Merge pull request swiftlang#22719 from xedin/rdar-48114578

[CSApply] Account for failures in argument application of unresolved …

Author: xedin

lib/Sema/CSApply.cpp

@@ -2444,8 +2444,16 @@ namespace {
             expr->getArgumentLabelLocs(), expr->hasTrailingClosure(),
             /*implicit=*/expr->isImplicit(), Type(), getType);
         result = finishApply(apply, Type(), cs.getConstraintLocator(expr));
+
+        // FIXME: Application could fail, because some of the solutions
+        // are not expressible in AST (yet?), like certain tuple-to-tuple
+        // conversions. Better solution here would be not to form solutions
+        // which couldn't be applied by e.g. detecting situations like that
+        // and inserting fixes early.
+        if (!result)
+          return nullptr;
       }
-			
+
       // Check for ambiguous member if the base is an Optional
       if (baseTy->getOptionalObjectType()) {
         diagnoseAmbiguousNominalMember(baseTy, result);

test/Constraints/members.swift

@@ -517,3 +517,25 @@ func rdar46211109() {
   let _: MyIntSequenceStruct? = foo(Int.Self)
   // expected-error@-1 {{type 'Int' has no member 'Self'}}
 }
+
+func rdar_48114578() {
+  struct S<T> {
+    var value: T
+
+    static func valueOf<T>(_ v: T) -> S<T> {
+      return S<T>(value: v)
+    }
+  }
+
+  typealias A = (a: [String]?, b: Int)
+
+  func foo(_ a: [String], _ b: Int) -> S<A> {
+    let v = (a, b)
+    return .valueOf(v)
+    // expected-error@-1 {{cannot express tuple conversion '([String], Int)' to '(a: [String]?, b: Int)'}}
+  }
+
+  func bar(_ a: [String], _ b: Int) -> S<A> {
+    return .valueOf((a, b)) // Ok
+  }
+}