Use mapSignatureFunctionType on SubscriptDecls

Author: Jumhyn

lib/AST/Decl.cpp

@@ -2226,6 +2226,15 @@ static Type mapSignatureFunctionType(ASTContext &ctx, Type type,
                                      bool isMethod,
                                      bool isInitializer,
                                      unsigned curryLevels) {
+  if (auto errorType = type->getAs<ErrorType>()) {
+    if (auto originalType = errorType->getOriginalType()) {
+      return ErrorType::get(mapSignatureFunctionType(
+        ctx, originalType, topLevelFunction, isMethod, isInitializer,
+        curryLevels));
+    }
+    return type;
+  }
+
   if (curryLevels == 0) {
     // In an initializer, ignore optionality.
     if (isInitializer) {
@@ -2316,7 +2325,12 @@ CanType ValueDecl::getOverloadSignatureType() const {
     if (isa<VarDecl>(this)) {
       defaultSignatureType = TupleType::getEmpty(getASTContext());
     } else {
-      defaultSignatureType = getInterfaceType()->getCanonicalType();
+      defaultSignatureType = mapSignatureFunctionType(
+          getASTContext(), getInterfaceType(),
+          /*topLevelFunction=*/true,
+          /*isMethod=*/true,
+          /*isInitializer=*/false,
+          1)->getCanonicalType();
     }
 
     // We want to curry the default signature type with the 'self' type of the

test/decl/overload.swift

@@ -258,6 +258,16 @@ struct Subscript3 {
   subscript(x x: Int) -> String { return "" }
 }
 
+struct Subscript4 {
+    subscript(f: @escaping (Int) -> Int) -> Int { // expected-note{{previously declared here}}
+        get { return f(0) }
+    }
+
+    subscript(f: (Int) -> Int) -> Int { // expected-error{{invalid redeclaration of 'subscript(_:)'}}
+        get { return f(0) }
+    }
+}
+
 struct GenericSubscripts {
   subscript<T>(x: T) -> Int { return 0 } // expected-note{{previously declared here}}
 }