[CS] Don't apply compatibility logic to collection literals

lib/Sema/CSApply.cpp

@@ -4045,20 +4045,19 @@ namespace {
     }
 
     Expr *visitCoerceExpr(CoerceExpr *expr) {
+      auto *coerced = visitCoerceExprImpl(expr);
+      if (!coerced)
+        return nullptr;
+
       // If we need to insert a force-unwrap for coercions of the form
       // 'as T!', do so now.
-      if (hasForcedOptionalResult(expr)) {
-        auto *coerced = visitCoerceExpr(expr, None);
-        if (!coerced)
-          return nullptr;
-
-        return forceUnwrapIUO(coerced);
-      }
+      if (hasForcedOptionalResult(expr))
+        coerced = forceUnwrapIUO(coerced);
 
-      return visitCoerceExpr(expr, None);
+      return coerced;
     }
 
-    Expr *visitCoerceExpr(CoerceExpr *expr, Optional<unsigned> choice) {
+    Expr *visitCoerceExprImpl(CoerceExpr *expr) {
       // Simplify and update the type we're coercing to.
       assert(expr->getCastTypeRepr());
       const auto toType = simplifyType(cs.getType(expr->getCastTypeRepr()));
@@ -4107,14 +4106,11 @@ namespace {
       // get it from the solution to determine whether we've picked a coercion
       // or a bridging conversion.
       auto *locator = cs.getConstraintLocator(expr);
-
-      if (!choice) {
-        choice = solution.getDisjunctionChoice(locator);
-      }
+      auto choice = solution.getDisjunctionChoice(locator);
 
       // Handle the coercion/bridging of the underlying subexpression, where
       // optionality has been removed.
-      if (*choice == 0) {
+      if (choice == 0) {
         // Convert the subexpression.
         Expr *sub = expr->getSubExpr();
 
@@ -4128,7 +4124,7 @@ namespace {
       }
 
       // Bridging conversion.
-      assert(*choice == 1 && "should be bridging");
+      assert(choice == 1 && "should be bridging");
 
       // Handle optional bindings.
       Expr *sub = handleOptionalBindings(expr->getSubExpr(), toType,

lib/Sema/CSSimplify.cpp

@@ -9555,16 +9555,35 @@ ConstraintSystem::simplifyBridgingConstraint(Type type1,
   // we generated somewhat reasonable code that performed a force cast. To
   // maintain compatibility with that behavior, allow the coercion between
   // two collections, but add a warning fix telling the user to use as! or as?
-  // instead.
+  // instead. In Swift 6 mode, this becomes an error.
   //
-  // We only need to perform this compatibility logic if the LHS type is a
-  // (potentially optional) type variable, as only such a constraint could have
-  // been previously been left unsolved.
-  //
-  // FIXME: Once we get a new language version, change this condition to only
-  // preserve compatibility for Swift 5.x mode.
-  auto canUseCompatFix =
-      rawType1->lookThroughAllOptionalTypes()->isTypeVariableOrMember();
+  // We only need to perform this compatibility logic if this is a coercion of
+  // something that isn't a collection expr (as collection exprs would have
+  // crashed in codegen due to CSApply peepholing them). Additionally, the LHS
+  // type must be a (potentially optional) type variable, as only such a
+  // constraint could have been previously been left unsolved.
+  auto canUseCompatFix = [&]() {
+    if (Context.isSwiftVersionAtLeast(6))
+      return false;
+
+    if (!rawType1->lookThroughAllOptionalTypes()->isTypeVariableOrMember())
+      return false;
+
+    SmallVector<LocatorPathElt, 4> elts;
+    auto anchor = locator.getLocatorParts(elts);
+    if (!elts.empty())
+      return false;
+
+    auto *coercion = getAsExpr<CoerceExpr>(anchor);
+    if (!coercion)
+      return false;
+
+    auto *subject = coercion->getSubExpr();
+    while (auto *paren = dyn_cast<ParenExpr>(subject))
+      subject = paren->getSubExpr();
+
+    return !isa<CollectionExpr>(subject);
+  }();
 
   // Unless we're allowing the collection compatibility fix, the source cannot
   // be more optional than the destination.

test/Constraints/casts.swift

@@ -280,7 +280,7 @@ func test_coercions_with_overloaded_operator(str: String, optStr: String?, veryO
 
 func id<T>(_ x: T) -> T { x }
 
-func test_compatibility_coercions(_ arr: [Int], _ optArr: [Int]?, _ dict: [String: Int], _ set: Set<Int>) {
+func test_compatibility_coercions(_ arr: [Int], _ optArr: [Int]?, _ dict: [String: Int], _ set: Set<Int>, _ i: Int, _ stringAnyDict: [String: Any]) {
   // Successful coercions don't raise a warning.
   _ = arr as [Any]?
   _ = dict as [String: Int]?
@@ -337,6 +337,24 @@ func test_compatibility_coercions(_ arr: [Int], _ optArr: [Int]?, _ dict: [Strin
 
   // The array can also be inferred to be [Any].
   _ = ([] ?? []) as Array // expected-warning {{left side of nil coalescing operator '??' has non-optional type '[Any]', so the right side is never used}}
+
+  // rdar://88334481 – Don't apply the compatibility logic for collection literals.
+  typealias Magic<T> = T
+  _ = [i] as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  _ = [i] as Magic as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  _ = ([i]) as Magic as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  _  = [i: i] as [String: Any] // expected-error {{cannot convert value of type 'Int' to expected dictionary key type 'String'}}
+  _  = ([i: i]) as [String: Any] // expected-error {{cannot convert value of type 'Int' to expected dictionary key type 'String'}}
+  _  = [i: stringAnyDict] as [String: Any] // expected-error {{cannot convert value of type 'Int' to expected dictionary key type 'String'}}
+
+  // These are currently not peepholed.
+  _ = [i].self as Magic as [String] // expected-warning {{coercion from '[Int]' to '[String]' may fail; use 'as?' or 'as!' instead}}
+  _ = (try [i]) as Magic as [String] // expected-warning {{coercion from '[Int]' to '[String]' may fail; use 'as?' or 'as!' instead}}
+  // expected-warning@-1 {{no calls to throwing functions occur within 'try' expression}}
+
+  // These are wrong, but make sure we don't warn about the value cast always succeeding.
+  _  = [i: i] as! [String: Any]
+  _  = [i: stringAnyDict] as! [String: Any]
 }
 
 // SR-13088

test/Constraints/casts_swift6.swift

@@ -0,0 +1,78 @@
+// RUN: %target-typecheck-verify-swift -enable-objc-interop -swift-version 6
+
+// -swift-version 6 is currently asserts-only
+// REQUIRES: asserts
+
+func id<T>(_ x: T) -> T { x }
+func ohno<T>(_ x: T) -> T? { nil }
+
+// Swift 6 version of the test in casts.swift
+func test_compatibility_coercions(_ arr: [Int], _ optArr: [Int]?, _ dict: [String: Int], _ set: Set<Int>, _ i: Int, _ stringAnyDict: [String: Any]) {
+  // These have always been fine.
+  _ = arr as [Any]?
+  _ = dict as [String: Int]?
+  _ = set as Set<Int>
+
+  // These have always been errors.
+  _ = arr as [String] // expected-error {{cannot convert value of type '[Int]' to type '[String]' in coercion}}
+  // expected-note@-1 {{arguments to generic parameter 'Element' ('Int' and 'String') are expected to be equal}}
+  _ = dict as [String: String] // expected-error {{cannot convert value of type '[String : Int]' to type '[String : String]' in coercion}}
+  // expected-note@-1 {{arguments to generic parameter 'Value' ('Int' and 'String') are expected to be equal}}
+  _ = dict as [String: String]? // expected-error {{'[String : Int]' is not convertible to '[String : String]?'}}
+  // expected-note@-1 {{did you mean to use 'as!' to force downcast?}} {{12-14=as!}}
+  _ = (dict as [String: Int]?) as [String: Int] // expected-error {{value of optional type '[String : Int]?' must be unwrapped to a value of type '[String : Int]'}}
+  // expected-note@-1 {{coalesce using '??' to provide a default when the optional value contains 'nil'}}
+  // expected-note@-2 {{force-unwrap using '!' to abort execution if the optional value contains 'nil'}}
+  _ = set as Set<String>  // expected-error {{cannot convert value of type 'Set<Int>' to type 'Set<String>' in coercion}}
+   // expected-note@-1 {{arguments to generic parameter 'Element' ('Int' and 'String') are expected to be equal}}
+
+  // Make sure we error on the following in Swift 6 mode.
+
+  // FIXME: Bad diagnostics (SR-15843)
+  _ = id(arr) as [String] // expected-error {{type of expression is ambiguous without more context}}
+  _ = (arr ?? []) as [String] // expected-error {{type of expression is ambiguous without more context}}
+  _ = (arr ?? [] ?? []) as [String] // expected-error {{type of expression is ambiguous without more context}}
+  _ = (optArr ?? []) as [String] // expected-error {{type of expression is ambiguous without more context}}
+
+  _ = (arr ?? []) as [String]? // expected-error {{'[Int]' is not convertible to '[String]?'}}
+  // expected-note@-1 {{did you mean to use 'as!' to force downcast?}}
+  _ = (arr ?? []) as [String?]? // expected-error {{'[Int]' is not convertible to '[String?]?'}}
+  // expected-note@-1 {{did you mean to use 'as!' to force downcast?}}
+  _ = (arr ?? []) as [String??]?? // expected-error {{'[Int]' is not convertible to '[String??]??'}}
+  // expected-note@-1 {{did you mean to use 'as!' to force downcast?}}
+  _ = (dict ?? [:]) as [String: String?]? // expected-error {{'[String : Int]' is not convertible to '[String : String?]?'}}
+  // expected-note@-1 {{did you mean to use 'as!' to force downcast?}}
+  _ = (set ?? []) as Set<String>?? // expected-error {{'Set<Int>' is not convertible to 'Set<String>??'}}
+  // expected-note@-1 {{did you mean to use 'as!' to force downcast?}}
+
+  _ = ohno(ohno(ohno(arr))) as [String] // expected-error {{cannot convert value of type '[Int]???' to type '[String]' in coercion}}
+  _ = ohno(ohno(ohno(arr))) as [Int] // expected-error {{cannot convert value of type '[Int]???' to type '[Int]' in coercion}}
+  _ = ohno(ohno(ohno(Set<Int>()))) as Set<String> // expected-error {{cannot convert value of type 'Set<Int>???' to type 'Set<String>' in coercion}}
+  _ = ohno(ohno(ohno(["": ""]))) as [Int: String] // expected-error {{cannot convert value of type '[String : String]???' to type '[Int : String]' in coercion}}
+  _ = ohno(ohno(ohno(dict))) as [String: Int] // expected-error {{cannot convert value of type '[String : Int]???' to type '[String : Int]' in coercion}}
+
+  // In this case the array literal can be inferred to be [String], so totally
+  // valid.
+  _ = ([] ?? []) as [String] // expected-warning {{left side of nil coalescing operator '??' has non-optional type '[String]', so the right side is never used}}
+  _ = (([] as Optional) ?? []) as [String]
+
+  // The array can also be inferred to be [Any].
+  _ = ([] ?? []) as Array // expected-warning {{left side of nil coalescing operator '??' has non-optional type '[Any]', so the right side is never used}}
+
+  // Cases from rdar://88334481
+  typealias Magic<T> = T
+  _ = [i] as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  _ = [i] as Magic as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  _ = ([i]) as Magic as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  _  = [i: i] as [String: Any] // expected-error {{cannot convert value of type 'Int' to expected dictionary key type 'String'}}
+  _  = ([i: i]) as [String: Any] // expected-error {{cannot convert value of type 'Int' to expected dictionary key type 'String'}}
+  _  = [i: stringAnyDict] as [String: Any] // expected-error {{cannot convert value of type 'Int' to expected dictionary key type 'String'}}
+
+  _ = [i].self as Magic as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  _ = (try [i]) as Magic as [String] // expected-error {{cannot convert value of type 'Int' to expected element type 'String'}}
+  // expected-warning@-1 {{no calls to throwing functions occur within 'try' expression}}
+
+  // These are wrong, but make sure we don't warn about the value cast always succeeding.
+  _  = [i: i] as! [String: Any]
+  _  = [i: stringAnyDict] as! [String: Any]
+}

test/SILGen/collection_downcast.swift

@@ -242,8 +242,8 @@ func testSetDowncastBridgedConditional(_ dict: Set<NSObject>)
 
 func promote<T>(_ x: T) -> T? { nil }
 
-// CHECK-LABEL: sil hidden [ossa] @$s19collection_downcast36testCollectionCompatibilityCoercionsyySaySiG_SayypGSgShySSGSDySSSiGtF
-func testCollectionCompatibilityCoercions(_ arr: [Int], _ optArr: [Any]?, _ set: Set<String>, _ dict: [String: Int]) {
+// CHECK-LABEL: sil hidden [ossa] @$s19collection_downcast36testCollectionCompatibilityCoercionsyySaySiG_SayypGSgShySSGSDySSSiGSitF
+func testCollectionCompatibilityCoercions(_ arr: [Int], _ optArr: [Any]?, _ set: Set<String>, _ dict: [String: Int], _ i: Int) {
   // Make sure we generate reasonable code for all of the below examples.
 
   // CHECK: [[CAST_FN:%.+]] = function_ref @$ss15_arrayForceCastySayq_GSayxGr0_lF : $@convention(thin) <τ_0_0, τ_0_1> (@guaranteed Array<τ_0_0>) -> @owned Array<τ_0_1>
@@ -297,4 +297,15 @@ func testCollectionCompatibilityCoercions(_ arr: [Int], _ optArr: [Any]?, _ set:
   // CHECK: [[CAST_FN:%.+]] = function_ref @$ss17_dictionaryUpCastySDyq0_q1_GSDyxq_GSHRzSHR0_r2_lF : $@convention(thin) <τ_0_0, τ_0_1, τ_0_2, τ_0_3 where τ_0_0 : Hashable, τ_0_2 : Hashable> (@guaranteed Dictionary<τ_0_0, τ_0_1>) -> @owned Dictionary<τ_0_2, τ_0_3>
   // CHECK: apply [[CAST_FN]]<String, Int, Int, String>([[DICT]]) : $@convention(thin) <τ_0_0, τ_0_1, τ_0_2, τ_0_3 where τ_0_0 : Hashable, τ_0_2 : Hashable> (@guaranteed Dictionary<τ_0_0, τ_0_1>) -> @owned Dictionary<τ_0_2, τ_0_3>
   _ = promote(promote(promote(dict))) as [Int: String]
+
+  typealias Magic<T> = T
+
+  // These are currently not peepholed.
+  // CHECK: [[CAST_FN:%.+]] = function_ref @$ss15_arrayForceCastySayq_GSayxGr0_lF : $@convention(thin) <τ_0_0, τ_0_1> (@guaranteed Array<τ_0_0>) -> @owned Array<τ_0_1>
+  // CHECK: apply [[CAST_FN]]<Int, String>
+  [i].self as Magic as [String]
+
+  // CHECK: [[CAST_FN:%.+]] = function_ref @$ss15_arrayForceCastySayq_GSayxGr0_lF : $@convention(thin) <τ_0_0, τ_0_1> (@guaranteed Array<τ_0_0>) -> @owned Array<τ_0_1>
+  // CHECK: apply [[CAST_FN]]<Int, String>
+  (try [i]) as Magic as [String]
 }