[CSFix] Add a skeleton of a fix for missing each in value pack reference

Author: xedin

include/swift/Sema/CSFix.h

@@ -444,6 +444,9 @@ enum class FixKind : uint8_t {
 
   /// Allow value pack expansion without pack references.
   AllowValueExpansionWithoutPackReferences,
+
+  /// Ignore missing 'each' keyword before value pack reference.
+  IgnoreMissingEachKeyword,
 };
 
 class ConstraintFix {
@@ -3506,6 +3509,33 @@ class AllowValueExpansionWithoutPackReferences final : public ConstraintFix {
   }
 };
 
+class IgnoreMissingEachKeyword final : public ConstraintFix {
+  Type ValuePackType;
+
+  IgnoreMissingEachKeyword(ConstraintSystem &cs, Type valuePackTy,
+                           ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::IgnoreMissingEachKeyword, locator),
+        ValuePackType(valuePackTy) {}
+
+public:
+  std::string getName() const override {
+    return "allow value pack reference without 'each'";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
+  static IgnoreMissingEachKeyword *
+  create(ConstraintSystem &cs, Type valuePackTy, ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::IgnoreMissingEachKeyword;
+  }
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -2784,3 +2784,15 @@ AllowValueExpansionWithoutPackReferences::create(ConstraintSystem &cs,
   return new (cs.getAllocator())
       AllowValueExpansionWithoutPackReferences(cs, locator);
 }
+
+bool IgnoreMissingEachKeyword::diagnose(const Solution &solution,
+                                        bool asNote) const {
+  return false;
+}
+
+IgnoreMissingEachKeyword *
+IgnoreMissingEachKeyword::create(ConstraintSystem &cs, Type valuePackTy,
+                                 ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      IgnoreMissingEachKeyword(cs, valuePackTy, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -14771,6 +14771,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AddExplicitExistentialCoercion:
   case FixKind::DestructureTupleToMatchPackExpansionParameter:
   case FixKind::AllowValueExpansionWithoutPackReferences:
+  case FixKind::IgnoreMissingEachKeyword:
     llvm_unreachable("handled elsewhere");
   }