Structural opaque result types

CHANGELOG.md

@@ -3,6 +3,19 @@ CHANGELOG
 
 _**Note:** This is in reverse chronological order, so newer entries are added to the top._
 
+## Swift Next
+
+* [SE-0328][]:
+
+  Opaque types (expressed with 'some') can now be used in structural positions
+  within a result type, including having multiple opaque types in the same
+  result. For example:
+
+  ```
+  func getSomeDictionary() -> [some Hashable: some Codable] {
+    return [ 1: "One", 2: "Two" ]
+  }
+  ```
 Swift 5.6
 ---------
 
@@ -8761,6 +8774,7 @@ Swift 1.0
 [SE-0316]: <https://github.com/apple/swift-evolution/blob/main/proposals/0316-global-actors.md>
 [SE-0324]: <https://github.com/apple/swift-evolution/blob/main/proposals/0324-c-lang-pointer-arg-conversion.md>
 [SE-0323]: <https://github.com/apple/swift-evolution/blob/main/proposals/0323-async-main-semantics.md>
+[SE-0328]: <https://github.com/apple/swift-evolution/blob/main/proposals/0328-structural-opaque-result-types.md>
 
 [SR-75]: <https://bugs.swift.org/browse/SR-75>
 [SR-106]: <https://bugs.swift.org/browse/SR-106>

include/swift/AST/ASTMangler.h

@@ -339,7 +339,8 @@ class ASTMangler : public Mangler {
   }
 
   void appendBoundGenericArgs(Type type, GenericSignature sig,
-                              bool &isFirstArgList);
+                              bool &isFirstArgList,
+                              const ValueDecl *forDecl = nullptr);
 
   /// Append the bound generics arguments for the given declaration context
   /// based on a complete substitution map.
@@ -349,18 +350,21 @@ class ASTMangler : public Mangler {
   unsigned appendBoundGenericArgs(DeclContext *dc,
                                   GenericSignature sig,
                                   SubstitutionMap subs,
-                                  bool &isFirstArgList);
+                                  bool &isFirstArgList,
+                                  const ValueDecl *forDecl = nullptr);
 
   /// Append the bound generic arguments as a flat list, disregarding depth.
   void appendFlatGenericArgs(SubstitutionMap subs,
-                             GenericSignature sig);
+                             GenericSignature sig,
+                             const ValueDecl *forDecl = nullptr);
 
   /// Append any retroactive conformances.
   void appendRetroactiveConformances(Type type, GenericSignature sig);
   void appendRetroactiveConformances(SubstitutionMap subMap,
                                      GenericSignature sig,
                                      ModuleDecl *fromModule);
-  void appendImplFunctionType(SILFunctionType *fn, GenericSignature sig);
+  void appendImplFunctionType(SILFunctionType *fn, GenericSignature sig,
+                              const ValueDecl *forDecl = nullptr);
 
   void appendContextOf(const ValueDecl *decl);
 

include/swift/AST/Decl.h

@@ -2699,45 +2699,63 @@ class GenericTypeDecl : public GenericContext, public TypeDecl {
 /// The declared type uses a special kind of archetype type to represent
 /// abstracted types, e.g. `(some P, some Q)` becomes `((opaque archetype 0),
 /// (opaque archetype 1))`.
-class OpaqueTypeDecl : public GenericTypeDecl {
+class OpaqueTypeDecl final :
+    public GenericTypeDecl,
+    private llvm::TrailingObjects<OpaqueTypeDecl, OpaqueReturnTypeRepr *> {
+  friend TrailingObjects;
+
   /// The original declaration that "names" the opaque type. Although a specific
   /// opaque type cannot be explicitly named, oapque types can propagate
   /// arbitrarily through expressions, so we need to know *which* opaque type is
   /// propagated.
-  ValueDecl *NamingDecl;
+  ///
+  /// The bit indicates whether there are any trailing
+  /// OpaqueReturnTypeReprs.
+  llvm::PointerIntPair<ValueDecl *, 1>
+      NamingDeclAndHasOpaqueReturnTypeRepr;
 
   /// The generic signature of the opaque interface to the type. This is the
   /// outer generic signature with added generic parameters representing the
   /// abstracted underlying types.
   GenericSignature OpaqueInterfaceGenericSignature;
 
-  /// The type repr of the underlying type. Might be null if no source location
-  /// is availble, e.g. if this decl was loaded from a serialized module.
-  OpaqueReturnTypeRepr *UnderlyingInterfaceRepr;
-
-  /// The generic parameter that represents the underlying type.
-  GenericTypeParamType *UnderlyingInterfaceType;
-
   /// If known, the underlying type and conformances of the opaque type,
   /// expressed as a SubstitutionMap for the opaque interface generic signature.
   /// This maps types in the interface generic signature to the outer generic
   /// signature of the original declaration.
   Optional<SubstitutionMap> UnderlyingTypeSubstitutions;
 
   mutable Identifier OpaqueReturnTypeIdentifier;
-
-public:
+
   OpaqueTypeDecl(ValueDecl *NamingDecl, GenericParamList *GenericParams,
                  DeclContext *DC,
                  GenericSignature OpaqueInterfaceGenericSignature,
-                 OpaqueReturnTypeRepr *UnderlyingInterfaceRepr,
-                 GenericTypeParamType *UnderlyingInterfaceType);
+                 ArrayRef<OpaqueReturnTypeRepr *> OpaqueReturnTypeReprs);
+
+  unsigned getNumOpaqueReturnTypeReprs() const {
+    return NamingDeclAndHasOpaqueReturnTypeRepr.getInt()
+      ? getOpaqueGenericParams().size()
+      : 0;
+  }
+
+  size_t numTrailingObjects(OverloadToken<OpaqueReturnTypeRepr *>) const {
+    return getNumOpaqueReturnTypeReprs();
+  }
+
+public:
+  static OpaqueTypeDecl *get(
+      ValueDecl *NamingDecl, GenericParamList *GenericParams,
+      DeclContext *DC,
+      GenericSignature OpaqueInterfaceGenericSignature,
+      ArrayRef<OpaqueReturnTypeRepr *> OpaqueReturnTypeReprs);
 
-  ValueDecl *getNamingDecl() const { return NamingDecl; }
+  ValueDecl *getNamingDecl() const {
+    return NamingDeclAndHasOpaqueReturnTypeRepr.getPointer();
+  }
 
   void setNamingDecl(ValueDecl *D) {
-    assert(!NamingDecl && "already have naming decl");
-    NamingDecl = D;
+    assert(!getNamingDecl() && "already have naming decl");
+    NamingDeclAndHasOpaqueReturnTypeRepr.setPointer(D);
   }
 
   /// Is this opaque type the opaque return type of the given function?
@@ -2754,11 +2772,24 @@ class OpaqueTypeDecl : public GenericTypeDecl {
   GenericSignature getOpaqueInterfaceGenericSignature() const {
     return OpaqueInterfaceGenericSignature;
   }
-
-  GenericTypeParamType *getUnderlyingInterfaceType() const {
-    return UnderlyingInterfaceType;
+
+  /// Retrieve the generic parameters that represent the opaque types described by this opaque
+  /// type declaration.
+  TypeArrayView<GenericTypeParamType> getOpaqueGenericParams() const {
+    return OpaqueInterfaceGenericSignature.getInnermostGenericParams();
   }
-
+
+  /// Retrieve the buffer containing the opaque return type
+  /// representations that correspond to the opaque generic parameters.
+  ArrayRef<OpaqueReturnTypeRepr *> getOpaqueReturnTypeReprs() const {
+    return {
+      getTrailingObjects<OpaqueReturnTypeRepr *>(),
+      getNumOpaqueReturnTypeReprs()
+    };
+  }
+
+  /// The substitutions that map the generic parameters of the opaque type to
+  /// their underlying types, when that information is known.
   Optional<SubstitutionMap> getUnderlyingTypeSubstitutions() const {
     return UnderlyingTypeSubstitutions;
   }

include/swift/AST/DiagnosticsSema.def

@@ -1876,9 +1876,6 @@ ERROR(opaque_type_invalid_constraint,none,
       "and/or a base class", ())
 NOTE(opaque_of_optional_rewrite,none,
       "did you mean to write an optional of an 'opaque' type?", ())
-ERROR(more_than_one_opaque_type,none,
-      "%0 contains multiple 'opaque' types, but only one 'opaque' type is "
-      "supported", (TypeRepr*))
 ERROR(inferred_opaque_type,none,
       "property definition has inferred type %0, involving the 'some' "
       "return type of another declaration", (Type))
@@ -4135,8 +4132,8 @@ ERROR(opaque_type_no_underlying_type_candidates,none,
       "function declares an opaque return type, but has no return statements "
       "in its body from which to infer an underlying type", ())
 ERROR(opaque_type_mismatched_underlying_type_candidates,none,
-      "function declares an opaque return type, but the return statements "
-      "in its body do not have matching underlying types", ())
+      "function declares an opaque return type %0, but the return statements "
+      "in its body do not have matching underlying types", (TypeRepr *))
 NOTE(opaque_type_underlying_type_candidate_here,none,
      "return statement has underlying type %0", (Type))
 ERROR(opaque_type_self_referential_underlying_type,none,

include/swift/AST/Expr.h

@@ -3003,8 +3003,13 @@ class LinearToDifferentiableFunctionExpr : public ImplicitConversionExpr {
 /// (opaque type)" and "S<T> ---> S<(opaque type)>".
 class UnderlyingToOpaqueExpr : public ImplicitConversionExpr {
 public:
-  UnderlyingToOpaqueExpr(Expr *subExpr, Type ty)
-    : ImplicitConversionExpr(ExprKind::UnderlyingToOpaque, subExpr, ty) {}
+  /// The substitutions to be applied to the opaque type declaration to
+  /// produce the resulting type.
+  const SubstitutionMap substitutions;
+
+  UnderlyingToOpaqueExpr(Expr *subExpr, Type ty, SubstitutionMap substitutions)
+    : ImplicitConversionExpr(ExprKind::UnderlyingToOpaque, subExpr, ty),
+      substitutions(substitutions) {}
 
   static bool classof(const Expr *E) {
     return E->getKind() == ExprKind::UnderlyingToOpaque;

include/swift/AST/Types.h

@@ -5601,17 +5601,15 @@ class OpaqueTypeArchetypeType final : public ArchetypeType,
   ///   func foo() -> (some P, some Q)
   ///
   /// then the underlying type of `some P` would be ordinal 0, and `some Q` would be ordinal 1.
-  unsigned getOrdinal() const {
-    // TODO [OPAQUE SUPPORT]: multiple opaque types
-    return 0;
-  }
+  unsigned getOrdinal() const;
 
   static void Profile(llvm::FoldingSetNodeID &ID,
                       OpaqueTypeDecl *OpaqueDecl,
+                      unsigned ordinal,
                       SubstitutionMap Substitutions);
 
   void Profile(llvm::FoldingSetNodeID &ID) {
-    Profile(ID, getDecl(), getSubstitutions());
+    Profile(ID, getDecl(), getOrdinal(), getSubstitutions());
   };
 
 private:

include/swift/Option/FrontendOptions.td

@@ -486,10 +486,6 @@ def enable_experimental_named_opaque_types :
   Flag<["-"], "enable-experimental-named-opaque-types">,
   HelpText<"Enable experimental support for named opaque result types">;
 
-def enable_experimental_structural_opaque_types :
-  Flag<["-"], "enable-experimental-structural-opaque-types">,
-  HelpText<"Enable experimental support for structural opaque result types">;
-
 def enable_explicit_existential_types :
   Flag<["-"], "enable-explicit-existential-types">,
   HelpText<"Enable experimental support for explicit existential types">;

include/swift/Sema/ConstraintSystem.h

@@ -3316,6 +3316,11 @@ class ConstraintSystem {
                        ArrayRef<ConstraintLocator::PathElement> path,
                        unsigned summaryFlags);
 
+  /// Retrieve a locator for opening the opaque archetype for the given
+  /// opaque type.
+  ConstraintLocator *getOpenOpaqueLocator(
+      ConstraintLocatorBuilder locator, OpaqueTypeDecl *opaqueDecl);
+
   /// Retrive the constraint locator for the given anchor and
   /// path, uniqued and automatically infer the summary flags
   ConstraintLocator *

lib/APIDigester/ModuleAnalyzerNodes.cpp

@@ -1510,18 +1510,18 @@ SDKNode *swift::ide::api::
 SwiftDeclCollector::constructTypeNode(Type T, TypeInitInfo Info) {
   if (Ctx.checkingABI()) {
     T = T->getCanonicalType();
-    // If the type is a opaque result type (some Type) and we're in the ABI mode,
-    // we should substitute the opaque result type to its underlying type.
-    // Notice this only works if the opaque result type is from an inlinable
-    // function where the function body is present in the swift module file, thus
-    // allowing us to know the concrete type.
-    if (auto OTA = T->getAs<OpaqueTypeArchetypeType>()) {
-      if (auto *D = OTA->getDecl()) {
-        if (auto SubMap = D->getUnderlyingTypeSubstitutions()) {
-          T = Type(D->getUnderlyingInterfaceType()).
-            subst(*SubMap)->getCanonicalType();
-        }
-      }
+
+    if (T->hasOpaqueArchetype()) {
+      // When the type contains an opaque result type and we're in the ABI mode,
+      // we should substitute the opaque result type to its underlying type.
+      // Notice this only works if the opaque result type is from an inlinable
+      // function where the function body is present in the swift module file,
+      // thus allowing us to know the concrete type.
+      ReplaceOpaqueTypesWithUnderlyingTypes replacer(
+          /*inContext=*/nullptr, ResilienceExpansion::Maximal,
+          /*isWholeModuleContext=*/false);
+      T = T.subst(replacer, replacer, SubstFlags::SubstituteOpaqueArchetypes)
+          ->getCanonicalType();
     }
   }
 

lib/AST/ASTContext.cpp

@@ -4275,17 +4275,15 @@ DependentMemberType *DependentMemberType::get(Type base,
 OpaqueTypeArchetypeType *
 OpaqueTypeArchetypeType::get(OpaqueTypeDecl *Decl, unsigned ordinal,
                              SubstitutionMap Substitutions) {
-  // TODO [OPAQUE SUPPORT]: multiple opaque types
-  assert(ordinal == 0 && "we only support one 'some' type per composite type");
-  auto opaqueParamType = Decl->getUnderlyingInterfaceType();
+  auto opaqueParamType = Decl->getOpaqueGenericParams()[ordinal];
 
   // TODO: We could attempt to preserve type sugar in the substitution map.
   // Currently archetypes are assumed to be always canonical in many places,
   // though, so doing so would require fixing those places.
   Substitutions = Substitutions.getCanonical();
 
   llvm::FoldingSetNodeID id;
-  Profile(id, Decl, Substitutions);
+  Profile(id, Decl, ordinal, Substitutions);
 
   auto &ctx = Decl->getASTContext();
 

lib/AST/ASTDemangler.cpp

@@ -265,11 +265,6 @@ Type ASTBuilder::resolveOpaqueType(NodePointer opaqueDescriptor,
     auto opaqueDecl = parentModule->lookupOpaqueResultType(mangledName);
     if (!opaqueDecl)
       return Type();
-    // TODO [OPAQUE SUPPORT]: multiple opaque types
-    assert(ordinal == 0 && "not implemented");
-    if (ordinal != 0)
-      return Type();
-
     SmallVector<Type, 8> allArgs;
     for (auto argSet : args) {
       allArgs.append(argSet.begin(), argSet.end());

lib/AST/ASTDumper.cpp

@@ -567,7 +567,7 @@ namespace {
       OS << " naming_decl=";
       printDeclName(OTD->getNamingDecl());
       PrintWithColorRAII(OS, TypeColor) << " opaque_interface="
-        << Type(OTD->getUnderlyingInterfaceType()).getString();
+        << OTD->getDeclaredInterfaceType().getString();
       OS << " in "
          << OTD->getOpaqueInterfaceGenericSignature()->getAsString();
       if (auto underlyingSubs = OTD->getUnderlyingTypeSubstitutions()) {
@@ -3776,6 +3776,7 @@ namespace {
                                       StringRef label) {
       printArchetypeCommon(T, "opaque_type", label);
       printField("decl", T->getDecl()->getNamingDecl()->printRef());
+      printField("ordinal", T->getOrdinal());
       if (!T->getSubstitutions().empty()) {
         OS << '\n';
         SmallPtrSet<const ProtocolConformance *, 4> Dumped;