From 331b570329ce52cd169be1ed206ee2dfc06fa716 Mon Sep 17 00:00:00 2001
From: Chris Willmore <cwillmore@apple.com>
Date: Fri, 1 May 2015 08:27:19 +0000
Subject: [PATCH] Remove reverse subtype constraint between Objective-C classes
 when type checking checked cast via bridging. It prevented bridging upcasts
 using 'as!' from typechecking; we should emit an 'as!'->'as' warning instead.

Also, use ExplicitConversion constraint instead of Conversion when
determining whether a checked cast can be carried out unconditionally.
This matches the constraint used after applying the 'as!'->'as' fixit.

(Also, fix the error that was responsible for breaking
the expr/cast/bridged.swift test.)

<rdar://problem/19813772>

Swift SVN r28034
---
 lib/Sema/CSSimplify.cpp           | 17 +++++------------
 lib/Sema/TypeCheckConstraints.cpp |  5 +++--
 test/Constraints/bridging.swift   |  7 +++++++
 test/expr/cast/bridged.swift      | 11 +++++++++--
 4 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/lib/Sema/CSSimplify.cpp b/lib/Sema/CSSimplify.cpp
index 63d00894091..010b411d5a5 100644
--- a/lib/Sema/CSSimplify.cpp
+++ b/lib/Sema/CSSimplify.cpp
@@ -2518,22 +2518,15 @@ ConstraintSystem::simplifyCheckedCastConstraint(
   case CheckedCastKind::BridgeFromObjectiveC: {
     // This existential-to-concrete cast might bridge through an Objective-C
     // class type.
-    if (auto classType = TC.getDynamicBridgedThroughObjCClass(DC, true,
-                                                              fromType,
-                                                              toType)) {
-      // The class we're bridging through must be a subtype of the type we're
-      // coming from.
-      addConstraint(ConstraintKind::Subtype, classType, fromType,
-                    getConstraintLocator(locator));
-      return SolutionKind::Solved;
-    }
-
     Type objCClass = TC.getDynamicBridgedThroughObjCClass(DC, true,
                                                           fromType,
                                                           toType);
     assert(objCClass && "Type must be bridged");
-    addConstraint(ConstraintKind::Subtype, objCClass, fromType,
-                  getConstraintLocator(locator));
+    (void)objCClass;
+    // Otherwise no constraint is necessary; as long as both objCClass and
+    // fromType are Objective-C types, they can't have any open type variables,
+    // and conversion between unrelated classes will be diagnosed in
+    // typeCheckCheckedCast.
     return SolutionKind::Solved;
   }
 
diff --git a/lib/Sema/TypeCheckConstraints.cpp b/lib/Sema/TypeCheckConstraints.cpp
index 4b9cdddf709..b6549f90046 100644
--- a/lib/Sema/TypeCheckConstraints.cpp
+++ b/lib/Sema/TypeCheckConstraints.cpp
@@ -2023,9 +2023,10 @@ CheckedCastKind TypeChecker::typeCheckCheckedCast(Type fromType,
                                  SourceRange diagToRange,
                                  std::function<bool (Type)> convertToType,
                                  bool suppressDiagnostics) {
-  // If the from/to types are equivalent or implicitly convertible,
+  // If the from/to types are equivalent or explicitly convertible,
   // this is a coercion.
-  if (fromType->isEqual(toType) || isConvertibleTo(fromType, toType, dc)) {
+  if (fromType->isEqual(toType) ||
+      isExplicitlyConvertibleTo(fromType, toType, dc)) {
     return CheckedCastKind::Coercion;
   }
 
diff --git a/test/Constraints/bridging.swift b/test/Constraints/bridging.swift
index c77acbbfdf3..01f14e28eba 100644
--- a/test/Constraints/bridging.swift
+++ b/test/Constraints/bridging.swift
@@ -257,3 +257,10 @@ func rdar20029786(ns: NSString?) {
   var s4: String = ns ?? "str" // expected-error{{'NSString' is not implicitly convertible to 'String'; did you mean to use 'as' to explicitly convert?}}{{20-20=(}}{{31-31=) as String}}
   var s5: String = (ns ?? "str") as String // fixed version
 }
+
+// <rdar://problem/19813772> QoI: Using as! instead of as in this case produces really bad diagnostic
+func rdar19813772(nsma: NSMutableArray) {
+  var a1 = nsma as! Array // expected-error{{argument for generic parameter 'T' could not be inferred}}
+  var a2 = nsma as! Array<AnyObject> // expected-warning{{forced cast from 'NSMutableArray' to 'Array<AnyObject>' always succeeds; did you mean to use 'as'?}}
+  var a3 = nsma as Array<AnyObject>
+}
diff --git a/test/expr/cast/bridged.swift b/test/expr/cast/bridged.swift
index 148148837e8..e427e5423e8 100644
--- a/test/expr/cast/bridged.swift
+++ b/test/expr/cast/bridged.swift
@@ -9,6 +9,8 @@ class NSObject { }
 class BridgedClass : NSObject { 
 }
 
+class SubclassOfBridgedClass : BridgedClass { }
+
 struct BridgedStruct : _ObjectiveCBridgeable {
   static func _isBridgedToObjectiveC() -> Bool {
     return true
@@ -67,12 +69,17 @@ func testBridgeDowncastSuperclass(obj: NSObject, objOpt: NSObject?,
 
 func testBridgeDowncastExact(obj: BridgedClass, objOpt: BridgedClass?,
                              objImplicitOpt: BridgedClass!) -> BridgedStruct? {
-  var s1Opt = obj as? BridgedStruct
+  var s1Opt = obj as? BridgedStruct // expected-warning{{conditional cast from 'BridgedClass' to 'BridgedStruct' always succeeds}}
   var s2Opt = objOpt as? BridgedStruct
-  var s3Opt = objImplicitOpt as? BridgedStruct
+  var s3Opt = objImplicitOpt as? BridgedStruct // expected-warning{{conditional cast from 'BridgedClass!' to 'BridgedStruct' always succeeds}}
 }
 
 func testExplicitBridging(var object: BridgedClass, var value: BridgedStruct) {
   object = value as BridgedClass
   value = object as BridgedStruct
 }
+
+func testBridgingFromSubclass(obj: SubclassOfBridgedClass) {
+  var s1 = obj as! BridgedStruct // expected-warning{{forced cast from 'SubclassOfBridgedClass' to 'BridgedStruct' always succeeds; did you mean to use 'as'?}}
+  var s2 = obj as BridgedStruct
+}