[CSFix] Add a new fix to diagnose invalid static member refs on protocol metatype

Author: xedin

include/swift/Sema/CSFix.h

@@ -307,6 +307,11 @@ enum class FixKind : uint8_t {
   /// convertible, but runtime does not support such convertions. e.g.
   /// function type casts.
   AllowUnsupportedRuntimeCheckedCast,
+
+  /// Allow reference to a static member on a protocol metatype
+  /// even though result type of the reference doesn't conform
+  /// to an expected protocol.
+  AllowInvalidStaticMemberRefOnProtocolMetatype,
 };
 
 class ConstraintFix {
@@ -2307,6 +2312,27 @@ class AllowUnsupportedRuntimeCheckedCast final
           CheckedCastKind kind, ConstraintLocator *locator);
 };
 
+class AllowInvalidStaticMemberRefOnProtocolMetatype final
+  : public ConstraintFix {
+  Type BaseType;
+
+  AllowInvalidStaticMemberRefOnProtocolMetatype(ConstraintSystem &cs,
+                                                Type baseType,
+                                                ConstraintLocator *locator)
+    : ConstraintFix(cs,
+                    FixKind::AllowInvalidStaticMemberRefOnProtocolMetatype,
+                    locator),
+      BaseType(baseType) {}
+
+  public:
+  std::string getName() const override {
+    return "allow invalid static member reference on a protocol metatype";
+  }
+
+  static AllowInvalidStaticMemberRefOnProtocolMetatype *
+  create(ConstraintSystem &cs, Type baseType, ConstraintLocator *locator);
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -1938,3 +1938,23 @@ bool AllowUnsupportedRuntimeCheckedCast::diagnose(const Solution &solution,
       solution, getFromType(), getToType(), CastKind, getLocator());
   return failure.diagnose(asNote);
 }
+
+bool AllowInvalidStaticMemberRefOnProtocolMetatype::diagnose(
+    const Solution &solution, bool asNote) const {
+  auto *locator = getLocator();
+  auto overload = solution.getOverloadChoice(locator);
+
+  auto *member = overload.choice.getDeclOrNull();
+  assert(member);
+
+  AllowTypeOrInstanceMemberFailure failure(solution, BaseType, member,
+                                           member->createNameRef(), locator);
+  return failure.diagnose(asNote);
+}
+
+AllowInvalidStaticMemberRefOnProtocolMetatype *
+AllowInvalidStaticMemberRefOnProtocolMetatype::create(
+    ConstraintSystem &cs, Type baseType, ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      AllowInvalidStaticMemberRefOnProtocolMetatype(cs, baseType, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -10525,7 +10525,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::SpecifyBaseTypeForOptionalUnresolvedMember:
   case FixKind::AllowCheckedCastCoercibleOptionalType:
   case FixKind::AllowUnsupportedRuntimeCheckedCast:
-  case FixKind::AllowAlwaysSucceedCheckedCast: {
+  case FixKind::AllowAlwaysSucceedCheckedCast:
+  case FixKind::AllowInvalidStaticMemberRefOnProtocolMetatype: {
     return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
   }