Opaque parameters

include/swift/AST/Decl.h

@@ -492,12 +492,15 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
   SWIFT_INLINE_BITFIELD_EMPTY(TypeDecl, ValueDecl);
   SWIFT_INLINE_BITFIELD_EMPTY(AbstractTypeParamDecl, TypeDecl);
 
-  SWIFT_INLINE_BITFIELD_FULL(GenericTypeParamDecl, AbstractTypeParamDecl, 16+16+1,
+  SWIFT_INLINE_BITFIELD_FULL(GenericTypeParamDecl, AbstractTypeParamDecl, 16+16+1+1,
     : NumPadBits,
 
     Depth : 16,
     Index : 16,
-    TypeSequence : 1
+    TypeSequence : 1,
+
+    /// Whether this generic parameter represents an opaque type.
+    IsOpaqueType : 1
   );
 
   SWIFT_INLINE_BITFIELD_EMPTY(GenericTypeDecl, TypeDecl);
@@ -2786,7 +2789,8 @@ class OpaqueTypeDecl final :
   /// 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;
+  Optional<unsigned> getAnonymousOpaqueParamOrdinal(
+      OpaqueReturnTypeRepr *repr) const;
 
   GenericSignature getOpaqueInterfaceGenericSignature() const {
     return OpaqueInterfaceGenericSignature;
@@ -2993,9 +2997,14 @@ class AbstractTypeParamDecl : public TypeDecl {
 /// \code
 /// func min<T : Comparable>(x : T, y : T) -> T { ... }
 /// \endcode
-class GenericTypeParamDecl : public AbstractTypeParamDecl {
-public:
-  static const unsigned InvalidDepth = 0xFFFF;
+class GenericTypeParamDecl final :
+    public AbstractTypeParamDecl,
+    private llvm::TrailingObjects<GenericTypeParamDecl, OpaqueReturnTypeRepr *>{
+  friend TrailingObjects;
+
+  size_t numTrailingObjects(OverloadToken<OpaqueReturnTypeRepr *>) const {
+    return isOpaqueType() ? 1 : 0;
+  }
 
   /// Construct a new generic type parameter.
   ///
@@ -3006,7 +3015,29 @@ class GenericTypeParamDecl : public AbstractTypeParamDecl {
   /// \param name The name of the generic parameter.
   /// \param nameLoc The location of the name.
   GenericTypeParamDecl(DeclContext *dc, Identifier name, SourceLoc nameLoc,
-                       bool isTypeSequence, unsigned depth, unsigned index);
+                       bool isTypeSequence, unsigned depth, unsigned index,
+                       bool isOpaqueType, OpaqueReturnTypeRepr *opaqueTypeRepr);
+
+public:
+  /// Construct a new generic type parameter.
+  ///
+  /// \param dc The DeclContext in which the generic type parameter's owner
+  /// occurs. This should later be overwritten with the actual declaration
+  /// context that owns the type parameter.
+  ///
+  /// \param name The name of the generic parameter.
+  /// \param nameLoc The location of the name.
+  GenericTypeParamDecl(DeclContext *dc, Identifier name, SourceLoc nameLoc,
+                       bool isTypeSequence, unsigned depth, unsigned index)
+      : GenericTypeParamDecl(dc, name, nameLoc, isTypeSequence, depth, index,
+                             false, nullptr) { }
+
+  static const unsigned InvalidDepth = 0xFFFF;
+
+  static GenericTypeParamDecl *
+  create(DeclContext *dc, Identifier name, SourceLoc nameLoc,
+         bool isTypeSequence, unsigned depth, unsigned index,
+         bool isOpaqueType, OpaqueReturnTypeRepr *opaqueTypeRepr);
 
   /// The depth of this generic type parameter, i.e., the number of outer
   /// levels of generic parameter lists that enclose this type parameter.
@@ -3034,9 +3065,33 @@ class GenericTypeParamDecl : public AbstractTypeParamDecl {
   /// \code
   /// func foo<@_typeSequence T>(_ : T...) { }
   /// struct Foo<@_typeSequence T> { }
-  /// \encode
+  /// \endcode
   bool isTypeSequence() const { return Bits.GenericTypeParamDecl.TypeSequence; }
 
+  /// Determine whether this generic parameter represents an opaque type.
+  ///
+  /// \code
+  /// // "some P" is representated by a generic type parameter.
+  /// func f() -> [some P] { ... }
+  /// \endcode
+  bool isOpaqueType() const {
+    return Bits.GenericTypeParamDecl.IsOpaqueType;
+  }
+
+  /// Retrieve the opaque return type representation described by this
+  /// generic parameter, or NULL if any of the following are true:
+  ///   - the generic parameter does not describe an opaque type
+  ///   - the opaque type was introduced via the "named opaque parameters"
+  ///     extension, meaning that it was specified explicitly
+  ///   - the enclosing declaration was deserialized, in which case it lost
+  ///     the source location information and has no type representation.
+  OpaqueReturnTypeRepr *getOpaqueTypeRepr() const {
+    if (!isOpaqueType())
+      return nullptr;
+
+    return *getTrailingObjects<OpaqueReturnTypeRepr *>();
+  }
+
   /// The index of this generic type parameter within its generic parameter
   /// list.
   ///

include/swift/AST/TypeRepr.h

@@ -47,6 +47,9 @@ enum class TypeReprKind : uint8_t {
 enum : unsigned { NumTypeReprKindBits =
   countBitsUsed(static_cast<unsigned>(TypeReprKind::Last_TypeRepr)) };
 
+class OpaqueReturnTypeRepr;
+using CollectedOpaqueReprs = SmallVector<OpaqueReturnTypeRepr *, 2>;
+
 /// Representation of a type as written in source.
 class alignas(1 << TypeReprAlignInBits) TypeRepr
     : public ASTAllocated<TypeRepr> {
@@ -165,6 +168,10 @@ class alignas(1 << TypeReprAlignInBits) TypeRepr
   /// opaque return type reprs.
   bool hasOpaque();
 
+  /// Walk the type representation recursively, collecting any
+  /// `OpaqueReturnTypeRepr`s.
+  CollectedOpaqueReprs collectOpaqueReturnTypeReprs();
+
   //*** Allocation Routines ************************************************/
 
   void print(raw_ostream &OS, const PrintOptions &Opts = PrintOptions()) const;

include/swift/Basic/LangOptions.h

@@ -313,6 +313,10 @@ namespace swift {
     /// `func f() -> <T> T`.
     bool EnableExperimentalNamedOpaqueTypes = false;
 
+    /// Enable experimental support for opaque parameter types, e.g.
+    /// `func f(collection: some Collection)`.
+    bool EnableExperimentalOpaqueParameters = false;
+
     /// Enable support for explicit existential types via the \c any
     /// keyword.
     bool EnableExplicitExistentialTypes = true;

include/swift/Option/FrontendOptions.td

@@ -295,6 +295,10 @@ def enable_experimental_eager_clang_module_diagnostics :
   Flag<["-"], "enable-experimental-eager-clang-module-diagnostics">,
   HelpText<"Enable experimental eager diagnostics reporting on the importability of all referenced C, C++, and Objective-C libraries">;
 
+def enable_experimental_opaque_parameters :
+  Flag<["-"], "enable-experimental-opaque-parameters">,
+  HelpText<"Enable experimental support for opaque parameters">;
+
 def enable_experimental_pairwise_build_block :
   Flag<["-"], "enable-experimental-pairwise-build-block">,
   HelpText<"Enable experimental pairwise 'buildBlock' for result builders">;

lib/AST/ASTPrinter.cpp

@@ -1658,7 +1658,42 @@ void PrintAST::printSingleDepthOfGenericSignature(
       });
   };
 
-  if (printParams) {
+  /// Separate the explicit generic parameters from the implicit, opaque
+  /// generic parameters. We only print the former.
+  TypeArrayView<GenericTypeParamType> opaqueGenericParams;
+  for (unsigned index : indices(genericParams)) {
+    auto gpDecl = genericParams[index]->getDecl();
+    if (!gpDecl)
+      continue;
+
+    if (gpDecl->isOpaqueType() && gpDecl->isImplicit()) {
+      // We found the first implicit opaque type parameter. Split the
+      // generic parameters array at this position.
+      opaqueGenericParams = genericParams.slice(index);
+      genericParams = genericParams.slice(0, index);
+      break;
+    }
+  }
+
+  // Determines whether a given type is based on one of the opaque generic
+  // parameters.
+  auto dependsOnOpaque = [&](Type type) {
+    if (opaqueGenericParams.empty())
+      return false;
+
+    if (!type->isTypeParameter())
+      return false;
+
+    auto rootGP = type->getRootGenericParam();
+    for (auto opaqueGP : opaqueGenericParams) {
+      if (rootGP->isEqual(opaqueGP))
+        return true;
+    }
+
+    return false;
+  };
+
+  if (printParams && !genericParams.empty()) {
     // Print the generic parameters.
     Printer << "<";
     llvm::interleave(
@@ -1686,10 +1721,17 @@ void PrintAST::printSingleDepthOfGenericSignature(
         continue;
 
       auto first = req.getFirstType();
+
+      if (dependsOnOpaque(first))
+        continue;
+
       Type second;
 
-      if (req.getKind() != RequirementKind::Layout)
+      if (req.getKind() != RequirementKind::Layout) {
         second = req.getSecondType();
+        if (dependsOnOpaque(second))
+          continue;
+      }
 
       if (!subMap.empty()) {
         Type subFirst = substParam(first);
@@ -1748,7 +1790,7 @@ void PrintAST::printSingleDepthOfGenericSignature(
     }
   }
 
-  if (printParams)
+  if (printParams && !genericParams.empty())
     Printer << ">";
 }
 
@@ -6031,7 +6073,8 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
   }
 
   void visitGenericTypeParamType(GenericTypeParamType *T) {
-    if (T->getDecl() == nullptr) {
+    auto decl = T->getDecl();
+    if (!decl) {
       // If we have an alternate name for this type, use it.
       if (Options.AlternativeTypeNames) {
         auto found = Options.AlternativeTypeNames->find(T->getCanonicalType());
@@ -6047,6 +6090,25 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
         T = Options.GenericSig->getSugaredType(T);
     }
 
+    // Print opaque types as "some ..."
+    if (decl && decl->isOpaqueType()) {
+      // If we have and should print based on the type representation, do so.
+      if (auto opaqueRepr = decl->getOpaqueTypeRepr()) {
+        if (willUseTypeReprPrinting(opaqueRepr, Type(), Options)) {
+          opaqueRepr->print(Printer, Options);
+          return;
+        }
+      }
+
+      // Print based on the type.
+      Printer << "some ";
+      if (auto inheritedType = decl->getInherited().front().getType())
+        inheritedType->print(Printer, Options);
+      else
+        Printer << "Any";
+      return;
+    }
+
     const auto Name = T->getName();
     if (Name.empty()) {
       Printer << "<anonymous>";

lib/AST/Builtins.cpp

@@ -234,9 +234,9 @@ static GenericTypeParamDecl*
 createGenericParam(ASTContext &ctx, const char *name, unsigned index) {
   ModuleDecl *M = ctx.TheBuiltinModule;
   Identifier ident = ctx.getIdentifier(name);
-  auto genericParam = new (ctx) GenericTypeParamDecl(
+  auto genericParam = GenericTypeParamDecl::create(
       &M->getMainFile(FileUnitKind::Builtin), ident, SourceLoc(),
-      /*type sequence*/ false, 0, index);
+      /*type sequence*/ false, 0, index, /*opaque type=*/false, nullptr);
   return genericParam;
 }
 

lib/AST/Decl.cpp

@@ -4102,16 +4102,21 @@ AbstractTypeParamDecl::getConformingProtocols() const {
   return { };
 }
 
-GenericTypeParamDecl::GenericTypeParamDecl(DeclContext *dc, Identifier name,
-                                           SourceLoc nameLoc,
-                                           bool isTypeSequence, unsigned depth,
-                                           unsigned index)
-    : AbstractTypeParamDecl(DeclKind::GenericTypeParam, dc, name, nameLoc) {
+GenericTypeParamDecl::GenericTypeParamDecl(
+    DeclContext *dc, Identifier name, SourceLoc nameLoc,
+    bool isTypeSequence, unsigned depth, unsigned index,
+    bool isOpaqueType, OpaqueReturnTypeRepr *opaqueTypeRepr
+  ) : AbstractTypeParamDecl(DeclKind::GenericTypeParam, dc, name, nameLoc) {
   Bits.GenericTypeParamDecl.Depth = depth;
   assert(Bits.GenericTypeParamDecl.Depth == depth && "Truncation");
   Bits.GenericTypeParamDecl.Index = index;
   assert(Bits.GenericTypeParamDecl.Index == index && "Truncation");
   Bits.GenericTypeParamDecl.TypeSequence = isTypeSequence;
+  Bits.GenericTypeParamDecl.IsOpaqueType = isOpaqueType;
+  assert(isOpaqueType || !opaqueTypeRepr);
+  if (isOpaqueType)
+    *getTrailingObjects<OpaqueReturnTypeRepr *>() = opaqueTypeRepr;
+
   auto &ctx = dc->getASTContext();
   RecursiveTypeProperties props = RecursiveTypeProperties::HasTypeParameter;
   if (this->isTypeSequence())
@@ -4120,6 +4125,21 @@ GenericTypeParamDecl::GenericTypeParamDecl(DeclContext *dc, Identifier name,
   setInterfaceType(MetatypeType::get(type, ctx));
 }
 
+GenericTypeParamDecl *
+GenericTypeParamDecl::create(
+    DeclContext *dc, Identifier name, SourceLoc nameLoc,
+    bool isTypeSequence, unsigned depth, unsigned index,
+    bool isOpaqueType, OpaqueReturnTypeRepr *opaqueTypeRepr) {
+  ASTContext &ctx = dc->getASTContext();
+  auto mem = ctx.Allocate(
+      totalSizeToAlloc<OpaqueReturnTypeRepr *>(isOpaqueType ? 1 : 0),
+      alignof(GenericTypeParamDecl));
+  return new (mem) GenericTypeParamDecl(
+      dc, name, nameLoc, isTypeSequence, depth, index, isOpaqueType,
+      opaqueTypeRepr);
+}
+
+
 SourceRange GenericTypeParamDecl::getSourceRange() const {
   SourceLoc endLoc = getNameLoc();
 
@@ -7857,15 +7877,15 @@ GenericTypeParamDecl *OpaqueTypeDecl::getExplicitGenericParam(
   return genericParamType->getDecl();
 }
 
-unsigned OpaqueTypeDecl::getAnonymousOpaqueParamOrdinal(
+Optional<unsigned> OpaqueTypeDecl::getAnonymousOpaqueParamOrdinal(
     OpaqueReturnTypeRepr *repr) const {
   assert(NamingDeclAndHasOpaqueReturnTypeRepr.getInt() &&
          "can't do opaque param lookup without underlying interface repr");
   auto opaqueReprs = getOpaqueReturnTypeReprs();
   auto found = std::find(opaqueReprs.begin(), opaqueReprs.end(), repr);
   if (found != opaqueReprs.end())
     return found - opaqueReprs.begin();
-  return -1;
+  return None;
 }
 
 Identifier OpaqueTypeDecl::getOpaqueReturnTypeIdentifier() const {

lib/AST/GenericParamList.cpp

@@ -73,9 +73,10 @@ GenericParamList::clone(DeclContext *dc) const {
   auto &ctx = dc->getASTContext();
   SmallVector<GenericTypeParamDecl *, 2> params;
   for (auto param : getParams()) {
-    auto *newParam = new (ctx) GenericTypeParamDecl(
+    auto *newParam = GenericTypeParamDecl::create(
         dc, param->getName(), SourceLoc(), param->isTypeSequence(),
-        GenericTypeParamDecl::InvalidDepth, param->getIndex());
+        GenericTypeParamDecl::InvalidDepth, param->getIndex(),
+        param->isOpaqueType(), param->getOpaqueTypeRepr());
     newParam->setImplicit(true);
     params.push_back(newParam);
   }