[CSFix] Add a fix to detect type specialization arity mismatches

The situations where number of parameters and arguments didn't match.

Author: xedin

include/swift/Sema/CSFix.h

@@ -457,6 +457,10 @@ enum class FixKind : uint8_t {
 
   /// Ignore an attempt to specialize non-generic type.
   AllowConcreteTypeSpecialization,
+
+  /// Ignore situations when provided number of generic arguments didn't match
+  /// expected number of parameters.
+  IgnoreGenericSpecializationArityMismatch,
 };
 
 class ConstraintFix {
@@ -3677,6 +3681,42 @@ class AllowConcreteTypeSpecialization final : public ConstraintFix {
   }
 };
 
+class IgnoreGenericSpecializationArityMismatch final : public ConstraintFix {
+  ValueDecl *D;
+  unsigned NumParams;
+  unsigned NumArgs;
+  bool HasParameterPack;
+
+  IgnoreGenericSpecializationArityMismatch(ConstraintSystem &cs,
+                                           ValueDecl *decl, unsigned numParams,
+                                           unsigned numArgs,
+                                           bool hasParameterPack,
+                                           ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::IgnoreGenericSpecializationArityMismatch,
+                      locator),
+        D(decl), NumParams(numParams), NumArgs(numArgs),
+        HasParameterPack(hasParameterPack) {}
+
+public:
+  std::string getName() const override {
+    return "ignore generic specialization mismatch";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
+  static IgnoreGenericSpecializationArityMismatch *
+  create(ConstraintSystem &cs, ValueDecl *decl, unsigned numParams,
+         unsigned numArgs, bool hasParameterPack, ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::IgnoreGenericSpecializationArityMismatch;
+  }
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -2842,3 +2842,19 @@ AllowConcreteTypeSpecialization::create(ConstraintSystem &cs, Type concreteTy,
   return new (cs.getAllocator())
       AllowConcreteTypeSpecialization(cs, concreteTy, locator);
 }
+
+bool IgnoreGenericSpecializationArityMismatch::diagnose(
+    const Solution &solution, bool asNote) const {
+  return false;
+}
+
+IgnoreGenericSpecializationArityMismatch *
+IgnoreGenericSpecializationArityMismatch::create(ConstraintSystem &cs,
+                                                 ValueDecl *decl,
+                                                 unsigned numParams,
+                                                 unsigned numArgs,
+                                                 bool hasParameterPack,
+                                                 ConstraintLocator *locator) {
+  return new (cs.getAllocator()) IgnoreGenericSpecializationArityMismatch(
+      cs, decl, numParams, numArgs, hasParameterPack, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -14776,7 +14776,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AllowGlobalActorMismatch:
   case FixKind::AllowAssociatedValueMismatch:
   case FixKind::GenericArgumentsMismatch:
-  case FixKind::AllowConcreteTypeSpecialization: {
+  case FixKind::AllowConcreteTypeSpecialization:
+  case FixKind::IgnoreGenericSpecializationArityMismatch: {
     return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
   }
   case FixKind::IgnoreInvalidASTNode: {