[CSFix] Add a fix to detect invalid specialization of non-generic types

Author: xedin

include/swift/Sema/CSFix.h

@@ -454,6 +454,9 @@ enum class FixKind : uint8_t {
   /// Ignore the fact that member couldn't be referenced within init accessor
   /// because its name doesn't appear in 'initializes' or 'accesses' attributes.
   AllowInvalidMemberReferenceInInitAccessor,
+
+  /// Ignore an attempt to specialize non-generic type.
+  AllowConcreteTypeSpecialization,
 };
 
 class ConstraintFix {
@@ -3647,6 +3650,33 @@ class AllowInvalidMemberReferenceInInitAccessor final : public ConstraintFix {
   }
 };
 
+class AllowConcreteTypeSpecialization final : public ConstraintFix {
+  Type ConcreteType;
+
+  AllowConcreteTypeSpecialization(ConstraintSystem &cs, Type concreteTy,
+                                  ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::AllowConcreteTypeSpecialization, locator),
+        ConcreteType(concreteTy) {}
+
+public:
+  std::string getName() const override {
+    return "allow concrete type specialization";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
+  static AllowConcreteTypeSpecialization *
+  create(ConstraintSystem &cs, Type concreteTy, ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::AllowConcreteTypeSpecialization;
+  }
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -2829,3 +2829,15 @@ AllowInvalidMemberReferenceInInitAccessor::create(ConstraintSystem &cs,
   return new (cs.getAllocator())
       AllowInvalidMemberReferenceInInitAccessor(cs, memberName, locator);
 }
+
+bool AllowConcreteTypeSpecialization::diagnose(const Solution &solution,
+                                               bool asNote) const {
+  return false;
+}
+
+AllowConcreteTypeSpecialization *
+AllowConcreteTypeSpecialization::create(ConstraintSystem &cs, Type concreteTy,
+                                        ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      AllowConcreteTypeSpecialization(cs, concreteTy, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -13657,6 +13657,10 @@ ConstraintSystem::simplifyExplicitGenericArgumentsConstraint(
       }
     }
   }
+
+  if (openedGenericParams.empty())
+    return SolutionKind::Error;
+
   assert(openedGenericParams.size() == genericParams->size());
 
   // Match the opened generic parameters to the specialized arguments.
@@ -14764,7 +14768,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::MacroMissingPound:
   case FixKind::AllowGlobalActorMismatch:
   case FixKind::AllowAssociatedValueMismatch:
-  case FixKind::GenericArgumentsMismatch: {
+  case FixKind::GenericArgumentsMismatch:
+  case FixKind::AllowConcreteTypeSpecialization: {
     return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
   }
   case FixKind::IgnoreInvalidASTNode: {