[CSFix] Add a fix to detect incorrect argument to subscript key path index

Author: xedin

include/swift/Sema/CSFix.h

@@ -463,6 +463,10 @@ enum class FixKind : uint8_t {
   /// Ignore situations when provided number of generic arguments didn't match
   /// expected number of parameters.
   IgnoreGenericSpecializationArityMismatch,
+
+  /// Ignore situations when key path subscript index gets passed an invalid
+  /// type as an argument (something that is not a key path).
+  IgnoreKeyPathSubscriptIndexMismatch,
 };
 
 class ConstraintFix {
@@ -3742,6 +3746,30 @@ class IgnoreGenericSpecializationArityMismatch final : public ConstraintFix {
   }
 };
 
+class IgnoreKeyPathSubscriptIndexMismatch final : public ConstraintFix {
+  Type ArgType;
+
+  IgnoreKeyPathSubscriptIndexMismatch(ConstraintSystem &cs, Type argTy,
+                                      ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::IgnoreKeyPathSubscriptIndexMismatch,
+                      locator),
+        ArgType(argTy) {}
+
+public:
+  std::string getName() const override {
+    return "ignore invalid key path subscript index";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  static IgnoreKeyPathSubscriptIndexMismatch *
+  create(ConstraintSystem &cs, Type argType, ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::IgnoreKeyPathSubscriptIndexMismatch;
+  }
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -2880,3 +2880,16 @@ IgnoreGenericSpecializationArityMismatch::create(ConstraintSystem &cs,
   return new (cs.getAllocator()) IgnoreGenericSpecializationArityMismatch(
       cs, decl, numParams, numArgs, hasParameterPack, locator);
 }
+
+bool IgnoreKeyPathSubscriptIndexMismatch::diagnose(const Solution &solution,
+                                                   bool asNote) const {
+  InvalidTypeAsKeyPathSubscriptIndex failure(solution, ArgType, getLocator());
+  return failure.diagnose(asNote);
+}
+
+IgnoreKeyPathSubscriptIndexMismatch *
+IgnoreKeyPathSubscriptIndexMismatch::create(ConstraintSystem &cs, Type argType,
+                                            ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      IgnoreKeyPathSubscriptIndexMismatch(cs, argType, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -12417,7 +12417,7 @@ ConstraintSystem::simplifyKeyPathApplicationConstraint(
   }
   if (!keyPathTy->isTypeVariableOrMember())
     return SolutionKind::Error;
-  
+
   return unsolved();
 }
 
@@ -14900,7 +14900,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AllowAssociatedValueMismatch:
   case FixKind::GenericArgumentsMismatch:
   case FixKind::AllowConcreteTypeSpecialization:
-  case FixKind::IgnoreGenericSpecializationArityMismatch: {
+  case FixKind::IgnoreGenericSpecializationArityMismatch:
+  case FixKind::IgnoreKeyPathSubscriptIndexMismatch: {
     return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
   }
   case FixKind::IgnoreThrownErrorMismatch: {