[ConstraintSystem] remove TupleType::isSingleUnlabeledPackExpansion in favor of constraints::getPatternTypeOfSingleUnlabeledPackExpansionTuple

include/swift/AST/Types.h

@@ -2494,10 +2494,6 @@ class TupleType final : public TypeBase, public llvm::FoldingSetNode,
 
   bool containsPackExpansionType() const;
 
-  /// Check whether this tuple consists of a single unlabeled element
-  /// of \c PackExpansionType.
-  bool isSingleUnlabeledPackExpansion() const;
-
 private:
   TupleType(ArrayRef<TupleTypeElt> elements, const ASTContext *CanCtx,
             RecursiveTypeProperties properties)

include/swift/Sema/ConstraintSystem.h

@@ -6268,6 +6268,9 @@ Type isPlaceholderVar(PatternBindingDecl *PB);
 /// Dump an anchor node for a constraint locator or contextual type.
 void dumpAnchor(ASTNode anchor, SourceManager *SM, raw_ostream &out);
 
+/// Check whether the type is a tuple consisting of a single unlabeled element
+/// of \c PackExpansionType or a type variable that represents a pack expansion
+/// type.
 bool isSingleUnlabeledPackExpansionTuple(Type type);
 
 /// \returns null if \c type is not a single unlabeled pack expansion tuple.

lib/AST/ParameterPack.cpp

@@ -276,14 +276,6 @@ bool CanTupleType::containsPackExpansionTypeImpl(CanTupleType tuple) {
   return false;
 }
 
-bool TupleType::isSingleUnlabeledPackExpansion() const {
-  if (getNumElements() != 1)
-    return false;
-
-  const auto &elt = getElement(0);
-  return !elt.hasName() && elt.getType()->is<PackExpansionType>();
-}
-
 bool AnyFunctionType::containsPackExpansionType(ArrayRef<Param> params) {
   for (auto param : params) {
     auto paramTy = param.getPlainType();

lib/Sema/CSApply.cpp

@@ -3858,10 +3858,9 @@ namespace {
       if (auto *packRefExpr = expr->getPackRefExpr()) {
         packRefExpr = cs.coerceToRValue(packRefExpr);
         auto packRefType = cs.getType(packRefExpr);
-        if (auto *tuple = packRefType->getRValueType()->getAs<TupleType>();
-            tuple && tuple->isSingleUnlabeledPackExpansion()) {
-          auto patternType =
-              getPatternTypeOfSingleUnlabeledPackExpansionTuple(tuple);
+        if (auto patternType =
+                getPatternTypeOfSingleUnlabeledPackExpansionTuple(
+                    packRefType)) {
           auto *materializedPackExpr = MaterializePackExpr::create(
               cs.getASTContext(), packRefExpr, packRefExpr->getLoc(),
               patternType, /*implicit*/ true);

lib/Sema/CSSimplify.cpp

@@ -135,12 +135,21 @@ bool constraints::isSingleUnlabeledPackExpansionTuple(Type type) {
 }
 
 Type constraints::getPatternTypeOfSingleUnlabeledPackExpansionTuple(Type type) {
-  if (!isSingleUnlabeledPackExpansionTuple(type)) {
-    return {};
+  if (isSingleUnlabeledPackExpansionTuple(type)) {
+    auto tuple = type->getRValueType()->castTo<TupleType>();
+    const auto &tupleElement = tuple->getElementType(0);
+    if (auto *expansion = tupleElement->getAs<PackExpansionType>()) {
+      return expansion->getPatternType();
+    }
+    if (auto *typeVar = tupleElement->getAs<TypeVariableType>()) {
+      auto *locator = typeVar->getImpl().getLocator();
+      if (auto expansionElement =
+              locator->getLastElementAs<LocatorPathElt::PackExpansionType>()) {
+        return expansionElement->getOpenedType()->getPatternType();
+      }
+    }
   }
-  auto tuple = type->getRValueType()->castTo<TupleType>();
-  auto *expansion = tuple->getElementType(0)->castTo<PackExpansionType>();
-  return expansion->getPatternType();
+  return {};
 }
 
 static bool containsPackExpansionType(ArrayRef<AnyFunctionType::Param> params) {

lib/Sema/TypeCheckStmt.cpp

@@ -14,19 +14,18 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "TypeChecker.h"
+#include "MiscDiagnostics.h"
 #include "TypeCheckAvailability.h"
 #include "TypeCheckConcurrency.h"
 #include "TypeCheckDistributed.h"
 #include "TypeCheckType.h"
-#include "MiscDiagnostics.h"
-#include "swift/Subsystems.h"
+#include "TypeChecker.h"
 #include "swift/AST/ASTPrinter.h"
 #include "swift/AST/ASTScope.h"
-#include "swift/AST/ASTWalker.h"
 #include "swift/AST/ASTVisitor.h"
-#include "swift/AST/DiagnosticsSema.h"
+#include "swift/AST/ASTWalker.h"
 #include "swift/AST/DiagnosticSuppression.h"
+#include "swift/AST/DiagnosticsSema.h"
 #include "swift/AST/Identifier.h"
 #include "swift/AST/Initializer.h"
 #include "swift/AST/NameLookup.h"
@@ -41,7 +40,9 @@
 #include "swift/Basic/TopCollection.h"
 #include "swift/Parse/Lexer.h"
 #include "swift/Parse/Parser.h"
+#include "swift/Sema/ConstraintSystem.h"
 #include "swift/Sema/IDETypeChecking.h"
+#include "swift/Subsystems.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/SmallString.h"
@@ -1751,7 +1752,7 @@ Stmt *PreCheckReturnStmtRequest::evaluate(Evaluator &evaluator, ReturnStmt *RS,
 static bool isDiscardableType(Type type) {
   // If type is `(_: repeat ...)`, it can be discardable.
   if (auto *tuple = type->getAs<TupleType>()) {
-    if (tuple->isSingleUnlabeledPackExpansion()) {
+    if (constraints::isSingleUnlabeledPackExpansionTuple(tuple)) {
       type = tuple->getElementType(0);
     }
   }