Merge pull request #28827 from DougGregor/type-checker-cast-nserror

Author: swift-ci

lib/Sema/TypeCheckConstraints.cpp

@@ -4453,11 +4453,13 @@ CheckedCastKind TypeChecker::typeCheckCheckedCast(Type fromType,
   // type.  This is handled in the runtime, so it doesn't need a special cast
   // kind.
   if (Context.LangOpts.EnableObjCInterop) {
+    auto nsObject = Context.getNSObjectType();
+    auto nsErrorTy = Context.getNSErrorType();
+
     if (auto errorTypeProto = Context.getProtocol(KnownProtocolKind::Error)) {
       if (!conformsToProtocol(toType, errorTypeProto, dc,
                               ConformanceCheckFlags::InExpression)
                .isInvalid()) {
-        auto nsErrorTy = Context.getNSErrorType();
         if (nsErrorTy) {
           if (isSubtypeOf(fromType, nsErrorTy, dc)
               // Don't mask "always true" warnings if NSError is cast to
@@ -4466,6 +4468,23 @@ CheckedCastKind TypeChecker::typeCheckCheckedCast(Type fromType,
             return CheckedCastKind::ValueCast;
         }
       }
+
+      if (!conformsToProtocol(fromType, errorTypeProto, dc,
+                                     ConformanceCheckFlags::InExpression)
+              .isInvalid()) {
+        // Cast of an error-conforming type to NSError or NSObject.
+        if ((nsObject && toType->isEqual(nsObject)) ||
+             (nsErrorTy && toType->isEqual(nsErrorTy)))
+            return CheckedCastKind::BridgingCoercion;
+      }
+    }
+
+    // Any class-like type could be dynamically cast to NSObject or NSError
+    // via an Error conformance.
+    if (fromType->mayHaveSuperclass() &&
+        ((nsObject && toType->isEqual(nsObject)) ||
+         (nsErrorTy && toType->isEqual(nsErrorTy)))) {
+      return CheckedCastKind::ValueCast;
     }
   }
 

test/Constraints/ErrorBridging.swift

@@ -73,3 +73,24 @@ extension Error {
 func throwErrorCode() throws {
   throw FictionalServerError.meltedDown // expected-error{{thrown error code type 'FictionalServerError.Code' does not conform to 'Error'; construct an 'FictionalServerError' instance}}{{29-29=(}}{{40-40=)}}
 }
+
+class MyErrorClass { }
+extension MyErrorClass: Error { }
+
+class MyClass { }
+
+func testUnknownErrorBridge(cond: Bool, mc: MyClass) -> NSObject? {
+  if cond {
+    return mc as? NSError // okay
+  }
+
+  return mc as? NSObject // okay
+}
+
+func testAlwaysErrorBridge(cond: Bool, mec: MyErrorClass) -> NSObject? {
+  if cond {
+    return mec as? NSError // expected-warning{{conditional cast from 'MyErrorClass}}' to 'NSError' always succeeds
+  }
+
+  return mec as? NSObject // expected-warning{{conditional cast from 'MyErrorClass}}' to 'NSObject' always succeeds
+}