Generalize the Mangling of Constrained Existential Types

Upgrade the old mangling from a list of argument types to a
list of requiremnets. For now, only same-type requirements
may actually be mangled since those are all that are available
to the surface language.

Reconstruction of existential types now consists of demangling (a list of)
base protocol(s), decoding the constraints, and converting the same-type
constraints back into a list of arguments.

rdar://96088707

Author: CodaFi

docs/ABI/Mangling.rst

@@ -638,7 +638,7 @@ Types
   type ::= protocol-list 'p'                 // existential type
   type ::= protocol-list superclass 'Xc'     // existential type with superclass
   type ::= protocol-list 'Xl'                // existential type with AnyObject
-  type ::= protocol-list 'y' (type* '_')* type* retroactive-conformance* 'XP'   // parameterized protocol type
+  type ::= protocol-list requirement* '_' 'XP'   // constrained existential type
   type ::= type-list 't'                     // tuple
   type ::= type generic-signature 'u'        // generic type
   type ::= 'x'                               // generic param, depth=0, idx=0
@@ -879,6 +879,7 @@ now codified into the ABI; the index 0 is therefore reserved.
   GENERIC-PARAM-INDEX ::= 'z'                // depth = 0,   idx = 0
   GENERIC-PARAM-INDEX ::= INDEX              // depth = 0,   idx = N+1
   GENERIC-PARAM-INDEX ::= 'd' INDEX INDEX    // depth = M+1, idx = N
+  GENERIC-PARAM-INDEX ::= 's'                // depth = 0,   idx = 0; Constrained existential 'Self' type
 
   LAYOUT-CONSTRAINT ::= 'N'  // NativeRefCountedObject
   LAYOUT-CONSTRAINT ::= 'R'  // RefCountedObject

include/swift/AST/ASTDemangler.h

@@ -119,7 +119,8 @@ class ASTBuilder {
 
   Type createProtocolTypeFromDecl(ProtocolDecl *protocol);
 
-  Type createParameterizedProtocolType(Type base, ArrayRef<Type> args);
+  Type createConstrainedExistentialType(Type base,
+                                        ArrayRef<BuiltRequirement> constraints);
 
   Type createExistentialMetatypeType(Type instance,
                      Optional<Demangle::ImplMetatypeRepresentation> repr=None);

include/swift/AST/ASTMangler.h

@@ -343,7 +343,8 @@ class ASTMangler : public Mangler {
                                         bool &isAssocTypeAtDepth);
 
   void appendOpWithGenericParamIndex(StringRef,
-                                     const GenericTypeParamType *paramTy);
+                                     const GenericTypeParamType *paramTy,
+                                     bool baseIsProtocolSelf = false);
 
   /// Mangles a sugared type iff we are mangling for the debugger.
   template <class T> void appendSugaredType(Type type,
@@ -444,8 +445,17 @@ class ASTMangler : public Mangler {
   bool appendGenericSignature(GenericSignature sig,
                               GenericSignature contextSig = nullptr);
 
-  void appendRequirement(const Requirement &reqt,
-                         GenericSignature sig);
+  /// Append a requirement to the mangling.
+  ///
+  /// \param reqt The requirement to mangle
+  /// \param sig  The generic signature.
+  /// \param lhsBaseIsProtocolSelf If \c true, mangle the base of the left-hand
+  /// side of the constraint with a special protocol 'Self' sentinel node. This
+  /// supports distinguishing requirements rooted at 'Self' in constrained
+  /// existentials from ambient generic parameters that would otherwise be
+  /// at e.g. (0, 0) as well.
+  void appendRequirement(const Requirement &reqt, GenericSignature sig,
+                         bool lhsBaseIsProtocolSelf = false);
 
   void appendGenericSignatureParts(GenericSignature sig,
                                    ArrayRef<CanTypeWrapper<GenericTypeParamType>> params,
@@ -521,6 +531,9 @@ class ASTMangler : public Mangler {
                                    Demangle::AutoDiffFunctionKind kind,
                                    const AutoDiffConfig &config);
   void appendIndexSubset(IndexSubset *indexSubset);
+
+  void appendConstrainedExistential(Type base, GenericSignature sig,
+                                    const ValueDecl *forDecl);
 };
 
 } // end namespace Mangle

include/swift/Demangling/DemangleNodes.def

@@ -98,6 +98,9 @@ NODE(FunctionSignatureSpecializationReturn)
 NODE(FunctionSignatureSpecializationParamKind)
 NODE(FunctionSignatureSpecializationParamPayload)
 NODE(FunctionType)
+NODE(ConstrainedExistential)
+NODE(ConstrainedExistentialRequirementList)
+NODE(ConstrainedExistentialSelf)
 NODE(GenericPartialSpecialization)
 NODE(GenericPartialSpecializationNotReAbstracted)
 NODE(GenericProtocolWitnessTable)
@@ -170,7 +173,6 @@ NODE(EscapingObjCBlock)
 CONTEXT_NODE(OtherNominalType)
 CONTEXT_NODE(OwningAddressor)
 CONTEXT_NODE(OwningMutableAddressor)
-NODE(ParameterizedProtocol)
 NODE(PartialApplyForwarder)
 NODE(PartialApplyObjCForwarder)
 NODE(PostfixOperator)

include/swift/Demangling/Demangler.h

@@ -584,6 +584,8 @@ class Demangler : public NodeFactory {
   NodePointer demangleIndexSubset();
   NodePointer demangleDifferentiableFunctionType();
 
+  NodePointer demangleConstrainedExistentialRequirementList();
+
   bool demangleBoundGenerics(Vector<NodePointer> &TypeListList,
                              NodePointer &RetroactiveConformances);
 

include/swift/Demangling/TypeDecoder.h

@@ -713,7 +713,7 @@ class TypeDecoder {
                                                    forRequirement);
     }
 
-    case NodeKind::ParameterizedProtocol: {
+    case NodeKind::ConstrainedExistential: {
       if (Node->getNumChildren() < 2)
         return MAKE_NODE_TYPE_ERROR(Node,
                                     "fewer children (%zu) than required (2)",
@@ -723,23 +723,20 @@ class TypeDecoder {
       if (protocolType.isError())
         return protocolType;
 
-      llvm::SmallVector<BuiltType, 8> args;
+      llvm::SmallVector<BuiltRequirement, 8> requirements;
 
-      const auto &genericArgs = Node->getChild(1);
-      if (genericArgs->getKind() != NodeKind::TypeList)
-        return MAKE_NODE_TYPE_ERROR0(genericArgs, "is not TypeList");
+      auto *reqts = Node->getChild(1);
+      if (reqts->getKind() != NodeKind::ConstrainedExistentialRequirementList)
+        return MAKE_NODE_TYPE_ERROR0(reqts, "is not requirement list");
 
-      for (auto genericArg : *genericArgs) {
-        auto paramType = decodeMangledType(genericArg, depth + 1,
-                                           /*forRequirement=*/false);
-        if (paramType.isError())
-          return paramType;
-        args.push_back(paramType.getType());
-      }
+      decodeRequirement<BuiltType, BuiltRequirement, BuiltLayoutConstraint,
+                        BuilderType>(reqts, requirements, Builder);
 
-      return Builder.createParameterizedProtocolType(protocolType.getType(),
-                                                     args);
+      return Builder.createConstrainedExistentialType(protocolType.getType(),
+                                                      requirements);
     }
+    case NodeKind::ConstrainedExistentialSelf:
+      return Builder.createGenericTypeParameterType(/*depth*/ 0, /*index*/ 0);
 
     case NodeKind::Protocol:
     case NodeKind::ProtocolSymbolicReference: {

include/swift/Reflection/TypeRef.h

@@ -563,39 +563,48 @@ class ProtocolCompositionTypeRef final : public TypeRef {
   }
 };
 
-class ParameterizedProtocolTypeRef final : public TypeRef {
+class ConstrainedExistentialTypeRef final : public TypeRef {
   const ProtocolCompositionTypeRef *Base;
-  std::vector<const TypeRef *> Args;
+  std::vector<TypeRefRequirement> Requirements;
 
   static TypeRefID Profile(const ProtocolCompositionTypeRef *Protocol,
-                           std::vector<const TypeRef *> Args) {
+                           std::vector<TypeRefRequirement> Requirements) {
     TypeRefID ID;
     ID.addPointer(Protocol);
-    for (auto Arg : Args) {
-      ID.addPointer(Arg);
+    for (auto reqt : Requirements) {
+      ID.addPointer(reqt.getFirstType());
+      if (reqt.getKind() != RequirementKind::Layout)
+        ID.addPointer(reqt.getSecondType());
+      else
+        ID.addInteger(
+            unsigned(0)); // FIXME: Layout constraints aren't implemented yet
+      ID.addInteger(unsigned(reqt.getKind()));
     }
     return ID;
   }
 
 public:
-  ParameterizedProtocolTypeRef(const ProtocolCompositionTypeRef *Protocol,
-                               std::vector<const TypeRef *> Args)
-      : TypeRef(TypeRefKind::ParameterizedProtocol), Base(Protocol),
-        Args(Args) {}
+  ConstrainedExistentialTypeRef(const ProtocolCompositionTypeRef *Protocol,
+                                std::vector<TypeRefRequirement> Requirements)
+      : TypeRef(TypeRefKind::ConstrainedExistential), Base(Protocol),
+        Requirements(Requirements) {}
 
   template <typename Allocator>
-  static const ParameterizedProtocolTypeRef *
+  static const ConstrainedExistentialTypeRef *
   create(Allocator &A, const ProtocolCompositionTypeRef *Protocol,
-         std::vector<const TypeRef *> Args) {
-    FIND_OR_CREATE_TYPEREF(A, ParameterizedProtocolTypeRef, Protocol, Args);
+         std::vector<TypeRefRequirement> Requirements) {
+    FIND_OR_CREATE_TYPEREF(A, ConstrainedExistentialTypeRef, Protocol,
+                           Requirements);
   }
 
   const ProtocolCompositionTypeRef *getBase() const { return Base; }
 
-  const std::vector<const TypeRef *> &getArgs() const { return Args; }
+  const std::vector<TypeRefRequirement> &getRequirements() const {
+    return Requirements;
+  }
 
   static bool classof(const TypeRef *TR) {
-    return TR->getKind() == TypeRefKind::ParameterizedProtocol;
+    return TR->getKind() == TypeRefKind::ConstrainedExistential;
   }
 };
 

include/swift/Reflection/TypeRefBuilder.h

@@ -650,13 +650,12 @@ class TypeRefBuilder {
                                               isClassBound);
   }
 
-  const ParameterizedProtocolTypeRef *
-  createParameterizedProtocolType(const TypeRef *base,
-                                  llvm::ArrayRef<const TypeRef *> args) {
+  const ConstrainedExistentialTypeRef *createConstrainedExistentialType(
+      const TypeRef *base, llvm::ArrayRef<BuiltRequirement> constraints) {
     auto *baseProto = llvm::dyn_cast<ProtocolCompositionTypeRef>(base);
     if (!baseProto)
       return nullptr;
-    return ParameterizedProtocolTypeRef::create(*this, baseProto, args);
+    return ConstrainedExistentialTypeRef::create(*this, baseProto, constraints);
   }
 
   const ExistentialMetatypeTypeRef *createExistentialMetatypeType(

include/swift/Reflection/TypeRefs.def

@@ -22,7 +22,7 @@ TYPEREF(BoundGeneric, TypeRef)
 TYPEREF(Tuple, TypeRef)
 TYPEREF(Function, TypeRef)
 TYPEREF(ProtocolComposition, TypeRef)
-TYPEREF(ParameterizedProtocol, TypeRef)
+TYPEREF(ConstrainedExistential, TypeRef)
 TYPEREF(Metatype, TypeRef)
 TYPEREF(ExistentialMetatype, TypeRef)
 TYPEREF(GenericTypeParameter, TypeRef)

lib/AST/ASTDemangler.cpp

@@ -625,12 +625,38 @@ Type ASTBuilder::createExistentialMetatypeType(Type instance,
                                       getMetatypeRepresentation(*repr));
 }
 
-Type ASTBuilder::createParameterizedProtocolType(Type base,
-                                                 ArrayRef<Type> args) {
+Type ASTBuilder::createConstrainedExistentialType(
+    Type base, ArrayRef<BuiltRequirement> constraints) {
+  // FIXME: Generalize to other kinds of bases.
   if (!base->getAs<ProtocolType>())
     return Type();
-  return ParameterizedProtocolType::get(base->getASTContext(),
-                                        base->castTo<ProtocolType>(), args);
+  auto baseTy = base->castTo<ProtocolType>();
+  auto baseDecl = baseTy->getDecl();
+  llvm::SmallDenseMap<Identifier, Type> cmap;
+  for (const auto &req : constraints) {
+    switch (req.getKind()) {
+    case RequirementKind::Conformance:
+    case RequirementKind::Superclass:
+    case RequirementKind::Layout:
+      continue;
+
+    case RequirementKind::SameType:
+      if (auto *DMT = req.getFirstType()->getAs<DependentMemberType>())
+        if (baseDecl->getAssociatedType(DMT->getName()))
+          cmap[DMT->getName()] = req.getSecondType();
+    }
+  }
+  llvm::SmallVector<Type, 4> args;
+  for (auto *assocTy : baseDecl->getPrimaryAssociatedTypes()) {
+    auto argTy = cmap.find(assocTy->getName());
+    if (argTy == cmap.end()) {
+      return Type();
+    }
+    args.push_back(argTy->getSecond());
+  }
+  auto constrainedBase =
+      ParameterizedProtocolType::get(base->getASTContext(), baseTy, args);
+  return ExistentialType::get(constrainedBase);
 }
 
 Type ASTBuilder::createMetatypeType(Type instance,