  public:
    result(T&&)
    {
    }
};
```

formats incorrectly to

```
template <typename T>
class [[nodiscard]] result{public : result(T &&){}};
```

Reviewed By: krasimir

Subscribers: cfe-commits

Tags: #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D79354

clang/lib/Format/UnwrappedLineParser.cpp

@@ -2399,9 +2399,10 @@ void UnwrappedLineParser::parseRecord(bool ParseAsExpr) {
 
   // The actual identifier can be a nested name specifier, and in macros
   // it is often token-pasted.
+  // An [[attribute]] can be before the identifier.
   while (FormatTok->isOneOf(tok::identifier, tok::coloncolon, tok::hashhash,
                             tok::kw___attribute, tok::kw___declspec,
-                            tok::kw_alignas) ||
+                            tok::kw_alignas, TT_AttributeSquare) ||
          ((Style.Language == FormatStyle::LK_Java ||
            Style.Language == FormatStyle::LK_JavaScript) &&
           FormatTok->isOneOf(tok::period, tok::comma))) {
@@ -2421,8 +2422,16 @@ void UnwrappedLineParser::parseRecord(bool ParseAsExpr) {
         FormatTok->TokenText != FormatTok->TokenText.upper();
     nextToken();
     // We can have macros or attributes in between 'class' and the class name.
-    if (!IsNonMacroIdentifier && FormatTok->Tok.is(tok::l_paren))
-      parseParens();
+    if (!IsNonMacroIdentifier) {
+      if (FormatTok->Tok.is(tok::l_paren)) {
+        parseParens();
+      } else if (FormatTok->is(TT_AttributeSquare)) {
+        parseSquare();
+        // Consume the closing TT_AttributeSquare.
+        if (FormatTok->Next && FormatTok->is(TT_AttributeSquare))
+          nextToken();
+      }
+    }
   }
 
   // Note that parsing away template declarations here leads to incorrectly

clang/unittests/Format/FormatTest.cpp

@@ -7647,6 +7647,10 @@ TEST_F(FormatTest, UnderstandsSquareAttributes) {
   verifyFormat("void f() [[deprecated(\"so sorry\")]];");
   verifyFormat("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n"
                "    [[unused]] aaaaaaaaaaaaaaaaaaaaaaa(int i);");
+  verifyFormat("[[nodiscard]] bool f() { return false; }");
+  verifyFormat("class [[nodiscard]] f {\npublic:\n  f() {}\n}");
+  verifyFormat("class [[deprecated(\"so sorry\")]] f {\npublic:\n  f() {}\n}");
+  verifyFormat("class [[gnu::unused]] f {\npublic:\n  f() {}\n}");
 
   // Make sure we do not mistake attributes for array subscripts.
   verifyFormat("int a() {}\n"