[clang] [clang/AST] Make it possible to use SwiftAttr in type context (PR #108631)

[Henrik G. Olsson via cfe-commits]

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@@ -5125,24 +5127,54 @@ QualType ASTContext::getUnresolvedUsingType(
 
 QualType ASTContext::getAttributedType(attr::Kind attrKind,
                                        QualType modifiedType,
-                                       QualType equivalentType) const {
+                                       QualType equivalentType,
+                                       const Attr *attr) const {
   llvm::FoldingSetNodeID id;
   AttributedType::Profile(id, attrKind, modifiedType, equivalentType);
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hnrklssn wrote:

`AttributedType` is uniqued based on `attrKind`, but not `attr`. So calling this function may return a type with a pointer to a different `Attr` (although of the same kind). Is this a problem? Do we want to fully unique `AttributedType` based on it's `Attr*`?

The other option I believe is to fetch the `Attr*` from `AttributedTypeLoc` (which you can get through the `TypeSourceInfo` from `Decl` or `ExplicitCastExpr`) rather than the `AttributedType`, but doing that for generic expressions gets quite hairy.

https://github.com/llvm/llvm-project/pull/108631