[Diagnostics] Don't record unwrap fix if ? was used incorrectly

In situations like `""?` or `42?`, let's not record an unwrap fix
since it was incorrect to use `?` in the first place.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -3243,7 +3243,14 @@ repairViaOptionalUnwrap(ConstraintSystem &cs, Type fromType, Type toType,
   // behind itself which we can use to better understand
   // how many levels of optionality have to be unwrapped.
   if (auto *OEE = dyn_cast<OptionalEvaluationExpr>(anchor)) {
-    auto type = cs.getType(OEE->getSubExpr());
+    auto *subExpr = OEE->getSubExpr();
+
+    // First, let's check whether it has been determined that
+    // it was incorrect to use `?` in this position.
+    if (cs.hasFixFor(cs.getConstraintLocator(subExpr), FixKind::RemoveUnwrap))
+      return true;
+
+    auto type = cs.getType(subExpr);
     // If the type of sub-expression is optional, type of the
     // `OptionalEvaluationExpr` could be safely ignored because
     // it doesn't add any type information.

test/Constraints/optional.swift

@@ -425,8 +425,9 @@ func test_force_unwrap_not_being_too_eager() {
 
 // rdar://problem/57097401
 func invalidOptionalChaining(a: Any) {
-  a == "="? // expected-error {{binary operator '==' cannot be applied to operands of type 'Any' and 'String?'}}
-  // expected-note@-1 {{overloads for '==' exist with these partially matching parameter lists: (CodingUserInfoKey, CodingUserInfoKey), (FloatingPointSign, FloatingPointSign), (String, String), (Unicode.CanonicalCombiningClass, Unicode.CanonicalCombiningClass)}}
+  a == "="? // expected-error {{cannot use optional chaining on non-optional value of type 'String'}}
+  // expected-error@-1 {{protocol 'Any' as a type cannot conform to 'Equatable'}}
+  // expected-note@-2 {{requirement from conditional conformance of 'Any?' to 'Equatable'}} expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
 }
 
 // SR-12309 - Force unwrapping 'nil' compiles without warning