Merge pull request swiftlang#22783 from slavapestov/fix-swift-4-tuple-arguments-hack

Sema: Fix inconsistent behavior with SE-0110-related compatibility hack

Author: slavapestov

lib/Sema/CSSimplify.cpp

@@ -1184,7 +1184,10 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
           // We somehow let tuple unsplatting function conversions
           // through in some cases in Swift 4, so let's let that
           // continue to work, but only for Swift 4.
-          if (simplified && isa<DeclRefExpr>(simplified)) {
+          if (simplified &&
+              (isa<DeclRefExpr>(simplified) ||
+               isa<OverloadedDeclRefExpr>(simplified) ||
+               isa<UnresolvedDeclRefExpr>(simplified))) {
             implodeParams(func2Params);
           }
         }

test/Compatibility/tuple_arguments_4.swift

@@ -1642,10 +1642,17 @@ public extension Optional {
 }
 
 // https://bugs.swift.org/browse/SR-6837
+
+// FIXME: Can't overlaod local functions so these must be top-level
+func takePairOverload(_ pair: (Int, Int?)) {}
+func takePairOverload(_: () -> ()) {}
+
 do {
   func takeFn(fn: (_ i: Int, _ j: Int?) -> ()) {}
   func takePair(_ pair: (Int, Int?)) {}
   takeFn(fn: takePair) // Allow for -swift-version 4, but not later
+  takeFn(fn: takePairOverload) // Allow for -swift-version 4, but not later
+
   takeFn(fn: { (pair: (Int, Int?)) in } ) // Disallow for -swift-version 4 and later
   // expected-error@-1 {{contextual closure type '(Int, Int?) -> ()' expects 2 arguments, but 1 was used in closure body}}
   takeFn { (pair: (Int, Int?)) in } // Disallow for -swift-version 4 and later

test/Constraints/tuple_arguments.swift

@@ -1645,10 +1645,16 @@ public extension Optional {
 }
 
 // https://bugs.swift.org/browse/SR-6837
+
+// FIXME: Can't overlaod local functions so these must be top-level
+func takePairOverload(_ pair: (Int, Int?)) {} // expected-note {{found this candidate}}
+func takePairOverload(_: () -> ()) {} // expected-note {{found this candidate}}
+
 do {
   func takeFn(fn: (_ i: Int, _ j: Int?) -> ()) {}
   func takePair(_ pair: (Int, Int?)) {}
   takeFn(fn: takePair) // expected-error {{cannot convert value of type '((Int, Int?)) -> ()' to expected argument type '(Int, Int?) -> ()'}}
+  takeFn(fn: takePairOverload) // expected-error {{ambiguous reference to member 'takePairOverload'}}
   takeFn(fn: { (pair: (Int, Int?)) in } ) // Disallow for -swift-version 4 and later
   // expected-error@-1 {{contextual closure type '(Int, Int?) -> ()' expects 2 arguments, but 1 was used in closure body}}
   takeFn { (pair: (Int, Int?)) in } // Disallow for -swift-version 4 and later