[NFC] Move this helper for opening pack expansions into the AST

Author: rjmccall

include/swift/AST/GenericEnvironment.h

@@ -38,8 +38,10 @@ class OpaqueTypeDecl;
 class ElementArchetypeType;
 class OpenedArchetypeType;
 class PackArchetypeType;
+class PackExpansionType;
 class SILModule;
 class SILType;
+template <class> class CanTypeWrapper;
 
 /// Query function suitable for use as a \c TypeSubstitutionFn that queries
 /// the mapping of interface types to archetypes.
@@ -310,6 +312,23 @@ class alignas(1 << DeclAlignInBits) GenericEnvironment final
 
   SWIFT_DEBUG_DUMP;
 };
+
+/// A pair of an opened-element generic signature and an opened-element
+/// generic environment.
+struct OpenedElementContext {
+  /// The opened-element environment for this expansion.
+  GenericEnvironment *environment;
+
+  /// The opened-element signature for this expansion.
+  CanGenericSignature signature;
+
+  /// Create a fresh opened element context from a contextual pack
+  /// expansion type.  This is useful when writing code that needs to
+  /// break down the components of a pack expansion.
+  static OpenedElementContext
+  createForContextualExpansion(ASTContext &ctx,
+                   CanTypeWrapper<PackExpansionType> expansionType);
+};
 
 } // end namespace swift
 

lib/AST/GenericEnvironment.cpp

@@ -709,3 +709,24 @@ GenericEnvironment::mapConformanceRefIntoContext(
   auto contextType = mapTypeIntoContext(conformingInterfaceType);
   return {contextType, contextConformance};
 }
+
+OpenedElementContext
+OpenedElementContext::createForContextualExpansion(ASTContext &ctx,
+                                       CanPackExpansionType expansionType) {
+  assert(!expansionType->hasTypeParameter() &&
+         "must be given a contextual type");
+
+  // Get the outer generic signature and environment.
+  auto *genericEnv = cast<ArchetypeType>(expansionType.getCountType())
+                         ->getGenericEnvironment();
+  auto subMap = genericEnv->getForwardingSubstitutionMap();
+
+  auto genericSig = genericEnv->getGenericSignature().getCanonicalSignature();
+  // Create an opened element signature and environment.
+  auto elementSig = ctx.getOpenedElementSignature(
+      genericSig, expansionType.getCountType());
+  auto *elementEnv = GenericEnvironment::forOpenedElement(
+      elementSig, UUID::fromTime(), expansionType.getCountType(), subMap);
+
+  return {elementEnv, elementSig};
+}

lib/IRGen/GenPack.cpp

@@ -261,28 +261,6 @@ static llvm::Value *bindWitnessTableAtIndex(IRGenFunction &IGF,
   return wtable;
 }
 
-struct OpenedElementContext {
-  GenericEnvironment *environment;
-  CanGenericSignature signature;
-
-  static OpenedElementContext
-  createForPackExpansion(IRGenFunction &IGF, CanPackExpansionType expansionTy) {
-    // Get the outer generic signature and environment.
-    auto *genericEnv = cast<ArchetypeType>(expansionTy.getCountType())
-                           ->getGenericEnvironment();
-    auto subMap = genericEnv->getForwardingSubstitutionMap();
-
-    auto genericSig = genericEnv->getGenericSignature().getCanonicalSignature();
-    // Create an opened element signature and environment.
-    auto elementSig = IGF.IGM.Context.getOpenedElementSignature(
-        genericSig, expansionTy.getCountType());
-    auto *elementEnv = GenericEnvironment::forOpenedElement(
-        elementSig, UUID::fromTime(), expansionTy.getCountType(), subMap);
-
-    return {elementEnv, elementSig};
-  }
-};
-
 static void bindElementSignatureRequirementsAtIndex(
     IRGenFunction &IGF, OpenedElementContext const &context, llvm::Value *index,
     DynamicMetadataRequest request) {
@@ -417,7 +395,7 @@ static void emitPackExpansionMetadataPack(IRGenFunction &IGF, Address pack,
   emitPackExpansionPack(
       IGF, pack, expansionTy, dynamicIndex, dynamicLength, [&](auto *index) {
         auto context =
-            OpenedElementContext::createForPackExpansion(IGF, expansionTy);
+            OpenedElementContext::createForContextualExpansion(IGF.IGM.Context, expansionTy);
         auto patternTy = expansionTy.getPatternType();
         return emitPackExpansionElementMetadata(IGF, context, patternTy, index,
                                                 request);
@@ -544,7 +522,7 @@ static void emitPackExpansionWitnessTablePack(
       IGF, pack, expansionTy, dynamicIndex, dynamicLength, [&](auto *index) {
         llvm::Value *_metadata = nullptr;
         auto context =
-            OpenedElementContext::createForPackExpansion(IGF, expansionTy);
+            OpenedElementContext::createForContextualExpansion(IGF.IGM.Context, expansionTy);
         auto patternTy = expansionTy.getPatternType();
         return emitPackExpansionElementWitnessTable(
             IGF, context, patternTy, conformance,
@@ -862,7 +840,7 @@ llvm::Value *irgen::emitTypeMetadataPackElementRef(
       // pack expansion at that index.
       auto *relativeIndex = IGF.Builder.CreateSub(index, lowerBound);
       auto context =
-          OpenedElementContext::createForPackExpansion(IGF, expansionTy);
+          OpenedElementContext::createForContextualExpansion(IGF.IGM.Context, expansionTy);
       auto patternTy = expansionTy.getPatternType();
       metadata = emitPackExpansionElementMetadata(IGF, context, patternTy,
                                                   relativeIndex, request);