[Diagnostics] Do more checking before recording force downcast fix

lib/Sema/BuilderTransform.cpp

@@ -1564,6 +1564,13 @@ Optional<BraceStmt *> TypeChecker::applyFunctionBuilderBodyTransform(
     // The system was salvaged; continue on as if nothing happened.
   }
 
+  if (cs.isDebugMode()) {
+    auto &log = llvm::errs();
+    log << "--- Applying Solution ---\n";
+    solutions.front().dump(log);
+    log << '\n';
+  }
+
   // FIXME: Shouldn't need to do this.
   cs.applySolution(solutions.front());
 

lib/Sema/CSDiagnostics.cpp

@@ -988,8 +988,6 @@ bool MissingExplicitConversionFailure::diagnoseAsError() {
     return false;
 
   bool useAs = TypeChecker::isExplicitlyConvertibleTo(fromType, toType, DC);
-  if (!useAs && !TypeChecker::checkedCastMaySucceed(fromType, toType, DC))
-    return false;
 
   auto *expr = findParentExpr(anchor);
   if (!expr)

lib/Sema/CSSimplify.cpp

@@ -2968,6 +2968,9 @@ static bool
 repairViaBridgingCast(ConstraintSystem &cs, Type fromType, Type toType,
                       SmallVectorImpl<RestrictionOrFix> &conversionsOrFixes,
                       ConstraintLocatorBuilder locator) {
+  if (fromType->hasTypeVariable() || toType->hasTypeVariable())
+    return false;
+
   auto objectType1 = fromType->getOptionalObjectType();
   auto objectType2 = toType->getOptionalObjectType();
 
@@ -2986,6 +2989,9 @@ repairViaBridgingCast(ConstraintSystem &cs, Type fromType, Type toType,
   if (!canBridgeThroughCast(cs, fromType, toType))
     return false;
 
+  if (!TypeChecker::checkedCastMaySucceed(fromType, toType, cs.DC))
+    return false;
+
   conversionsOrFixes.push_back(ForceDowncast::create(
       cs, fromType, toType, cs.getConstraintLocator(locator)));
   return true;

test/Constraints/rdar65254452.swift

@@ -0,0 +1,17 @@
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify %s
+// REQUIRES: objc_interop
+
+import Foundation
+
+class Obj: NSObject {
+}
+
+class Container {
+  var objects: [Obj]
+  init(objects: [Obj]) {}
+}
+
+func test(other: Container) {
+  _ = Container(objects: other)
+  // expected-error@-1 {{cannot convert value of type 'Container' to expected argument type '[Obj]'}}
+}