IUO: Update decl checking for result type optionality differences.

A previous commit handled parameters but missed handling result
types. As with that commit, we need to pay attention to the IUO
attribute on the decl rather than just concerning ourselves with the
types.

Author: rudkx

lib/Sema/TypeCheckDecl.cpp

@@ -4373,6 +4373,13 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
     validateAttributes(TC, SD);
 
+    auto *TyR = SD->getElementTypeLoc().getTypeRepr();
+    if (TyR && TyR->getKind() == TypeReprKind::ImplicitlyUnwrappedOptional) {
+      auto &C = SD->getASTContext();
+      SD->getAttrs().add(
+          new (C) ImplicitlyUnwrappedOptionalAttr(/* implicit= */ true));
+    }
+
     if (!checkOverrides(TC, SD)) {
       // If a subscript has an override attribute but does not override
       // anything, complain.
@@ -4415,13 +4422,6 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       synthesizeSetterForMutableAddressedStorage(SD, TC);
     }
 
-    auto *TyR = SD->getElementTypeLoc().getTypeRepr();
-    if (TyR && TyR->getKind() == TypeReprKind::ImplicitlyUnwrappedOptional) {
-      auto &C = SD->getASTContext();
-      SD->getAttrs().add(
-          new (C) ImplicitlyUnwrappedOptionalAttr(/* implicit= */ true));
-    }
-
     TC.checkDeclAttributes(SD);
   }
 
@@ -5746,7 +5746,11 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
       TypeRepr *TR = resultTL.getTypeRepr();
 
-      if (resultOTK == OTK_Optional || treatIUOResultAsError) {
+      bool resultIsPlainOptional = resultOTK == OTK_Optional;
+      if (member->getAttrs().hasAttribute<ImplicitlyUnwrappedOptionalAttr>())
+        resultIsPlainOptional = false;
+
+      if (resultIsPlainOptional || treatIUOResultAsError) {
         if (parentResultTy->getAnyOptionalObjectType())
           return;
         emittedError = true;
@@ -6119,7 +6123,13 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
         auto canDeclTy = declTy->getCanonicalType(genericSig);
         auto canParentDeclTy = parentDeclTy->getCanonicalType(genericSig);
 
-        if (canDeclTy == canParentDeclTy) {
+        auto declIUOAttr =
+            decl->getAttrs().hasAttribute<ImplicitlyUnwrappedOptionalAttr>();
+        auto parentDeclIUOAttr =
+            parentDecl->getAttrs()
+                .hasAttribute<ImplicitlyUnwrappedOptionalAttr>();
+
+        if (declIUOAttr == parentDeclIUOAttr && canDeclTy == canParentDeclTy) {
           matches.push_back({parentDecl, true, parentDeclTy});
           hadExactMatch = true;
           continue;
@@ -6321,8 +6331,13 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
         (attempt == OverrideCheckingAttempt::MismatchedOptional ||
          attempt == OverrideCheckingAttempt::BaseNameWithMismatchedOptional);
 
+    auto declIUOAttr =
+        decl->getAttrs().hasAttribute<ImplicitlyUnwrappedOptionalAttr>();
+    auto matchDeclIUOAttr =
+        matchDecl->getAttrs().hasAttribute<ImplicitlyUnwrappedOptionalAttr>();
+
     // If this is an exact type match, we're successful!
-    if (declTy->isEqual(matchType)) {
+    if (declIUOAttr == matchDeclIUOAttr && declTy->isEqual(matchType)) {
       // Nothing to do.
 
     } else if (method) {