[NFC] Fix ImplementsAttr::clone()

Correct an issue with `ImplementsAttr` that would come up if you ever tried to clone an attribute that had been deserialized.

No tests because there’s nothing in the compiler yet that might actually do so.

Author: beccadax

include/swift/AST/Attr.h

@@ -1762,14 +1762,16 @@ class StorageRestrictionsAttr final
 /// The @_implements attribute, which treats a decl as the implementation for
 /// some named protocol requirement (but otherwise not-visible by that name).
 class ImplementsAttr : public DeclAttribute {
-  TypeRepr *TyR;
+  /// If constructed by the \c create() variant with a TypeRepr, the TypeRepr;
+  /// if constructed by the \c create() variant with a DeclContext and
+  /// ProtocolDecl, the DeclContext.
+  llvm::PointerUnion<TypeRepr *, DeclContext *> TyROrDC;
   DeclName MemberName;
   DeclNameLoc MemberNameLoc;
 
   ImplementsAttr(SourceLoc atLoc, SourceRange Range,
-                 TypeRepr *TyR,
-                 DeclName MemberName,
-                 DeclNameLoc MemberNameLoc);
+                 llvm::PointerUnion<TypeRepr *, DeclContext *> TyROrDC,
+                 DeclName MemberName, DeclNameLoc MemberNameLoc);
 
 public:
   static ImplementsAttr *create(ASTContext &Ctx, SourceLoc atLoc,
@@ -1789,7 +1791,9 @@ class ImplementsAttr : public DeclAttribute {
   /// otherwise `nullopt`. This should only be used for dumping.
   std::optional<ProtocolDecl *> getCachedProtocol(DeclContext *dc) const;
 
-  TypeRepr *getProtocolTypeRepr() const { return TyR; }
+  TypeRepr *getProtocolTypeRepr() const {
+    return TyROrDC.dyn_cast<TypeRepr *>();
+  }
 
   DeclName getMemberName() const { return MemberName; }
   DeclNameLoc getMemberNameLoc() const { return MemberNameLoc; }
@@ -1800,8 +1804,12 @@ class ImplementsAttr : public DeclAttribute {
 
   /// Create a copy of this attribute.
   ImplementsAttr *clone(ASTContext &ctx) const {
-    return new (ctx) ImplementsAttr(
-        AtLoc, Range, TyR, getMemberName(), getMemberNameLoc());
+    if (auto tyR = getProtocolTypeRepr()) {
+      return create(ctx, AtLoc, Range, tyR, getMemberName(),
+                    getMemberNameLoc());
+    }
+    auto dc = TyROrDC.dyn_cast<DeclContext *>();
+    return create(dc, getProtocol(dc), getMemberName());
   }
 };
 

lib/AST/Attr.cpp

@@ -2674,11 +2674,12 @@ StorageRestrictionsAttr::create(
                                            /*implicit=*/false);
 }
 
-ImplementsAttr::ImplementsAttr(SourceLoc atLoc, SourceRange range,
-                               TypeRepr *TyR, DeclName MemberName,
-                               DeclNameLoc MemberNameLoc)
+ImplementsAttr::
+ImplementsAttr(SourceLoc atLoc, SourceRange range,
+               llvm::PointerUnion<TypeRepr *, DeclContext *> TyROrDC,
+               DeclName MemberName, DeclNameLoc MemberNameLoc)
     : DeclAttribute(DeclAttrKind::Implements, atLoc, range, /*Implicit=*/false),
-      TyR(TyR), MemberName(MemberName), MemberNameLoc(MemberNameLoc) {}
+      TyROrDC(TyROrDC), MemberName(MemberName), MemberNameLoc(MemberNameLoc) {}
 
 ImplementsAttr *ImplementsAttr::create(ASTContext &Ctx, SourceLoc atLoc,
                                        SourceRange range,
@@ -2695,9 +2696,8 @@ ImplementsAttr *ImplementsAttr::create(DeclContext *DC,
                                        DeclName MemberName) {
   auto &ctx = DC->getASTContext();
   void *mem = ctx.Allocate(sizeof(ImplementsAttr), alignof(ImplementsAttr));
-  auto *attr = new (mem) ImplementsAttr(
-      SourceLoc(), SourceRange(), nullptr,
-      MemberName, DeclNameLoc());
+  auto *attr = new (mem) ImplementsAttr(SourceLoc(), SourceRange(), DC,
+                                        MemberName, DeclNameLoc());
   ctx.evaluator.cacheOutput(ImplementsAttrProtocolRequest{attr, DC},
                             std::move(Proto));
   return attr;