[clang] [clang] Centralize common checks for type attributes (PR #227421)

[Tom Honermann via cfe-commits]

================
@@ -1668,6 +1656,25 @@ static bool checkCommonAttributeFeatures(Sema &S, const Ty *Node,
   return false;
 }
 
+template <typename Ty>
+static bool checkCommonAttributeFeatures(Sema &S, const Ty *Node,
+                                         const ParsedAttr &A,
+                                         bool SkipArgCountCheck) {
+  // Run the checks shared with type attributes (language options, target, and
+  // argument count). This also bails on unknown and ignored attributes.
+  if (checkCommonAttributeFeatures(S, A, SkipArgCountCheck))
+    return true;
+  // Check whether the attribute appertains to the given subject.
+  if (!A.diagnoseAppertainsTo(S, Node))
+    return true;
+  // Check whether the attribute is mutually exclusive with other attributes
+  // that have already been applied to the declaration.
+  if (!A.diagnoseMutualExclusion(S, Node))
+    return true;
----------------
tahonermann wrote:

> I spend some time looking at this and I think adding appertainment support for types is a bigger task and warrants its own PR.

I agree. I don't see sufficient motivation for us to take that on; not any time soon anyway.

> I am leaning towards centralizing the checks we can ...

I agree with this too. The direction of the PR is good. Adding additional overloads of `diagnoseAppertainsTo()` and `diagnoseMutualExclusion()` that accept a `QualType` will avoid the refactoring of `checkCommonAttributeFeatures()` while allowing for future extension. In the meantime, those new functions can just be stubs with a comment like the existing one for the `diagnoseMutualExclusion(class Sema &S, const Stmt *St)` overload in `clang/include/clang/Sema/ParsedAttr.h`.

https://github.com/llvm/llvm-project/pull/227421