AST: Use TypeTransform::transformSubMap() to transform SILBoxType

Author: slavapestov

include/swift/AST/TypeTransform.h

@@ -164,32 +164,30 @@ case TypeKind::Id:
     case TypeKind::SILBox: {
       bool changed = false;
       auto boxTy = cast<SILBoxType>(base);
-  #ifndef NDEBUG
-      // This interface isn't suitable for updating the substitution map in a
-      // generic SILBox.
-      for (Type type : boxTy->getSubstitutions().getReplacementTypes()) {
-        assert(type->isEqual(
-                   doIt(type, TypePosition::Invariant)) &&
-               "SILBoxType substitutions can't be transformed");
-      }
-  #endif
+
       SmallVector<SILField, 4> newFields;
       auto *l = boxTy->getLayout();
       for (auto f : l->getFields()) {
         auto fieldTy = f.getLoweredType();
-        auto transformed = doIt(fieldTy, TypePosition::Invariant)
-                ->getCanonicalType();
+        auto transformed = asDerived().transformSILField(
+          fieldTy, TypePosition::Invariant);
         changed |= fieldTy != transformed;
         newFields.push_back(SILField(transformed, f.isMutable()));
       }
+
+      auto oldSubMap = boxTy->getSubstitutions();
+      auto newSubMap = asDerived().transformSubMap(oldSubMap);
+      if (oldSubMap && !newSubMap)
+        return Type();
+      changed |= (oldSubMap != newSubMap);
       if (!changed)
         return t;
       boxTy = SILBoxType::get(ctx,
                               SILLayout::get(ctx,
                                              l->getGenericSignature(),
                                              newFields,
                                              l->capturesGenericEnvironment()),
-                              boxTy->getSubstitutions());
+                              newSubMap);
       return boxTy;
     }
 
@@ -1013,6 +1011,10 @@ case TypeKind::Id:
         QueryReplacementTypeArray{sig, newSubs},
         LookUpConformanceInModule());
   }
+
+  CanType transformSILField(CanType fieldTy, TypePosition pos) {
+    return doIt(fieldTy, pos)->getCanonicalType();
+  }
 };
 
 }

lib/AST/TypeSubstitution.cpp

@@ -491,6 +491,8 @@ class TypeSubstituter : public TypeTransform<TypeSubstituter> {
   std::optional<Type> transform(TypeBase *type, TypePosition position);
 
   SubstitutionMap transformSubstitutionMap(SubstitutionMap subs);
+
+  CanType transformSILField(CanType fieldTy, TypePosition pos);
 };
 
 }
@@ -504,17 +506,6 @@ TypeSubstituter::transform(TypeBase *type, TypePosition position) {
          "should not be doing AST type-substitution on a lowered SIL type;"
          "use SILType::subst");
 
-  // Special-case handle SILBoxTypes and substituted SILFunctionTypes;
-  // we want to structurally substitute the substitutions.
-  if (auto boxTy = dyn_cast<SILBoxType>(type)) {
-    auto subMap = boxTy->getSubstitutions();
-    auto newSubMap = subMap.subst(IFS);
-
-    return SILBoxType::get(boxTy->getASTContext(),
-                           boxTy->getLayout(),
-                           newSubMap);
-  }
-
   if (auto packExpansionTy = dyn_cast<PackExpansionType>(type)) {
     auto eltTys = IFS.expandPackExpansionType(packExpansionTy);
     if (eltTys.size() == 1)
@@ -617,6 +608,13 @@ SubstitutionMap TypeSubstituter::transformSubstitutionMap(SubstitutionMap subs)
   return subs.subst(IFS);
 }
 
+CanType TypeSubstituter::transformSILField(CanType fieldTy, TypePosition pos) {
+  // Type substitution does not walk into the SILBoxType's field types, because
+  // that's written with respect to the generic signature of the box type,
+  // and not the input generic signature of the substitution.
+  return fieldTy;
+}
+
 Type Type::subst(SubstitutionMap substitutions,
                  SubstOptions options) const {
   InFlightSubstitutionViaSubMap IFS(substitutions, options);

lib/IRGen/IRGenDebugInfo.cpp

@@ -103,6 +103,8 @@ class EqualUpToClangTypes
   };
 };
 
+/// FIXME: This should be removed in favor of fixing ASTDemangler to wrap types in
+/// ExistentialType where appropriate.
 static bool equalWithoutExistentialTypes(Type t1, Type t2) {
   static Type (*withoutExistentialTypes)(Type) = [](Type type) -> Type {
     return type.transformRec([](TypeBase *type) -> std::optional<Type> {

test/DebugInfo/sil-box-subst-func-type.swift

@@ -0,0 +1,9 @@
+// RUN: %target-swift-frontend -emit-ir -g %s | %FileCheck %s
+
+func f<T>(_ g: @escaping (() -> T) -> T) -> (() -> T) {
+    var h: (() -> T)? = nil
+    h = { () -> T in g(h!) }
+    return h!
+}
+
+// CHECK-LABEL: !DICompositeType(tag: DW_TAG_structure_type, name: "$sxIegr_Sgz_x_lXXD",