[clang-format] Handle attributes in enum declaration.

[tchatow]

Summary

Fixes https://github.com/llvm/llvm-project/issues/55457

Ensures that attributes in the enum declaration are interpreted
correctly, for instance:

enum class [[nodiscard]] E {
  a,
  b
};

[MyDeveloperDay]

This looks good to me, but let the others chime in..

[curdeius]

Could you please add test cases with non-empty enums both with and without comments please like in the bug report?

[tchatow]

Added tests for non-empty enums

[curdeius]

LGTM. Thanks a lot!
Do you have commit rights or need some help landing this?

[tchatow]

No, I'll need someone to commit it on my behalf.

clang/lib/Format/UnwrappedLineParser.cpp

if (Style.Language == FormatStyle::LK_Proto && FormatTok->is(tok::equal))
     return false;
 
   // Eat up enum class ...
   if (FormatTok->isOneOf(tok::kw_class, tok::kw_struct))
     nextToken();
 
   while (FormatTok->Tok.getIdentifierInfo() ||
          FormatTok->isOneOf(tok::colon, tok::coloncolon, tok::less,
-                            tok::greater, tok::comma, tok::question)) {
+                            tok::greater, tok::comma, tok::question,
+                            tok::l_square, tok::r_square)) {
     nextToken();
     // We can have macros or attributes in between 'enum' and the enum name.
     if (FormatTok->is(tok::l_paren))
       parseParens();
+    if (FormatTok->is(TT_AttributeSquare)) {
+      parseSquare();
+      // Consume the closing TT_AttributeSquare.
+      if (FormatTok->Next && FormatTok->is(TT_AttributeSquare))
+        nextToken();
+    }
     if (FormatTok->is(tok::identifier)) {
       nextToken();
       // If there are two identifiers in a row, this is likely an elaborate
       // return type. In Java, this can be "implements", etc.
       if (Style.isCpp() && FormatTok->is(tok::identifier))
         return false;
     }
   }

clang/unittests/Format/FormatTest.cpp

verifyGoogleFormat("enum {\n"
                      "  Four = (Zero && (One ^ Two)) | (One << Two),\n"
                      "  Five = (One, Two, Three, Four, 5)\n"
                      "};");
   verifyFormat("enum Enum {};");
   verifyFormat("enum {};");
   verifyFormat("enum X E {} d;");
   verifyFormat("enum __attribute__((...)) E {} d;");
   verifyFormat("enum __declspec__((...)) E {} d;");
+  verifyFormat("enum [[nodiscard]] E {} d;");
   verifyFormat("enum {\n"
                "  Bar = Foo<int, int>::value\n"
                "};",
                getLLVMStyleWithColumns(30));
 
   verifyFormat("enum ShortEnum { A, B, C };");
   verifyGoogleFormat("enum ShortEnum { A, B, C };");
 
verifyFormat("enum {\n"
                "        UNSIGNED,\n"
                "        BOOL,\n"
                "        FLOAT,\n"
                "        DOUBLE,\n"
                "        COMPLEX\n"
                "};",
                EightIndent);
 
+  verifyFormat("enum [[nodiscard]] E {\n"
+               "  ONE,\n"
+               "  TWO,\n"
+               "};");
+  verifyFormat("enum [[nodiscard]] E {\n"
+               "  // Comment 1\n"
+               "  ONE,\n"
+               "  // Comment 2\n"
+               "  TWO,\n"
+               "};");
+
   // Not enums.
   verifyFormat("enum X f() {\n"
                "  a();\n"
                "  return 42;\n"
                "}");
   verifyFormat("enum X Type::f() {\n"
                "  a();\n"
                "  return 42;\n"
verifyFormat("enum struct {\n"
                "  Four = (Zero && (One ^ Two)) | (One << Two),\n"
                "  Five = (One, Two, Three, Four, 5)\n"
                "};");
   verifyFormat("enum struct Enum {};");
   verifyFormat("enum struct {};");
   verifyFormat("enum struct X E {} d;");
   verifyFormat("enum struct __attribute__((...)) E {} d;");
   verifyFormat("enum struct __declspec__((...)) E {} d;");
+  verifyFormat("enum struct [[nodiscard]] E {} d;");
   verifyFormat("enum struct X f() {\n  a();\n  return 42;\n}");
+
+  verifyFormat("enum struct [[nodiscard]] E {\n"
+               "  ONE,\n"
+               "  TWO,\n"
+               "};");
+  verifyFormat("enum struct [[nodiscard]] E {\n"
+               "  // Comment 1\n"
+               "  ONE,\n"
+               "  // Comment 2\n"
+               "  TWO,\n"
+               "};");
 }
 
 TEST_F(FormatTest, FormatsEnumClass) {
   verifyFormat("enum class {\n"
                "  Zero,\n"
                "  One = 1,\n"
                "  Two = One + 1,\n"
                "  Three = (One + Two),\n"
                "  Four = (Zero && (One ^ Two)) | (One << Two),\n"
                "  Five = (One, Two, Three, Four, 5)\n"
                "};");
   verifyFormat("enum class Enum {};");
   verifyFormat("enum class {};");
   verifyFormat("enum class X E {} d;");
   verifyFormat("enum class __attribute__((...)) E {} d;");
   verifyFormat("enum class __declspec__((...)) E {} d;");
+  verifyFormat("enum class [[nodiscard]] E {} d;");
   verifyFormat("enum class X f() {\n  a();\n  return 42;\n}");
+
+  verifyFormat("enum class [[nodiscard]] E {\n"
+               "  ONE,\n"
+               "  TWO,\n"
+               "};");
+  verifyFormat("enum class [[nodiscard]] E {\n"
+               "  // Comment 1\n"
+               "  ONE,\n"
+               "  // Comment 2\n"
+               "  TWO,\n"
+               "};");
 }
 
 TEST_F(FormatTest, FormatsEnumTypes) {
   verifyFormat("enum X : int {\n"
                "  A, // Force multiple lines.\n"
                "  B\n"
                "};");
   verifyFormat("enum X : int { A, B };");