[Diagnostics] Don't attempt to force unwrap invalid optional chaining in the argument position

If the argument has an extra `?` or `!`, let's not attempt to force
optional (because it's use is already invalid) and re-introduce
the constraint with unwrapped type instead. This would help to diagnose
the invalid chaining as well as any argument to parameter mismatches.

Resolves: rdar://126080504

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -5883,6 +5883,24 @@ bool ConstraintSystem::repairFailures(
       if (hasConversionOrRestriction(ConversionRestrictionKind::Existential))
         break;
 
+      if (auto *typeVar =
+              lhs->getOptionalObjectType()->getAs<TypeVariableType>()) {
+        auto *argLoc = typeVar->getImpl().getLocator();
+        if (argLoc->directlyAt<OptionalEvaluationExpr>()) {
+          auto OEE = castToExpr<OptionalEvaluationExpr>(argLoc->getAnchor());
+          // If the optional chain in the argument position is invalid
+          // let's unwrap optional and re-introduce the constraint to
+          // be solved later once both sides are sufficiently resolved,
+          // this would allow to diagnose not only the invalid unwrap
+          // but an invalid conversion (if any) as well.
+          if (hasFixFor(getConstraintLocator(OEE->getSubExpr()),
+                        FixKind::RemoveUnwrap)) {
+            addConstraint(matchKind, typeVar, rhs, loc);
+            return true;
+          }
+        }
+      }
+
       auto result = matchTypes(lhs->getOptionalObjectType(), rhs, matchKind,
                                TMF_ApplyingFix, locator);
 

test/Constraints/optional.swift

@@ -435,7 +435,7 @@ func test_force_unwrap_not_being_too_eager() {
 // rdar://problem/57097401
 func invalidOptionalChaining(a: Any) {
   a == "="? // expected-error {{cannot use optional chaining on non-optional value of type 'String'}}
-  // expected-error@-1 {{binary operator '==' cannot be applied to operands of type 'Any' and 'String?'}}
+  // expected-error@-1 {{cannot convert value of type 'Any' to expected argument type 'String'}}
 }
 
 /// https://github.com/apple/swift/issues/54739
@@ -595,3 +595,15 @@ do {
   test(x!) // expected-error {{no exact matches in call to local function 'test'}}
   // expected-error@-1 {{cannot force unwrap value of non-optional type 'Double'}}
 }
+
+func testExtraQuestionMark(action: () -> Void, v: Int) {
+  struct Test {
+    init(action: () -> Void) {}
+  }
+
+  Test(action: action?)
+  // expected-error@-1 {{cannot use optional chaining on non-optional value of type '() -> Void'}}
+  Test(action: v?)
+  // expected-error@-1 {{cannot convert value of type 'Int' to expected argument type '() -> Void'}}
+  // expected-error@-2 {{cannot use optional chaining on non-optional value of type 'Int'}}
+}