[CSFix] Add a fix to allow value pack expansions without pack references

Situations like `repeat x` where `x` is `Int` where pack expansion
expression doesn't have any pack references.

Author: xedin

include/swift/Sema/CSFix.h

@@ -438,6 +438,9 @@ enum class FixKind : uint8_t {
   /// Allow a pack expansion parameter of N elements to be matched
   /// with a single tuple literal argument of the same arity.
   DestructureTupleToMatchPackExpansionParameter,
+
+  /// Allow value pack expansion without pack references.
+  AllowValueExpansionWithoutPackReferences,
 };
 
 class ConstraintFix {
@@ -3453,6 +3456,31 @@ class DestructureTupleToMatchPackExpansionParameter final
   }
 };
 
+class AllowValueExpansionWithoutPackReferences final : public ConstraintFix {
+  AllowValueExpansionWithoutPackReferences(ConstraintSystem &cs,
+                                           ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::AllowValueExpansionWithoutPackReferences,
+                      locator) {}
+
+public:
+  std::string getName() const override {
+    return "allow value pack expansion without pack references";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
+  static AllowValueExpansionWithoutPackReferences *
+  create(ConstraintSystem &cs, ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::AllowValueExpansionWithoutPackReferences;
+  }
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -2756,3 +2756,15 @@ DestructureTupleToMatchPackExpansionParameter::create(
   return new (cs.getAllocator())
       DestructureTupleToMatchPackExpansionParameter(cs, paramShapeTy, locator);
 }
+
+bool AllowValueExpansionWithoutPackReferences::diagnose(
+    const Solution &solution, bool asNote) const {
+  return false;
+}
+
+AllowValueExpansionWithoutPackReferences *
+AllowValueExpansionWithoutPackReferences::create(ConstraintSystem &cs,
+                                                 ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      AllowValueExpansionWithoutPackReferences(cs, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -14814,6 +14814,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AllowTupleLabelMismatch:
   case FixKind::AddExplicitExistentialCoercion:
   case FixKind::DestructureTupleToMatchPackExpansionParameter:
+  case FixKind::AllowValueExpansionWithoutPackReferences:
     llvm_unreachable("handled elsewhere");
   }