[CSFix] Add a specific kind for AllowInOutConversion

Author: xedin

include/swift/Sema/CSFix.h

@@ -357,6 +357,10 @@ enum class FixKind : uint8_t {
 
   /// Ignore a type imposed by an assignment destination e.g. `let x: Int = ...`
   IgnoreAssignmentDestinationType,
+
+  /// Allow argument-to-parameter subtyping even when parameter type
+  /// is marked as `inout`.
+  AllowConversionThroughInOut,
 };
 
 class ConstraintFix {
@@ -1993,7 +1997,8 @@ class IgnoreAssignmentDestinationType final : public ContextualMismatch {
 class AllowInOutConversion final : public ContextualMismatch {
   AllowInOutConversion(ConstraintSystem &cs, Type argType, Type paramType,
                        ConstraintLocator *locator)
-      : ContextualMismatch(cs, argType, paramType, locator) {}
+      : ContextualMismatch(cs, FixKind::AllowConversionThroughInOut, argType,
+                           paramType, locator) {}
 
 public:
   std::string getName() const override {
@@ -2005,6 +2010,10 @@ class AllowInOutConversion final : public ContextualMismatch {
   static AllowInOutConversion *create(ConstraintSystem &cs, Type argType,
                                       Type paramType,
                                       ConstraintLocator *locator);
+
+  static bool classof(ConstraintFix *fix) {
+    return fix->getKind() == FixKind::AllowConversionThroughInOut;
+  }
 };
 
 class AllowArgumentMismatch : public ContextualMismatch {

lib/Sema/CSSimplify.cpp

@@ -11687,7 +11687,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
 
   case FixKind::ContextualMismatch:
   case FixKind::IgnoreContextualType:
-  case FixKind::IgnoreAssignmentDestinationType: {
+  case FixKind::IgnoreAssignmentDestinationType:
+  case FixKind::AllowConversionThroughInOut: {
     auto impact = 1;
 
     auto locator = fix->getLocator();