[WIP] @_inheritActorContext(always)

Runtimes/Core/Concurrency/CMakeLists.txt

@@ -1,7 +1,7 @@
 add_subdirectory(InternalShims)
 
 gyb_expand(TaskGroup+addTask.swift.gyb TaskGroup+addTask.swift)
-gyb_expand(Task+startSynchronously.swift.gyb Task+startSynchronously.swift)
+gyb_expand(Task+immediate.swift.gyb Task+immediate.swift)
 
 add_library(swift_Concurrency
   Actor.cpp
@@ -97,7 +97,7 @@ add_library(swift_Concurrency
   TaskSleep.swift
   TaskSleepDuration.swift
   "${CMAKE_CURRENT_BINARY_DIR}/TaskGroup+addTask.swift"
-  "${CMAKE_CURRENT_BINARY_DIR}/Task+startSynchronously.swift")
+  "${CMAKE_CURRENT_BINARY_DIR}/Task+immediate.swift")
 
 include(${SwiftCore_CONCURRENCY_GLOBAL_EXECUTOR}.cmake)
 target_compile_definitions(swift_Concurrency PRIVATE

docs/ReferenceGuides/UnderscoredAttributes.md

@@ -600,6 +600,43 @@ inherit the actor context (i.e. what actor it should be run on) based on the
 declaration site of the closure rather than be non-Sendable. This does not do
 anything if the closure is synchronous.
 
+This works with global actors as expected:
+
+```swift 
+@MainActor
+func test() {
+  Task { /* main actor isolated */ }
+}
+```
+
+However, for the inference to work with instance actors (i.e. `isolated` parameters),
+the closure must capture the isolated parameter explicitly:
+
+```swift 
+func test(actor: isolated (any Actor)) {
+  Task { /* non isolated */ } // !!!
+}
+
+func test(actor: isolated (any Actor)) {
+  Task { // @_inheritActorContext
+    _ = actor // 'actor'-isolated 
+  }
+}
+```
+
+The attribute takes an optional modifier '`always`', which changes this behavior 
+and *always* captures the enclosing isolated context, rather than forcing developers
+to perform the explicit capture themselfes:
+
+```swift
+func test(actor: isolated (any Actor)) {
+  Task.immediate { // @_inheritActorContext(always)
+    // 'actor'-isolated!
+    // (without having to capture 'actor explicitly')
+  }
+}
+```
+
 DISCUSSION: The reason why this does nothing when the closure is synchronous is
 since it does not have the ability to hop to the appropriate executor before it
 is run, so we may create concurrency errors.

include/swift/ABI/Executor.h

@@ -77,7 +77,7 @@ class SerialExecutorRef {
     /// Executor that may need to participate in complex "same context" checks,
     /// by invoking `isSameExclusiveExecutionContext` when comparing execution contexts.
     ComplexEquality = 0b01,
-    /// Mark this executor as the one used by `Task.startSynchronously`,
+    /// Mark this executor as the one used by `Task.immediate`,
     /// It cannot participate in switching.
     // TODO: Perhaps make this a generic "cannot switch" rather than start synchronously specific.
     StartSynchronously = 0b10,

include/swift/AST/Attr.h

@@ -17,6 +17,7 @@
 #ifndef SWIFT_ATTR_H
 #define SWIFT_ATTR_H
 
+#include "Attr.h"
 #include "swift/AST/ASTAllocated.h"
 #include "swift/AST/AttrKind.h"
 #include "swift/AST/AutoDiff.h"
@@ -42,10 +43,10 @@
 #include "swift/Basic/SourceLoc.h"
 #include "swift/Basic/UUID.h"
 #include "swift/Basic/Version.h"
-#include "llvm/ADT/bit.h"
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/bit.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TrailingObjects.h"
@@ -230,6 +231,10 @@ class DeclAttribute : public AttributeBase {
       Modifier : NumNonIsolatedModifierBits
     );
 
+    SWIFT_INLINE_BITFIELD(InheritActorContextAttr, DeclAttribute, NumInheritActorContextKindBits,
+      Modifier : NumInheritActorContextKindBits
+    );
+
     SWIFT_INLINE_BITFIELD_FULL(AllowFeatureSuppressionAttr, DeclAttribute, 1+31,
       : NumPadBits,
       Inverted : 1,
@@ -3011,6 +3016,51 @@ class NonisolatedAttr final : public DeclAttribute {
   }
 };
 
+/// Represents @_inheritActorContext modifier.
+class InheritActorContextAttr final : public DeclAttribute {
+public:
+  InheritActorContextAttr(SourceLoc atLoc, SourceRange range,
+                          InheritActorContextModifier modifier, bool implicit)
+      : DeclAttribute(DeclAttrKind::InheritActorContext, atLoc, range, implicit) {
+    Bits.InheritActorContextAttr.Modifier = static_cast<unsigned>(modifier);
+    assert((getModifier() == modifier) && "not enough bits for modifier");
+  }
+
+  InheritActorContextModifier getModifier() const {
+    return static_cast<InheritActorContextModifier>(Bits.InheritActorContextAttr.Modifier);
+  }
+
+  bool isAlways() const { return getModifier() == InheritActorContextModifier::Always; }
+
+  static InheritActorContextAttr *
+  createImplicit(ASTContext &ctx,
+                 InheritActorContextModifier modifier = InheritActorContextModifier::Default) {
+    return new (ctx) InheritActorContextAttr(/*atLoc*/ {}, /*range*/ {}, modifier,
+                                             /*implicit=*/true);
+  }
+
+  static bool classof(const DeclAttribute *DA) {
+    return DA->getKind() == DeclAttrKind::InheritActorContext;
+  }
+
+  /// Create a copy of this attribute.
+  InheritActorContextAttr *clone(ASTContext &ctx) const {
+    return new (ctx) InheritActorContextAttr(AtLoc, Range, getModifier(), isImplicit());
+  }
+
+  bool isEquivalent(const InheritActorContextAttr *other, Decl *attachedTo) const {
+    return getModifier() == other->getModifier();
+  }
+
+  const char *getModifierName() const {
+    return getModifierName(getModifier());
+  }
+  static const char *getModifierName(InheritActorContextModifier modifier);
+
+  void printImpl(ASTPrinter &printer, const PrintOptions &options) const;
+
+};
+
 /// A macro role attribute, spelled with either @attached or @freestanding,
 /// which declares one of the roles that a given macro can inhabit.
 class MacroRoleAttr final

include/swift/AST/AttrKind.h

@@ -142,6 +142,20 @@ enum : unsigned {
       static_cast<unsigned>(NonIsolatedModifier::Last_NonIsolatedModifier))
 };
 
+enum class InheritActorContextModifier: uint8_t {
+  /// Only inherit the actor execution context if the isolated parameter was
+  /// captured by the closure.
+  Default,
+
+  /// Always inherit the actor context, even when the isolated parameter
+  /// is not closed over explicitly.
+  Always,
+  Last_InheritActorContextKind = Always
+};
+
+enum : unsigned { NumInheritActorContextKindBits =
+  countBitsUsed(static_cast<unsigned>(InheritActorContextModifier::Last_InheritActorContextKind)) };
+
 enum class DeclAttrKind : unsigned {
 #define DECL_ATTR(_, CLASS, ...) CLASS,
 #define LAST_DECL_ATTR(CLASS) Last_DeclAttr = CLASS,

include/swift/AST/DeclAttr.def

@@ -620,9 +620,10 @@ SIMPLE_DECL_ATTR(_implicitSelfCapture, ImplicitSelfCapture,
   UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIBreakingToRemove | ForbiddenInABIAttr,
   115)
 
-SIMPLE_DECL_ATTR(_inheritActorContext, InheritActorContext,
+DECL_ATTR(_inheritActorContext, InheritActorContext,
   OnParam,
-  UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIBreakingToAdd | APIBreakingToRemove | ForbiddenInABIAttr,
+  // since the _inheritActorContext(always) forces an actor capture, it changes ABI of the closure this applies to
+  UserInaccessible | ABIBreakingToAdd | ABIBreakingToRemove | APIBreakingToAdd | APIBreakingToRemove | UnconstrainedInABIAttr,
   116)
 
 SIMPLE_DECL_ATTR(_eagerMove, EagerMove,

include/swift/AST/Expr.h

@@ -267,7 +267,7 @@ class alignas(8) Expr : public ASTAllocated<Expr> {
     Kind : 2
   );
 
-  SWIFT_INLINE_BITFIELD(ClosureExpr, AbstractClosureExpr, 1+1+1+1+1+1+1+1,
+  SWIFT_INLINE_BITFIELD(ClosureExpr, AbstractClosureExpr, 1+1+1+1+1+1+1+1+1,
     /// True if closure parameters were synthesized from anonymous closure
     /// variables.
     HasAnonymousClosureVars : 1,
@@ -279,6 +279,7 @@ class alignas(8) Expr : public ASTAllocated<Expr> {
     /// True if this @Sendable async closure parameter should implicitly
     /// inherit the actor context from where it was formed.
     InheritActorContext : 1,
+    InheritActorContextAlways : 1,
 
     /// True if this closure's actor isolation behavior was determined by an
     /// \c \@preconcurrency declaration.
@@ -4366,8 +4367,23 @@ class ClosureExpr : public AbstractClosureExpr {
     return Bits.ClosureExpr.InheritActorContext;
   }
 
-  void setInheritsActorContext(bool value = true) {
-    Bits.ClosureExpr.InheritActorContext = value;
+  void setInheritsActorContext(InheritActorContextModifier modifier = InheritActorContextModifier::Default) { // TODO: change into enum
+    switch (modifier) {
+      case InheritActorContextModifier::Default: {
+        Bits.ClosureExpr.InheritActorContext = true;
+        Bits.ClosureExpr.InheritActorContextAlways = true;
+        break;
+      }
+      case InheritActorContextModifier::Always: {
+        Bits.ClosureExpr.InheritActorContext = true;
+        Bits.ClosureExpr.InheritActorContextAlways = true;
+        break;
+      }
+    }
+  }
+
+  bool inheritsActorContextAlways() const {
+    return Bits.ClosureExpr.InheritActorContextAlways;
   }
 
   /// Whether the closure's concurrency behavior was determined by an

include/swift/AST/KnownIdentifiers.def

@@ -326,6 +326,7 @@ IDENTIFIER_WITH_NAME(builderSelf, "$builderSelf")
 
 // Attribute options
 IDENTIFIER_(_always)
+IDENTIFIER(always)
 IDENTIFIER_(assumed)
 IDENTIFIER(checked)
 IDENTIFIER(never)

include/swift/AST/Types.h

@@ -4049,6 +4049,7 @@ struct ParameterListInfo {
   SmallBitVector propertyWrappers;
   SmallBitVector implicitSelfCapture;
   SmallBitVector inheritActorContext;
+  SmallBitVector inheritActorContextAlways;
   SmallBitVector variadicGenerics;
   SmallBitVector sendingParameters;
 
@@ -4076,6 +4077,7 @@ struct ParameterListInfo {
   /// Whether the given parameter is a closure that should inherit the
   /// actor context from the context in which it was created.
   bool inheritsActorContext(unsigned paramIdx) const;
+  bool inheritsActorContextAlways(unsigned paramIdx) const;
 
   bool isVariadicGenericParameter(unsigned paramIdx) const;
 

include/swift/Basic/Features.def

@@ -191,6 +191,7 @@ BASELINE_LANGUAGE_FEATURE(BuiltinContinuation, 0, "Continuation builtins")
 BASELINE_LANGUAGE_FEATURE(BuiltinHopToActor, 0, "Builtin.HopToActor")
 BASELINE_LANGUAGE_FEATURE(BuiltinTaskGroupWithArgument, 0, "TaskGroup builtins")
 BASELINE_LANGUAGE_FEATURE(InheritActorContext, 0, "@_inheritActorContext attribute")
+BASELINE_LANGUAGE_FEATURE(InheritActorContextAlways, 0, "@_inheritActorContext(always) attribute")
 BASELINE_LANGUAGE_FEATURE(ImplicitSelfCapture, 0, "@_implicitSelfCapture attribute")
 BASELINE_LANGUAGE_FEATURE(BuiltinBuildTaskExecutorRef, 0, "TaskExecutor-building builtins")
 BASELINE_LANGUAGE_FEATURE(BuiltinBuildExecutor, 0, "Executor-building builtins")

include/swift/Parse/IDEInspectionCallbacks.h

@@ -39,7 +39,8 @@ enum class ParameterizedDeclAttributeKind {
   Available,
   FreestandingMacro,
   AttachedMacro,
-  StorageRestrictions
+  StorageRestrictions,
+  InheritActorContext
 };
 
 /// A bit of a hack. When completing inside the '@storageRestrictions'

lib/AST/ASTDumper.cpp

@@ -4110,8 +4110,14 @@ class PrintExpr : public ExprVisitor<PrintExpr, void, Label>,
               ClosureModifierColor);
     printFlag(E->allowsImplicitSelfCapture(), "implicit_self",
               ClosureModifierColor);
-    printFlag(E->inheritsActorContext(), "inherits_actor_context",
+
+    if (E->inheritsActorContextAlways()) {
+      printFlag(E->inheritsActorContextAlways(), "inherits_actor_context(always)",
+                ClosureModifierColor);
+    } else {
+      printFlag(E->inheritsActorContext(), "inherits_actor_context",
               ClosureModifierColor);
+    }
 
     if (E->getParameters()) {
       printRec(E->getParameters(), Label::optional("params"),

lib/AST/Attr.cpp

@@ -15,6 +15,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "swift/AST/Attr.h"
+#include "swift/AST/ASTBridging.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/ASTPrinter.h"
 #include "swift/AST/AvailabilityDomain.h"
@@ -34,6 +35,7 @@
 #include "swift/Basic/Defer.h"
 #include "swift/Basic/QuotedString.h"
 #include "swift/Strings.h"
+
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringSwitch.h"
@@ -304,6 +306,33 @@ void IsolatedTypeAttr::printImpl(ASTPrinter &printer,
   printer.printStructurePost(PrintStructureKind::BuiltinAttribute);
 }
 
+const char *InheritActorContextAttr::getModifierName(
+  InheritActorContextModifier modifier) {
+  switch (modifier) {
+  case InheritActorContextModifier::Default: return "";
+  case InheritActorContextModifier::Always: return "always";
+  }
+  llvm_unreachable("bad kind");
+}
+
+
+void InheritActorContextAttr::printImpl(ASTPrinter &printer,
+  const PrintOptions &options) const {
+  printer.callPrintStructurePre(PrintStructureKind::BuiltinAttribute);
+  printer.printAttrName("@_inheritActorContext");
+
+  switch (getModifier()) {
+  case InheritActorContextModifier::Default:
+    break;
+  case InheritActorContextModifier::Always: {
+    printer << "(" << getModifierName() << ")";
+    break;
+  }
+  }
+
+  printer.printStructurePost(PrintStructureKind::BuiltinAttribute);
+}
+
 /// Given a name like "inline", return the decl attribute ID that corresponds
 /// to it.  Note that this is a many-to-one mapping, and that the identifier
 /// passed in may only be the first portion of the attribute (e.g. in the case
@@ -1531,6 +1560,18 @@ bool DeclAttribute::printImpl(ASTPrinter &Printer, const PrintOptions &Options,
     break;
   }
 
+  case DeclAttrKind::InheritActorContext: {
+    Printer.printAttrName("@_inheritActorContext");
+    switch (cast<InheritActorContextAttr>(this)->getModifier()) {
+    case InheritActorContextModifier::Default:
+      break;
+    case InheritActorContextModifier::Always:
+      Printer << "(always)";
+      break;
+    }
+    break;
+  }
+
   case DeclAttrKind::MacroRole: {
     auto Attr = cast<MacroRoleAttr>(this);
 
@@ -1915,6 +1956,13 @@ StringRef DeclAttribute::getAttrName() const {
     case NonIsolatedModifier::NonSending:
       return "nonisolated(nonsending)";
     }
+  case DeclAttrKind::InheritActorContext:
+    switch (cast<InheritActorContextAttr>(this)->getModifier()) {
+    case InheritActorContextModifier::Default:
+      return "@_inheritActorContext";
+    case InheritActorContextModifier::Always:
+      return "@_inheritActorContext(always)";
+    }
   case DeclAttrKind::MacroRole:
     switch (cast<MacroRoleAttr>(this)->getMacroSyntax()) {
     case MacroSyntax::Freestanding: