[Concurrency] Remove -executor-factory option and replace with magic type.

We decided that using a magic typealias to set the executor factory was better
than using a compiler option. Remove the `-executor-factory` option, and replace
by looking up the `DefaultExecutorFactory` type, first in the main module, and
then if that fails in Concurrency.

rdar://149058236

Author: al45tair

Diff for: include/swift/AST/DiagnosticsSIL.def

@@ -1137,12 +1137,9 @@ NOTE(rbi_add_generic_parameter_sendable_conformance,none,
 
 // Concurrency related diagnostics
 ERROR(cannot_find_executor_factory_type, none,
-      "the specified executor factory '%0' could not be found", (StringRef))
+      "the DefaultExecutorFactory type could not be found", ())
 ERROR(executor_factory_must_conform, none,
-      "the executor factory '%0' does not conform to 'ExecutorFactory'",
-      (StringRef))
-ERROR(executor_factory_not_supported, none,
-      "deployment target too low for executor factory specification", ())
+      "the DefaultExecutorFactory does not conform to 'ExecutorFactory'", ())
 
 //===----------------------------------------------------------------------===//
 //                           MARK: Misc Diagnostics

Diff for: include/swift/Basic/LangOptions.h

@@ -409,10 +409,6 @@ namespace swift {
     /// Specifies how strict concurrency checking will be.
     StrictConcurrency StrictConcurrencyLevel = StrictConcurrency::Minimal;
 
-    /// Specifies the name of the executor factory to use to create the
-    /// default executors for Swift Concurrency.
-    std::optional<std::string> ExecutorFactory;
-
     /// Enable experimental concurrency model.
     bool EnableExperimentalConcurrency = false;
 

Diff for: include/swift/Option/Options.td

@@ -998,16 +998,6 @@ def default_isolation_EQ :  Joined<["-"], "default-isolation=">,
   Flags<[FrontendOption]>,
   Alias<default_isolation>;
 
-def executor_factory : JoinedOrSeparate<["-"], "executor-factory">,
-  Flags<[FrontendOption]>,
-  HelpText<"Specify the factory to use to create the default executors for "
-           "Swift Concurrency.  This must be a type conforming to the "
-           "'ExecutorFactory' protocol.">,
-  MetaVarName<"<factory-type>">;
-def executor_factory_EQ : Joined<["-"], "executor-factory=">,
-  Flags<[FrontendOption]>,
-  Alias<executor_factory>;
-
 def enable_experimental_feature :
   Separate<["-"], "enable-experimental-feature">,
   Flags<[FrontendOption, ModuleInterfaceOption]>,

Diff for: lib/Driver/ToolChains.cpp

@@ -379,10 +379,6 @@ void ToolChain::addCommonFrontendArgs(const OutputInfo &OI,
     arguments.push_back(inputArgs.MakeArgString(globalRemapping));
   }
 
-  if (inputArgs.hasArg(options::OPT_executor_factory)) {
-    inputArgs.AddLastArg(arguments, options::OPT_executor_factory);
-  }
-
   // Pass through the values passed to -Xfrontend.
   inputArgs.AddAllArgValues(arguments, options::OPT_Xfrontend);
 

Diff for: lib/Frontend/CompilerInvocation.cpp

@@ -1364,12 +1364,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.enableFeature(Feature::RegionBasedIsolation);
   }
 
-  // Get the executor factory name
-  if (const Arg *A = Args.getLastArg(OPT_executor_factory)) {
-    printf("Got executor-factory option\n");
-    Opts.ExecutorFactory = A->getValue();
-  }
-
   Opts.WarnImplicitOverrides =
     Args.hasArg(OPT_warn_implicit_overrides);
 

Diff for: lib/SILGen/SILGen.cpp

@@ -514,25 +514,14 @@ FuncDecl *SILGenModule::getExit() {
 Type SILGenModule::getConfiguredExecutorFactory() {
   auto &ctx = getASTContext();
 
-  ModuleDecl *module;
+  // Look in the main module for a typealias
+  Type factory = ctx.getNamedSwiftType(ctx.MainModule, "DefaultExecutorFactory");
 
-  // Parse the executor factory name
-  StringRef qualifiedName = *ctx.LangOpts.ExecutorFactory;
-  StringRef typeName;
+  // If we don't find it, fall back to _Concurrency.PlatformExecutorFactory
+  if (!factory)
+    factory = getDefaultExecutorFactory();
 
-  auto parts = qualifiedName.split('.');
-
-  if (parts.second.empty()) {
-    // This was an unqualified name; assume it's relative to the main module
-    module = ctx.MainModule;
-    typeName = qualifiedName;
-  } else {
-    Identifier moduleName = ctx.getIdentifier(parts.first);
-    module = ctx.getModuleByIdentifier(moduleName);
-    typeName = parts.second;
-  }
-
-  return ctx.getNamedSwiftType(module, typeName);
+  return factory;
 }
 
 Type SILGenModule::getDefaultExecutorFactory() {

Diff for: lib/SILGen/SILGenFunction.cpp

@@ -1424,51 +1424,44 @@ void SILGenFunction::emitAsyncMainThreadStart(SILDeclRef entryPoint) {
 
   B.setInsertionPoint(entryBlock);
 
-  // If we're using a new enough deployment target, call swift_createExecutors()
-  if (ctx.LangOpts.ExecutorFactory) {
-    if (!isCreateExecutorsFunctionAvailable(SGM)) {
-      ctx.Diags.diagnose(SourceLoc(), diag::executor_factory_not_supported);
-    } else {
-      CanType factoryTy = SGM.getConfiguredExecutorFactory()->getCanonicalType();
+  // If we're using a new enough deployment target, and we can find a
+  // DefaultExecutorFactory type, call swift_createExecutors()
+  Type factoryNonCanTy = SGM.getConfiguredExecutorFactory();
 
-      if (!factoryTy) {
-        ctx.Diags.diagnose(SourceLoc(), diag::cannot_find_executor_factory_type,
-                           *ctx.LangOpts.ExecutorFactory);
-      }
+  if (isCreateExecutorsFunctionAvailable(SGM) && factoryNonCanTy) {
+    CanType factoryTy = factoryNonCanTy->getCanonicalType();
 
-      ProtocolDecl *executorFactoryProtocol
-        = ctx.getProtocol(KnownProtocolKind::ExecutorFactory);
-      auto conformance = lookupConformance(factoryTy, executorFactoryProtocol);
+    ProtocolDecl *executorFactoryProtocol
+      = ctx.getProtocol(KnownProtocolKind::ExecutorFactory);
+    auto conformance = lookupConformance(factoryTy, executorFactoryProtocol);
 
-      if (conformance.isInvalid()) {
-        // If this type doesn't conform, ignore it and use the default factory
-        SourceLoc loc = extractNearestSourceLoc(factoryTy);
+    if (conformance.isInvalid()) {
+      // If this type doesn't conform, ignore it and use the default factory
+      SourceLoc loc = extractNearestSourceLoc(factoryTy);
 
-        ctx.Diags.diagnose(loc, diag::executor_factory_must_conform,
-                           *ctx.LangOpts.ExecutorFactory);
+      ctx.Diags.diagnose(loc, diag::executor_factory_must_conform);
 
-        factoryTy = SGM.getDefaultExecutorFactory()->getCanonicalType();
-        conformance = lookupConformance(factoryTy, executorFactoryProtocol);
+      factoryTy = SGM.getDefaultExecutorFactory()->getCanonicalType();
+      conformance = lookupConformance(factoryTy, executorFactoryProtocol);
 
-        assert(!conformance.isInvalid());
-      }
+      assert(!conformance.isInvalid());
+    }
 
-      FuncDecl *createExecutorsFuncDecl = SGM.getCreateExecutors();
-      assert(createExecutorsFuncDecl
-             && "Failed to find swift_createExecutors function decl");
-      SILFunction *createExecutorsSILFunc =
-        SGM.getFunction(SILDeclRef(createExecutorsFuncDecl, SILDeclRef::Kind::Func),
+    FuncDecl *createExecutorsFuncDecl = SGM.getCreateExecutors();
+    assert(createExecutorsFuncDecl
+           && "Failed to find swift_createExecutors function decl");
+    SILFunction *createExecutorsSILFunc =
+      SGM.getFunction(SILDeclRef(createExecutorsFuncDecl, SILDeclRef::Kind::Func),
                         NotForDefinition);
-      SILValue createExecutorsFunc =
-        B.createFunctionRefFor(moduleLoc, createExecutorsSILFunc);
-      MetatypeType *factoryThickMetaTy
-        = MetatypeType::get(factoryTy, MetatypeRepresentation::Thick);
-      SILValue factorySILMetaTy
-        = B.createMetatype(moduleLoc, getLoweredType(factoryThickMetaTy));
-      auto ceSubs = SubstitutionMap::getProtocolSubstitutions(
-        conformance.getProtocol(), factoryTy, conformance);
-      B.createApply(moduleLoc, createExecutorsFunc, ceSubs, { factorySILMetaTy });
-    }
+    SILValue createExecutorsFunc =
+      B.createFunctionRefFor(moduleLoc, createExecutorsSILFunc);
+    MetatypeType *factoryThickMetaTy
+      = MetatypeType::get(factoryTy, MetatypeRepresentation::Thick);
+    SILValue factorySILMetaTy
+      = B.createMetatype(moduleLoc, getLoweredType(factoryThickMetaTy));
+    auto ceSubs = SubstitutionMap::getProtocolSubstitutions(
+      conformance.getProtocol(), factoryTy, conformance);
+    B.createApply(moduleLoc, createExecutorsFunc, ceSubs, { factorySILMetaTy });
   }
 
   auto wrapCallArgs = [this, &moduleLoc](SILValue originalValue, FuncDecl *fd,

Diff for: stdlib/public/Concurrency/Executor.swift

@@ -534,6 +534,9 @@ public protocol ExecutorFactory {
   static var defaultExecutor: any TaskExecutor { get }
 }
 
+@available(SwiftStdlib 6.2, *)
+typealias DefaultExecutorFactory = PlatformExecutorFactory
+
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_createExecutors")
 public func _createExecutors<F: ExecutorFactory>(factory: F.Type) {
@@ -556,7 +559,7 @@ extension MainActor {
   @available(SwiftStdlib 6.2, *)
   public static var executor: any MainExecutor {
     if _executor == nil {
-      _executor = PlatformExecutorFactory.mainExecutor
+      _executor = DefaultExecutorFactory.mainExecutor
     }
     return _executor!
   }
@@ -575,7 +578,7 @@ extension Task where Success == Never, Failure == Never {
   @available(SwiftStdlib 6.2, *)
   public static var defaultExecutor: any TaskExecutor {
     if _defaultExecutor == nil {
-      _defaultExecutor = PlatformExecutorFactory.defaultExecutor
+      _defaultExecutor = DefaultExecutorFactory.defaultExecutor
     }
     return _defaultExecutor!
   }

Diff for: test/Concurrency/Runtime/custom_main_executor.swift

@@ -1,4 +1,4 @@
-// RUN: %target-run-simple-swift(-Xfrontend -disable-availability-checking -g %import-libdispatch -parse-as-library -executor-factory SimpleExecutorFactory) | %FileCheck %s
+// RUN: %target-run-simple-swift(-Xfrontend -disable-availability-checking -g %import-libdispatch -parse-as-library) | %FileCheck %s
 
 // REQUIRES: concurrency
 // REQUIRES: executable_test
@@ -13,6 +13,8 @@
 import StdlibUnittest
 import Synchronization
 
+typealias DefaultExecutorFactory = SimpleExecutorFactory
+
 struct SimpleExecutorFactory: ExecutorFactory {
   public static var mainExecutor: any MainExecutor {
     print("Creating main executor")