Merge pull request swiftlang#39209 from xedin/rdar-81228501

[Diagnostics] Ignore warnings while diagnosing ambiguities

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -3990,8 +3990,14 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
 
   llvm::SmallSetVector<FixInContext, 4> fixes;
   for (auto &solution : solutions) {
-    for (auto *fix : solution.Fixes)
+    for (auto *fix : solution.Fixes) {
+      // Ignore warnings in favor of actual error fixes,
+      // because they are not the source of ambiguity/failures.
+      if (fix->isWarning())
+        continue;
+
       fixes.insert({&solution, fix});
+    }
   }
 
   llvm::MapVector<ConstraintLocator *, SmallVector<FixInContext, 4>>

test/Constraints/closures.swift

@@ -1163,3 +1163,13 @@ func rdar78917861() {
     }()
   }
 }
+
+// rdar://81228501 - type-checker crash due to applied invalid solution
+func test(arr: [[Int]]) {
+  struct A {
+    init(arg: [Int]) {}
+  }
+
+  arr.map { ($0 as? [Int]).map { A($0) } } // expected-error {{missing argument label 'arg:' in call}} {{36-36=arg: }}
+  // expected-warning@-1 {{conditional cast from '[Int]' to '[Int]' always succeeds}}
+}