Revert "Sema: Allow optional-to-optional CGFloat <-> Double conversion"

This reverts commit f0f5ffc.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -7489,18 +7489,28 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
         // Look through all value-to-optional promotions to allow
         // conversions like Double -> CGFloat?? and vice versa.
         // T -> Optional<T>
-        if (location.endsWith<LocatorPathElt::OptionalInjection>() ||
-            location.endsWith<LocatorPathElt::GenericArgument>()) {
+        if (location.endsWith<LocatorPathElt::OptionalInjection>()) {
           SmallVector<LocatorPathElt, 4> path;
           auto anchor = location.getLocatorParts(path);
 
-          // Drop all of the applied `value-to-optional` and
-          // `optional-to-optional` conversions.
+          // An attempt at Double/CGFloat conversion through
+          // optional chaining. This is not supported at the
+          // moment because solution application doesn't know
+          // how to map Double to/from CGFloat through optionals.
+          if (isExpr<OptionalEvaluationExpr>(anchor)) {
+            if (!shouldAttemptFixes())
+              return getTypeMatchFailure(locator);
+
+            conversionsOrFixes.push_back(ContextualMismatch::create(
+                *this, nominal1, nominal2, getConstraintLocator(locator)));
+            break;
+          }
+
+          // Drop all of the applied `value-to-optional` promotions.
           path.erase(llvm::remove_if(
                          path,
                          [](const LocatorPathElt &elt) {
-                           return elt.is<LocatorPathElt::OptionalInjection>() ||
-                                  elt.is<LocatorPathElt::GenericArgument>();
+                           return elt.is<LocatorPathElt::OptionalInjection>();
                          }),
                      path.end());
 

test/Constraints/implicit_double_cgfloat_conversion.swift

@@ -349,8 +349,3 @@ func test_init_validation() {
     }
   }
 }
-
-// Optional-to-optional conversion
-func optional_to_optional(x: CGFloat?) -> Double? {
-  return x
-}

validation-test/Sema/type_checker_crashers_fixed/rdar83666783.swift

@@ -12,5 +12,5 @@ func compute(_: Double?) -> Double? {
 }
 
 func test(s: S?) {
-  _ = compute(s?.test)
+  _ = compute(s?.test) // expected-error {{cannot implicitly convert value of type 'CGFloat?' to expected type 'Double?'}}
 }