[Clang] adjust caret placement for the suggested attribute location for enum class

[a-tarasyuk]

Fixes #163224

---

This patch addresses the issue by correcting the caret insertion location for attributes incorrectly positioned before an enum. The location is now derived from the associated EnumDecl: for named enums, the attribute is placed before the identifier, while for anonymous enum definitions, it is placed before the opening brace, with a fallback to the semicolon when no brace is present.

For example:

  [[nodiscard]] enum class E1 {};

is now suggested as:

  enum class [[nodiscard]] E1 {};

[llvmbot]

@llvm/pr-subscribers-clang

Author: Oleksandr T. (a-tarasyuk)

Changes

Fixes #163224

---

This patch addresses the issue by correcting the caret insertion location for attributes incorrectly positioned before enum class, computing the adjustment from the DeclSpec and using the Lexer to advance past enum and class / struct for scoped enums before selecting the suggested location.

For example:

  [[nodiscard]] enum class E1 {};

is now suggested as:

  enum class [[nodiscard]] E1 {};

---

Full diff: https://github.com/llvm/llvm-project/pull/168092.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Parse/Parser.cpp (+22-20)
• (added) clang/test/FixIt/fixit-cxx0x-attributes.cpp (+30)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 88a05affebf9e..06195b5086a66 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -420,6 +420,8 @@ Improvements to Clang's diagnostics
   or continue (#GH166013)
 - Clang now emits a diagnostic in case `vector_size` or `ext_vector_type`
   attributes are used with a negative size (#GH165463).
+- Clang now provides correct caret placement when attributes appear before
+  `enum class` (#GH163224).
 
 Improvements to Clang's time-trace
 ----------------------------------
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index a6fc676f23a51..5bf366db7f509 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -1100,30 +1100,32 @@ Parser::DeclGroupPtrTy Parser::ParseDeclOrFunctionDefInternal(
   // C99 6.7.2.3p6: Handle "struct-or-union identifier;", "enum { X };"
   // declaration-specifiers init-declarator-list[opt] ';'
   if (Tok.is(tok::semi)) {
-    auto LengthOfTSTToken = [](DeclSpec::TST TKind) {
-      assert(DeclSpec::isDeclRep(TKind));
-      switch(TKind) {
-      case DeclSpec::TST_class:
-        return 5;
-      case DeclSpec::TST_struct:
-        return 6;
-      case DeclSpec::TST_union:
-        return 5;
-      case DeclSpec::TST_enum:
-        return 4;
-      case DeclSpec::TST_interface:
-        return 9;
-      default:
-        llvm_unreachable("we only expect to get the length of the class/struct/union/enum");
+    auto GetAdjustedAttrsLoc = [&]() {
+      auto TKind = DS.getTypeSpecType();
+      if (!DeclSpec::isDeclRep(TKind))
+        return SourceLocation();
+
+      if (TKind == DeclSpec::TST_enum) {
+        const auto *ED = dyn_cast_or_null<EnumDecl>(DS.getRepAsDecl());
+        if (ED && ED->isScoped()) {
+          const auto &SM = Actions.getSourceManager();
+          const auto &LangOpts = Actions.getLangOpts();
+          auto End = Lexer::getLocForEndOfToken(DS.getTypeSpecTypeLoc(),
+                                                /*Offset*/ 0, SM, LangOpts);
+          auto NextToken = Lexer::findNextToken(End, SM, LangOpts);
+          if (NextToken)
+            return NextToken->getEndLoc();
+        }
       }
 
+      const auto &Policy = Actions.getASTContext().getPrintingPolicy();
+      unsigned Offset =
+          StringRef(DeclSpec::getSpecifierName(TKind, Policy)).size();
+      return DS.getTypeSpecTypeLoc().getLocWithOffset(Offset);
     };
+
     // Suggest correct location to fix '[[attrib]] struct' to 'struct [[attrib]]'
-    SourceLocation CorrectLocationForAttributes =
-        DeclSpec::isDeclRep(DS.getTypeSpecType())
-            ? DS.getTypeSpecTypeLoc().getLocWithOffset(
-                  LengthOfTSTToken(DS.getTypeSpecType()))
-            : SourceLocation();
+    SourceLocation CorrectLocationForAttributes = GetAdjustedAttrsLoc();
     ProhibitAttributes(Attrs, CorrectLocationForAttributes);
     ConsumeToken();
     RecordDecl *AnonRecord = nullptr;
diff --git a/clang/test/FixIt/fixit-cxx0x-attributes.cpp b/clang/test/FixIt/fixit-cxx0x-attributes.cpp
new file mode 100644
index 0000000000000..f64b6530efa15
--- /dev/null
+++ b/clang/test/FixIt/fixit-cxx0x-attributes.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: not %clang_cc1 -fsyntax-only -fdiagnostics-parseable-fixits -fno-diagnostics-show-line-numbers %s 2>&1 | FileCheck %s -strict-whitespace
+
+[[nodiscard]] enum class E1 { };
+// expected-error@-1 {{misplaced attributes; expected attributes here}}
+// CHECK: {{^}}{{\[\[}}nodiscard]] enum class E1 { };
+// CHECK: {{^}}~~~~~~~~~~~~~           ^
+// CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:1-[[@LINE-4]]:15}:""
+// CHECK: fix-it:"{{.*}}":{[[@LINE-5]]:25-[[@LINE-5]]:25}:"{{\[\[}}nodiscard]]"
+
+[[nodiscard]] enum struct E2 { };
+// expected-error@-1 {{misplaced attributes; expected attributes here}}
+// CHECK: {{^}}{{\[\[}}nodiscard]] enum struct E2 { };
+// CHECK: {{^}}~~~~~~~~~~~~~            ^
+// CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:1-[[@LINE-4]]:15}:""
+// CHECK: fix-it:"{{.*}}":{[[@LINE-5]]:26-[[@LINE-5]]:26}:"{{\[\[}}nodiscard]]"
+
+[[nodiscard]] enum          class E3 { };
+// expected-error@-1 {{misplaced attributes; expected attributes here}}
+// CHECK: {{^}}{{\[\[}}nodiscard]] enum          class E3 { };
+// CHECK: {{^}}~~~~~~~~~~~~~                    ^
+// CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:1-[[@LINE-4]]:15}:""
+// CHECK: fix-it:"{{.*}}":{[[@LINE-5]]:34-[[@LINE-5]]:34}:"{{\[\[}}nodiscard]]"
+
+[[nodiscard]] enum  /*comment*/ class E4 { };
+// expected-error@-1 {{misplaced attributes; expected attributes here}}
+// CHECK: {{^}}{{\[\[}}nodiscard]] enum  /*comment*/ class E4 { };
+// CHECK: {{^}}~~~~~~~~~~~~~                        ^
+// CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:1-[[@LINE-4]]:15}:""
+// CHECK: fix-it:"{{.*}}":{[[@LINE-5]]:38-[[@LINE-5]]:38}:"{{\[\[}}nodiscard]]"

[erichkeane]

A few nits, + want a few tests, else I think this is about right.

[erichkeane]

1 nit, else LGTM

[github-actions]

🐧 Linux x64 Test Results

• 111723 tests passed
• 4465 tests skipped

✅ The build succeeded and all tests passed.

[AaronBallman]

LGTM!