Implementing 0323 async main

CHANGELOG.md

@@ -29,6 +29,21 @@ CHANGELOG
 Swift 5.5
 ---------
 
+* [SE-0323][]:
+
+  The main function is executed with `MainActor` isolation applied, so functions
+  and variables with `MainActor` isolation may be called and modified
+  synchronously from the main function. If the main function is annotated with a
+  global actor explicitly, it must be the main actor or an error is emitted. If
+  no global actor annotation is present, the main function is implicitly run on
+  the main actor.
+
+  The main function is executed synchronously up to the first suspension point.
+  Any tasks enqueued by initializers in Objective-C or C++ will run after the
+  main function runs to the first suspension point. At the suspension point, the
+  main function suspends and the tasks are executed according to the Swift
+  concurrency mechanisms.
+
 * [SE-0313][]:
 
   Parameters of actor type can be declared as `isolated`, which means that they

include/swift/AST/DiagnosticsSema.def

@@ -4289,6 +4289,10 @@ NOTE(note_add_globalactor_to_function,none,
      "add '@%0' to make %1 %2 part of global actor %3", 
      (StringRef, DescriptiveDeclKind, DeclName, Type))
 FIXIT(insert_globalactor_attr, "@%0 ", (Type))
+
+ERROR(main_function_must_be_mainActor,none,
+      "main() must be '@MainActor'", ())
+
 ERROR(not_objc_function_async,none,
       "'async' %0 cannot be represented in Objective-C", (DescriptiveDeclKind))
 NOTE(not_objc_function_type_async,none,

include/swift/AST/FileUnit.h

@@ -273,7 +273,7 @@ class FileUnit : public DeclContext {
     return dyn_cast_or_null<ClassDecl>(getMainDecl());
   }
   bool hasMainDecl() const { return getMainDecl(); }
-  virtual Decl *getMainDecl() const { return nullptr; }
+  virtual ValueDecl *getMainDecl() const { return nullptr; }
   FuncDecl *getMainFunc() const {
     return dyn_cast_or_null<FuncDecl>(getMainDecl());
   }

include/swift/AST/SourceFile.h

@@ -99,7 +99,7 @@ class SourceFile final : public FileUnit {
 
   /// Either the class marked \@NS/UIApplicationMain or the synthesized FuncDecl
   /// that calls main on the type marked @main.
-  Decl *MainDecl = nullptr;
+  ValueDecl *MainDecl = nullptr;
 
   /// The source location of the main type.
   SourceLoc MainDeclDiagLoc;
@@ -488,7 +488,7 @@ class SourceFile final : public FileUnit {
     llvm_unreachable("bad SourceFileKind");
   }
 
-  Decl *getMainDecl() const override { return MainDecl; }
+  ValueDecl *getMainDecl() const override { return MainDecl; }
   SourceLoc getMainDeclDiagLoc() const {
     assert(hasMainDecl());
     return MainDeclDiagLoc;
@@ -502,7 +502,7 @@ class SourceFile final : public FileUnit {
   /// one.
   ///
   /// Should only be called during type-checking.
-  bool registerMainDecl(Decl *mainDecl, SourceLoc diagLoc);
+  bool registerMainDecl(ValueDecl *mainDecl, SourceLoc diagLoc);
 
   /// True if this source file has an application entry point.
   ///

include/swift/AST/TypeAlignments.h

@@ -38,6 +38,7 @@ namespace swift {
   class DifferentiableAttr;
   class Expr;
   class ExtensionDecl;
+  class FileUnit;
   class GenericEnvironment;
   class GenericParamList;
   class GenericTypeParamDecl;
@@ -123,6 +124,7 @@ LLVM_DECLARE_TYPE_ALIGNMENT(swift::BraceStmt, swift::StmtAlignInBits)
 
 LLVM_DECLARE_TYPE_ALIGNMENT(swift::ASTContext, swift::ASTContextAlignInBits);
 LLVM_DECLARE_TYPE_ALIGNMENT(swift::DeclContext, swift::DeclContextAlignInBits)
+LLVM_DECLARE_TYPE_ALIGNMENT(swift::FileUnit, swift::DeclContextAlignInBits)
 LLVM_DECLARE_TYPE_ALIGNMENT(swift::DifferentiableAttr, swift::PointerAlignInBits)
 LLVM_DECLARE_TYPE_ALIGNMENT(swift::Expr, swift::ExprAlignInBits)
 LLVM_DECLARE_TYPE_ALIGNMENT(swift::CaptureListExpr, swift::ExprAlignInBits)

include/swift/SIL/SILDeclRef.h

@@ -42,6 +42,7 @@ namespace swift {
   class AutoClosureExpr;
   class ASTContext;
   class ClassDecl;
+  class FileUnit;
   class SILFunctionType;
   enum IsSerialized_t : unsigned char;
   enum class SubclassScope : unsigned char;
@@ -83,7 +84,14 @@ enum ForDefinition_t : bool {
 /// declaration, such as uncurry levels of a function, the allocating and
 /// initializing entry points of a constructor, etc.
 struct SILDeclRef {
-  using Loc = llvm::PointerUnion<ValueDecl *, AbstractClosureExpr *>;
+  /// The type of AST node location being stored.
+  enum LocKind {
+    Decl,
+    Closure,
+    File
+  };
+  using Loc = llvm::PointerUnion<ValueDecl *, AbstractClosureExpr *,
+                                 FileUnit *>;
 
   /// Represents the "kind" of the SILDeclRef. For some Swift decls there
   /// are multiple SIL entry points, and the kind is used to distinguish them.
@@ -144,9 +152,16 @@ struct SILDeclRef {
     /// References the function used to initialize a property wrapper storage
     /// instance from a projected value.
     PropertyWrapperInitFromProjectedValue,
+
+    /// The main entry-point function. This may reference a SourceFile for a
+    /// top-level main, or a decl for e.g an @main decl.
+    EntryPoint,
+
+    /// The asynchronous main entry-point function.
+    AsyncEntryPoint,
   };
-  
-  /// The ValueDecl or AbstractClosureExpr represented by this SILDeclRef.
+
+  /// The AST node represented by this SILDeclRef.
   Loc loc;
   /// The Kind of this SILDeclRef.
   Kind kind : 4;
@@ -159,6 +174,17 @@ struct SILDeclRef {
                const GenericSignatureImpl *>
       pointer;
 
+  /// Returns the type of AST node location being stored by the SILDeclRef.
+  LocKind getLocKind() const {
+    if (loc.is<ValueDecl *>())
+      return LocKind::Decl;
+    if (loc.is<AbstractClosureExpr *>())
+      return LocKind::Closure;
+    if (loc.is<FileUnit *>())
+      return LocKind::File;
+    llvm_unreachable("Unhandled location kind!");
+  }
+
   /// The derivative function identifier.
   AutoDiffDerivativeFunctionIdentifier * getDerivativeFunctionIdentifier() const {
     if (!pointer.is<AutoDiffDerivativeFunctionIdentifier *>())
@@ -201,6 +227,15 @@ struct SILDeclRef {
   /// Produce a SIL constant for a default argument generator.
   static SILDeclRef getDefaultArgGenerator(Loc loc, unsigned defaultArgIndex);
 
+  /// Produces a SILDeclRef for a synthetic main entry-point such as @main.
+  static SILDeclRef getMainDeclEntryPoint(ValueDecl *decl);
+
+  /// Produces a SILDeclRef for the synthesized async main entry-point
+  static SILDeclRef getAsyncMainDeclEntryPoint(ValueDecl *decl);
+
+  /// Produces a SILDeclRef for the entry-point of a main FileUnit.
+  static SILDeclRef getMainFileEntryPoint(FileUnit *file);
+
   bool isNull() const { return loc.isNull(); }
   explicit operator bool() const { return !isNull(); }
 
@@ -217,7 +252,13 @@ struct SILDeclRef {
   AutoClosureExpr *getAutoClosureExpr() const;
   FuncDecl *getFuncDecl() const;
   AbstractFunctionDecl *getAbstractFunctionDecl() const;
-
+  FileUnit *getFileUnit() const {
+    return loc.get<FileUnit *>();
+  }
+
+  /// Retrieves the ASTContext from the underlying AST node being stored.
+  ASTContext &getASTContext() const;
+
   llvm::Optional<AnyFunctionRef> getAnyFunctionRef() const;
 
   SILLocation getAsRegularLocation() const;

include/swift/Serialization/SerializedModuleLoader.h

@@ -433,7 +433,7 @@ class SerializedASTFile final : public LoadedFile {
 
   virtual StringRef getModuleDefiningPath() const override;
 
-  Decl *getMainDecl() const override;
+  ValueDecl *getMainDecl() const override;
 
   bool hasEntryPoint() const override;
 

lib/AST/Module.cpp

@@ -1587,7 +1587,7 @@ bool ModuleDecl::isBuiltinModule() const {
   return this == getASTContext().TheBuiltinModule;
 }
 
-bool SourceFile::registerMainDecl(Decl *mainDecl, SourceLoc diagLoc) {
+bool SourceFile::registerMainDecl(ValueDecl *mainDecl, SourceLoc diagLoc) {
   assert(mainDecl);
   if (mainDecl == MainDecl)
     return false;

lib/IRGen/GenObjC.cpp

@@ -473,6 +473,8 @@ namespace {
       case SILDeclRef::Kind::GlobalAccessor:
       case SILDeclRef::Kind::PropertyWrapperBackingInitializer:
       case SILDeclRef::Kind::PropertyWrapperInitFromProjectedValue:
+      case SILDeclRef::Kind::EntryPoint:
+      case SILDeclRef::Kind::AsyncEntryPoint:
         llvm_unreachable("Method does not have a selector");
 
       case SILDeclRef::Kind::Destroyer: