[sending] Begin parsing 'sending' while still accepting 'transferring'.

A few things:

1. Internally except for in the parser and the clang importer, we only represent
'sending'. This means that it will be easy to remove 'transferring' once enough
time has passed.

2. I included a warning that suggested to the user to change 'transferring' ->
'sending'.

3. I duplicated the parsing diagnostics for 'sending' so both will still get
different sets of diagnostics for parsing issues... but anywhere below parsing,
I have just changed 'transferring' to 'sending' since transferring isn't
represented at those lower levels.

4. Since SendingArgsAndResults is always enabled when TransferringArgsAndResults
is enabled (NOTE not vis-a-versa), we know that we can always parse sending. So
we import "transferring" as "sending". This means that even if one marks a
function with "transferring", the compiler will guard it behind a
SendingArgsAndResults -D flag and in the imported header print out sending.

rdar://128216574

Author: gottesmm

include/swift/AST/ASTBridging.h

@@ -1552,6 +1552,7 @@ enum ENUM_EXTENSIBILITY_ATTR(open) BridgedAttributedTypeSpecifier : size_t {
   BridgedAttributedTypeSpecifierIsolated,
   BridgedAttributedTypeSpecifierResultDependsOn,
   BridgedAttributedTypeSpecifierTransferring,
+  BridgedAttributedTypeSpecifierSending,
 };
 
 SWIFT_NAME("BridgedUnqualifiedIdentTypeRepr.createParsed(_:loc:name:)")

include/swift/AST/Builtins.def

@@ -868,7 +868,7 @@ BUILTIN_MISC_OPERATION_WITH_SILGEN(GetCurrentAsyncTask, "getCurrentAsyncTask", "
 BUILTIN_MISC_OPERATION_WITH_SILGEN(CancelAsyncTask, "cancelAsyncTask", "", Special)
 
 /// startAsyncLet()<T>: (
-///     __owned @escaping () async throws -> transferring T
+///     __owned @escaping () async throws -> sending T
 /// ) -> Builtin.RawPointer
 ///
 /// DEPRECATED. startAsyncLetWithLocalBuffer is used instead.
@@ -878,7 +878,7 @@ BUILTIN_MISC_OPERATION_WITH_SILGEN(CancelAsyncTask, "cancelAsyncTask", "", Speci
 BUILTIN_MISC_OPERATION(StartAsyncLet, "startAsyncLet", "", Special)
 
 /// startAsyncLetWithLocalBuffer()<T>: (
-///     __owned @escaping () async throws -> transferring T,
+///     __owned @escaping () async throws -> sending T,
 ///     _ resultBuf: Builtin.RawPointer
 /// ) -> Builtin.RawPointer
 ///

include/swift/AST/DiagnosticsParse.def

@@ -2200,6 +2200,16 @@ ERROR(transferring_after_parameter_specifier,none,
       "'transferring' must be placed before specifier '%0'", (StringRef))
 ERROR(transferring_repeated,none,
       "parameter may have at most one 'transferring' specifier", ())
+ERROR(sending_before_parameter_specifier,none,
+      "'sending' must be placed after specifier '%0'", (StringRef))
+ERROR(sending_repeated,none,
+      "parameter may have at most one 'sending' specifier", ())
+ERROR(sending_and_transferring_used_together,none,
+      "'transferring' and 'sending' may not be used together", ())
+WARNING(transferring_is_now_sendable,none,
+        "'transferring' has been renamed to 'sending' and the 'transferring' spelling will be removed shortly",
+        ())
+
 
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

include/swift/AST/DiagnosticsSema.def

@@ -7972,17 +7972,23 @@ ERROR(lifetime_dependence_cannot_infer_ambiguous_candidate, none,
        "Escapable",
        ())
 
- //===----------------------------------------------------------------------===//
- //                             MARK: Transferring
- //===----------------------------------------------------------------------===//
-
- ERROR(transferring_unsupported_param_specifier, none,
-       "'%0' cannot be applied to a 'transferring' parameter", (StringRef))
+//===----------------------------------------------------------------------===//
+//                             MARK: Transferring
+//===----------------------------------------------------------------------===//
 
- ERROR(transferring_only_on_parameters_and_results, none,
-       "'transferring' may only be used on parameters and results", ())
- ERROR(transferring_cannot_be_applied_to_tuple_elt, none,
-       "'transferring' cannot be applied to tuple elements", ())
+ERROR(transferring_unsupported_param_specifier, none,
+      "'%0' cannot be applied to a 'transferring' parameter", (StringRef))
+
+ERROR(transferring_only_on_parameters_and_results, none,
+      "'transferring' may only be used on parameters and results", ())
+ERROR(transferring_cannot_be_applied_to_tuple_elt, none,
+      "'transferring' cannot be applied to tuple elements", ())
+ERROR(sending_unsupported_param_specifier, none,
+      "'%0' cannot be applied to a 'sending' parameter", (StringRef))
+ERROR(sending_only_on_parameters_and_results, none,
+      "'sending' may only be used on parameters and results", ())
+ERROR(sending_cannot_be_applied_to_tuple_elt, none,
+      "'sending' cannot be applied to tuple elements", ())
 
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

include/swift/AST/PrintOptions.h

@@ -382,8 +382,8 @@ struct PrintOptions {
   /// Suppress 'isolated' and '#isolation' on isolated parameters with optional type.
   bool SuppressOptionalIsolatedParams = false;
 
-  /// Suppress 'transferring' on arguments and results.
-  bool SuppressTransferringArgsAndResults = false;
+  /// Suppress 'sending' on arguments and results.
+  bool SuppressSendingArgsAndResults = false;
 
   /// Suppress Noncopyable generics.
   bool SuppressNoncopyableGenerics = false;

include/swift/AST/TypeRepr.h

@@ -1116,7 +1116,8 @@ class SpecifierTypeRepr : public TypeRepr {
            T->getKind() == TypeReprKind::CompileTimeConst ||
            T->getKind() == TypeReprKind::ResultDependsOn ||
            T->getKind() == TypeReprKind::LifetimeDependentReturn ||
-           T->getKind() == TypeReprKind::Transferring;
+           T->getKind() == TypeReprKind::Transferring ||
+           T->getKind() == TypeReprKind::Sending;
   }
   static bool classof(const SpecifierTypeRepr *T) { return true; }
 
@@ -1217,6 +1218,21 @@ class TransferringTypeRepr : public SpecifierTypeRepr {
   static bool classof(const TransferringTypeRepr *T) { return true; }
 };
 
+/// A sending type.
+/// \code
+///   x : sending Int
+/// \endcode
+class SendingTypeRepr : public SpecifierTypeRepr {
+public:
+  SendingTypeRepr(TypeRepr *Base, SourceLoc Loc)
+      : SpecifierTypeRepr(TypeReprKind::Sending, Base, Loc) {}
+
+  static bool classof(const TypeRepr *T) {
+    return T->getKind() == TypeReprKind::Sending;
+  }
+  static bool classof(const SendingTypeRepr *T) { return true; }
+};
+
 /// A TypeRepr for a known, fixed type.
 ///
 /// Fixed type representations should be used sparingly, in places
@@ -1618,6 +1634,7 @@ inline bool TypeRepr::isSimple() const {
   case TypeReprKind::SILBox:
   case TypeReprKind::Isolated:
   case TypeReprKind::Transferring:
+  case TypeReprKind::Sending:
   case TypeReprKind::Placeholder:
   case TypeReprKind::CompileTimeConst:
   case TypeReprKind::ResultDependsOn:

include/swift/AST/TypeReprNodes.def

@@ -72,6 +72,7 @@ ABSTRACT_TYPEREPR(Specifier, TypeRepr)
   SPECIFIER_TYPEREPR(CompileTimeConst, SpecifierTypeRepr)
   SPECIFIER_TYPEREPR(ResultDependsOn, SpecifierTypeRepr)
   SPECIFIER_TYPEREPR(Transferring, SpecifierTypeRepr)
+  SPECIFIER_TYPEREPR(Sending, SpecifierTypeRepr)
 TYPEREPR(Fixed, TypeRepr)
 TYPEREPR(SILBox, TypeRepr)
 TYPEREPR(Self, TypeRepr)

include/swift/Basic/Features.def

@@ -353,7 +353,14 @@ EXPERIMENTAL_FEATURE(FixedArrays, true)
 EXPERIMENTAL_FEATURE(GroupActorErrors, true)
 
 // Allow for the 'transferring' keyword to be applied to arguments and results.
-SUPPRESSIBLE_EXPERIMENTAL_FEATURE(TransferringArgsAndResults, true)
+//
+// Enables SendingArgsAndResults as well. After parsing, we just represent this
+// as 'sendable' implying that since both are always enabled together, this
+// doesn't need to be suppressed.
+EXPERIMENTAL_FEATURE(TransferringArgsAndResults, true)
+
+// Allow for the 'sending' keyword to be applied to arguments and results.
+SUPPRESSIBLE_EXPERIMENTAL_FEATURE(SendingArgsAndResults, true)
 
 // Enable explicit isolation of closures.
 EXPERIMENTAL_FEATURE(ClosureIsolation, true)

include/swift/Parse/Parser.h

@@ -1206,6 +1206,9 @@ class Parser {
     if (Context.LangOpts.hasFeature(Feature::TransferringArgsAndResults) &&
         Tok.isContextualKeyword("transferring"))
       return true;
+    if (Context.LangOpts.hasFeature(Feature::SendingArgsAndResults) &&
+        Tok.isContextualKeyword("sending"))
+      return true;
     if (Context.LangOpts.hasFeature(Feature::NonescapableTypes) &&
         (Tok.isContextualKeyword("_resultDependsOn") ||
          isLifetimeDependenceToken()))
@@ -1256,6 +1259,7 @@ class Parser {
     SourceLoc ConstLoc;
     SourceLoc ResultDependsOnLoc;
     SourceLoc TransferringLoc;
+    SourceLoc SendingLoc;
     SmallVector<TypeOrCustomAttr> Attributes;
     SmallVector<LifetimeDependenceSpecifier> lifetimeDependenceSpecifiers;
 
@@ -1573,6 +1577,9 @@ class Parser {
     /// The location of the 'transferring' keyword if present.
     SourceLoc TransferringLoc;
 
+    /// The location of the 'sending' keyword if present.
+    SourceLoc SendingLoc;
+
     /// The type following the ':'.
     TypeRepr *Type = nullptr;
 

lib/AST/ASTBridging.cpp

@@ -878,6 +878,8 @@ BridgedParamDecl BridgedParamDecl_createParsed(
           paramDecl->setCompileTimeConst(true);
         else if (isa<TransferringTypeRepr>(STR))
           paramDecl->setSending(true);
+        else if (isa<SendingTypeRepr>(STR))
+          paramDecl->setSending(true);
 
         unwrappedType = STR->getBase();
         continue;
@@ -2225,6 +2227,9 @@ BridgedSpecifierTypeRepr BridgedSpecifierTypeRepr_createParsed(
   case BridgedAttributedTypeSpecifierTransferring: {
     return new (context) TransferringTypeRepr(baseType, loc);
   }
+  case BridgedAttributedTypeSpecifierSending: {
+    return new (context) SendingTypeRepr(baseType, loc);
+  }
   case BridgedAttributedTypeSpecifierConst: {
     return new (context) CompileTimeConstTypeRepr(baseType, loc);
   }