Add support for opaque result types in structural positions

include/swift/AST/Decl.h

@@ -2537,7 +2537,10 @@ class ValueDecl : public Decl {
   OpaqueTypeDecl *getOpaqueResultTypeDecl() const;
 
   /// Get the representative for this value's opaque result type, if it has one.
-  OpaqueReturnTypeRepr *getOpaqueResultTypeRepr() const;
+  /// Returns a `TypeRepr` instead of an `OpaqueReturnTypeRepr` because 'some'
+  /// types might appear in one or more structural positions, e.g.  (some P,
+  /// some Q), or we might have a `NamedOpaqueReturnTypeRepr`.
+  TypeRepr *getOpaqueResultTypeRepr() const;
 
   /// Retrieve the attribute associating this declaration with a
   /// result builder, if there is one.
@@ -2629,26 +2632,30 @@ class GenericTypeDecl : public GenericContext, public TypeDecl {
 /// clients of the opaque type, only exposing the type as something conforming
 /// to a given set of constraints.
 ///
-/// Currently, opaque types do not normally have an explicit spelling in source
-/// code. One is formed implicitly when a declaration is written with an opaque
-/// result type, as in:
+/// An `OpaqueTypeDecl` is formed implicitly when a declaration is written with
+/// an opaque result type, as in the following example:
 ///
 /// func foo() -> some SignedInteger { return 1 }
 ///
-/// The declared type is a special kind of ArchetypeType representing the
-/// abstracted underlying type.
+/// 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 {
   /// 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 generic signature of the opaque interface to the type. This is the
-  /// outer generic signature with an added generic parameter representing the
-  /// underlying type.
+  /// 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;
 
@@ -2661,12 +2668,12 @@ class OpaqueTypeDecl : public GenericTypeDecl {
   mutable Identifier OpaqueReturnTypeIdentifier;
 
 public:
-  OpaqueTypeDecl(ValueDecl *NamingDecl,
-                 GenericParamList *GenericParams,
+  OpaqueTypeDecl(ValueDecl *NamingDecl, GenericParamList *GenericParams,
                  DeclContext *DC,
                  GenericSignature OpaqueInterfaceGenericSignature,
+                 OpaqueReturnTypeRepr *UnderlyingInterfaceRepr,
                  GenericTypeParamType *UnderlyingInterfaceType);
-  
+
   ValueDecl *getNamingDecl() const { return NamingDecl; }
 
   void setNamingDecl(ValueDecl *D) {
@@ -2680,6 +2687,11 @@ class OpaqueTypeDecl : public GenericTypeDecl {
   /// function could also be the getter of a storage declaration.
   bool isOpaqueReturnTypeOfFunction(const AbstractFunctionDecl *func) const;
 
+  /// Get the ordinal of the anonymous opaque parameter of this decl with type
+  /// repr `repr`, as introduce implicitly by an occurrence of "some" in return
+  /// position e.g. `func f() -> some P`. Returns -1 if `repr` is not found.
+  unsigned getAnonymousOpaqueParamOrdinal(OpaqueReturnTypeRepr *repr) const;
+
   GenericSignature getOpaqueInterfaceGenericSignature() const {
     return OpaqueInterfaceGenericSignature;
   }

include/swift/AST/DiagnosticsSema.def

@@ -1862,6 +1862,11 @@ WARNING(spi_attribute_on_import_of_public_module,none,
 ERROR(opaque_type_invalid_constraint,none,
       "an 'opaque' type must specify only 'Any', 'AnyObject', protocols, "
       "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))
@@ -4060,9 +4065,6 @@ WARNING(trailing_closure_requires_parens,none,
         " statement; pass as a parenthesized argument to silence this warning",
         ())
 
-ERROR(opaque_type_var_no_init,none,
-      "property declares an opaque return type, but has no initializer "
-      "expression from which to infer an underlying type", ())
 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", ())
@@ -4074,6 +4076,9 @@ NOTE(opaque_type_underlying_type_candidate_here,none,
 ERROR(opaque_type_self_referential_underlying_type,none,
       "function opaque return type was inferred as %0, which defines the "
       "opaque type in terms of itself", (Type))
+ERROR(opaque_type_var_no_init,none,
+      "property declares an opaque return type, but has no initializer "
+      "expression from which to infer an underlying type", ())
 ERROR(opaque_type_var_no_underlying_type,none,
       "property declares an opaque return type, but cannot infer the "
       "underlying type from its initializer expression", ())

include/swift/AST/Expr.h

@@ -3193,8 +3193,9 @@ class LinearToDifferentiableFunctionExpr : public ImplicitConversionExpr {
   }
 };
 
-
-/// Use an opaque type to abstract a value of the underlying concrete type.
+/// Use an opaque type to abstract a value of the underlying concrete type,
+/// possibly nested inside other types. E.g. can perform coversions "T --->
+/// (opaque type)" and "S<T> ---> S<(opaque type)>".
 class UnderlyingToOpaqueExpr : public ImplicitConversionExpr {
 public:
   UnderlyingToOpaqueExpr(Expr *subExpr, Type ty)

include/swift/AST/TypeRepr.h

@@ -150,6 +150,20 @@ class alignas(1 << TypeReprAlignInBits) TypeRepr {
     return walk(walker);
   }
 
+  /// Look through the given type and its children to find a type for
+  /// which the given predicate returns true.
+  ///
+  /// \param pred A predicate function object. It should return true if the
+  /// given type node satisfies the criteria.
+  ///
+  /// \returns true if the predicate returns true for the given type or any of
+  /// its children.
+  bool findIf(llvm::function_ref<bool(TypeRepr *)> pred);
+
+  /// Check recursively whether this type repr or any of its decendants are
+  /// opaque return type reprs.
+  bool hasOpaque();
+
   //*** Allocation Routines ************************************************/
 
   void *operator new(size_t bytes, const ASTContext &C,
@@ -1108,9 +1122,9 @@ class OpaqueReturnTypeRepr : public TypeRepr {
 /// A TypeRepr for a type with a generic parameter list of named opaque return
 /// types.
 ///
-/// This can occur only as the return type of a function declaration, to specify
-/// subtypes which should be abstracted from callers, given a set of generic
-/// constraints that the concrete types satisfy:
+/// This can occur only as the return type of a function declaration, or the
+/// type of a property, to specify types which should be abstracted from
+/// callers, given a set of generic constraints that the concrete types satisfy:
 ///
 /// func foo() -> <T: Collection> T { return [1] }
 class NamedOpaqueReturnTypeRepr : public TypeRepr {

include/swift/AST/Types.h

@@ -5472,13 +5472,13 @@ class OpaqueTypeArchetypeType final : public ArchetypeType,
   GenericEnvironment *Environment;
 
 public:
-  /// Get 
-
   /// Get an opaque archetype representing the underlying type of the given
-  /// opaque type decl.
-  static OpaqueTypeArchetypeType *get(OpaqueTypeDecl *Decl,
+  /// opaque type decl's opaque param with ordinal `ordinal`. For example, in
+  /// `(some P, some Q)`, `some P`'s type param would have ordinal 0 and `some
+  /// Q`'s type param would have ordinal 1.
+  static OpaqueTypeArchetypeType *get(OpaqueTypeDecl *Decl, unsigned ordinal,
                                       SubstitutionMap Substitutions);
-  
+
   OpaqueTypeDecl *getDecl() const {
     return OpaqueDecl;
   }
@@ -5509,7 +5509,7 @@ class OpaqueTypeArchetypeType final : public ArchetypeType,
   ///
   /// then the underlying type of `some P` would be ordinal 0, and `some Q` would be ordinal 1.
   unsigned getOrdinal() const {
-    // TODO: multiple opaque types
+    // TODO [OPAQUE SUPPORT]: multiple opaque types
     return 0;
   }
 

include/swift/Sema/Constraint.h

@@ -154,9 +154,6 @@ enum class ConstraintKind : char {
   /// The first type is a function type, the second is the function's
   /// result type.
   FunctionResult,
-  /// The first type is a type that's a candidate to be the underlying type of
-  /// the second opaque archetype.
-  OpaqueUnderlyingType,
   /// The first type will be equal to the second type, but only when the
   /// second type has been fully determined (and mapped down to a concrete
   /// type). At that point, this constraint will be treated like an `Equal`
@@ -604,7 +601,6 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     case ConstraintKind::DynamicCallableApplicableFunction:
     case ConstraintKind::BindOverload:
     case ConstraintKind::OptionalObject:
-    case ConstraintKind::OpaqueUnderlyingType:
     case ConstraintKind::OneWayEqual:
     case ConstraintKind::OneWayBindParam:
     case ConstraintKind::DefaultClosureType:

include/swift/Sema/ConstraintLocator.h

@@ -785,6 +785,19 @@ class LocatorPathElt::OpenedGeneric final : public StoredPointerElement<GenericS
   }
 };
 
+class LocatorPathElt::OpenedOpaqueArchetype final
+    : public StoredPointerElement<OpaqueTypeDecl> {
+public:
+  OpenedOpaqueArchetype(OpaqueTypeDecl *decl)
+      : StoredPointerElement(PathElementKind::OpenedOpaqueArchetype, decl) {}
+
+  OpaqueTypeDecl *getDecl() const { return getStoredPointer(); }
+
+  static bool classof(const LocatorPathElt *elt) {
+    return elt->getKind() == ConstraintLocator::OpenedOpaqueArchetype;
+  }
+};
+
 class LocatorPathElt::KeyPathDynamicMember final : public StoredPointerElement<NominalTypeDecl> {
 public:
   KeyPathDynamicMember(NominalTypeDecl *keyPathDecl)

include/swift/Sema/ConstraintLocatorPathElts.def

@@ -134,6 +134,10 @@ SIMPLE_LOCATOR_PATH_ELT(MemberRefBase)
 /// base of the locator.
 CUSTOM_LOCATOR_PATH_ELT(OpenedGeneric)
 
+/// This is referring to a type produced by opening an opaque type archetype
+/// type at the base of the locator.
+CUSTOM_LOCATOR_PATH_ELT(OpenedOpaqueArchetype)
+
 /// An optional payload.
 SIMPLE_LOCATOR_PATH_ELT(OptionalPayload)
 

include/swift/Sema/ConstraintSystem.h

@@ -792,7 +792,7 @@ struct AppliedBuilderTransform {
   Type builderType;
 
   /// The result type of the body, to which the returned expression will be
-  /// converted.
+  /// converted. Opaque types should be unopened.
   Type bodyResultType;
 
   /// An expression whose value has been recorded for later use.
@@ -3318,9 +3318,8 @@ class ConstraintSystem {
                      bool isFavored = false);
 
   /// Add the appropriate constraint for a contextual conversion.
-  void addContextualConversionConstraint(
-      Expr *expr, Type conversionType, ContextualTypePurpose purpose,
-      bool isOpaqueReturnType);
+  void addContextualConversionConstraint(Expr *expr, Type conversionType,
+                                         ContextualTypePurpose purpose);
 
   /// Convenience function to pass an \c ArrayRef to \c addJoinConstraint
   Type addJoinConstraint(ConstraintLocator *locator,
@@ -3856,6 +3855,12 @@ class ConstraintSystem {
   /// \returns The opened type, or \c type if there are no archetypes in it.
   Type openType(Type type, OpenedTypeMap &replacements);
 
+  /// "Open" an opaque archetype type.
+  Type openOpaqueType(Type type, ConstraintLocatorBuilder locator);
+
+  /// Recurse over the given type and open any opaque archetype types.
+  Type openOpaqueTypeRec(Type type, ConstraintLocatorBuilder locator);
+
   /// "Open" the given function type.
   ///
   /// If the function type is non-generic, this is equivalent to calling
@@ -4593,12 +4598,6 @@ class ConstraintSystem {
                                           TypeMatchOptions flags,
                                           ConstraintLocatorBuilder locator);
 
-  /// Attempt to simplify an OpaqueUnderlyingType constraint.
-  SolutionKind simplifyOpaqueUnderlyingTypeConstraint(Type type1,
-                                              Type type2,
-                                              TypeMatchOptions flags,
-                                              ConstraintLocatorBuilder locator);
-
   /// Attempt to simplify the BridgingConversion constraint.
   SolutionKind simplifyBridgingConstraint(Type type1,
                                          Type type2,
@@ -4729,10 +4728,10 @@ class ConstraintSystem {
   ///
   /// \returns \c None when the result builder cannot be applied at all,
   /// otherwise the result of applying the result builder.
-  Optional<TypeMatchResult> matchResultBuilder(
-      AnyFunctionRef fn, Type builderType, Type bodyResultType,
-      ConstraintKind bodyResultConstraintKind,
-      ConstraintLocatorBuilder locator);
+  Optional<TypeMatchResult>
+  matchResultBuilder(AnyFunctionRef fn, Type builderType, Type bodyResultType,
+                     ConstraintKind bodyResultConstraintKind,
+                     ConstraintLocatorBuilder locator);
 
   /// Matches a wrapped or projected value parameter type to its backing
   /// property wrapper type by applying the property wrapper.

lib/AST/ASTContext.cpp

@@ -4159,9 +4159,12 @@ DependentMemberType *DependentMemberType::get(Type base,
 }
 
 OpaqueTypeArchetypeType *
-OpaqueTypeArchetypeType::get(OpaqueTypeDecl *Decl,
-                             SubstitutionMap Substitutions)
-{
+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();
+
   // 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.
@@ -4237,18 +4240,18 @@ OpaqueTypeArchetypeType::get(OpaqueTypeDecl *Decl,
     }
   }
 #else
-  // Assert that there are no same type constraints on the underlying type
-  // or its associated types.
+  // Assert that there are no same type constraints on the opaque type or its
+  // associated types.
   //
   // This should not be possible until we add where clause support, with the
   // exception of generic base class constraints (handled below).
   (void)newRequirements;
 # ifndef NDEBUG
-  for (auto reqt :
+  for (auto req :
                 Decl->getOpaqueInterfaceGenericSignature().getRequirements()) {
-    auto reqtBase = reqt.getFirstType()->getRootGenericParam();
-    if (reqtBase->isEqual(Decl->getUnderlyingInterfaceType())) {
-      assert(reqt.getKind() != RequirementKind::SameType
+    auto reqBase = req.getFirstType()->getRootGenericParam();
+    if (reqBase->isEqual(opaqueParamType)) {
+      assert(req.getKind() != RequirementKind::SameType
              && "supporting where clauses on opaque types requires correctly "
                 "setting up the generic environment for "
                 "OpaqueTypeArchetypeTypes; see comment above");
@@ -4264,9 +4267,8 @@ OpaqueTypeArchetypeType::get(OpaqueTypeDecl *Decl,
         std::move(newRequirements)},
       nullptr);
 
-  auto opaqueInterfaceTy = Decl->getUnderlyingInterfaceType();
-  auto layout = signature->getLayoutConstraint(opaqueInterfaceTy);
-  auto superclass = signature->getSuperclassBound(opaqueInterfaceTy);
+  auto reqs = signature->getLocalRequirements(opaqueParamType);
+  auto superclass = reqs.superclass;
   #if !DO_IT_CORRECTLY
     // Ad-hoc substitute the generic parameters of the superclass.
     // If we correctly applied the substitutions to the generic signature
@@ -4275,25 +4277,23 @@ OpaqueTypeArchetypeType::get(OpaqueTypeDecl *Decl,
       superclass = superclass.subst(Substitutions);
     }
   #endif
-  const auto protos = signature->getRequiredProtocols(opaqueInterfaceTy);
 
   auto mem = ctx.Allocate(
     OpaqueTypeArchetypeType::totalSizeToAlloc<ProtocolDecl *, Type, LayoutConstraint>(
-      protos.size(), superclass ? 1 : 0, layout ? 1 : 0),
+      reqs.protos.size(), superclass ? 1 : 0, reqs.layout ? 1 : 0),
       alignof(OpaqueTypeArchetypeType),
       arena);
-
-  auto newOpaque = ::new (mem) OpaqueTypeArchetypeType(Decl, Substitutions,
-                                                    properties,
-                                                    opaqueInterfaceTy,
-                                                    protos, superclass, layout);
-
+
+  auto newOpaque = ::new (mem)
+      OpaqueTypeArchetypeType(Decl, Substitutions, properties, opaqueParamType,
+                              reqs.protos, superclass, reqs.layout);
+
   // Create a generic environment and bind the opaque archetype to the
   // opaque interface type from the decl's signature.
   auto *env = GenericEnvironment::getIncomplete(signature);
-  env->addMapping(GenericParamKey(opaqueInterfaceTy), newOpaque);
+  env->addMapping(GenericParamKey(opaqueParamType), newOpaque);
   newOpaque->Environment = env;
-  
+
   // Look up the insertion point in the folding set again in case something
   // invalidated it above.
   {
@@ -4303,7 +4303,7 @@ OpaqueTypeArchetypeType::get(OpaqueTypeDecl *Decl,
     assert(!existing && "race to create opaque archetype?!");
     set.InsertNode(newOpaque, insertPos);
   }
-  
+
   return newOpaque;
 }