[AST/Sema] Hide using declaration behind DefaultIsolationPerFile experimental feature

(cherry picked from commit c246a7a372)

include/swift/AST/DiagnosticsParse.def

@@ -2186,6 +2186,8 @@ ERROR(nonisolated_nonsending_repeated,none,
 ERROR(using_decl_invalid_specifier,PointsToFirstBadToken,
       "'using' declaration does not support %0 %select{modifier|attribute}1",
       (Identifier, bool))
+ERROR(experimental_using_decl_disabled,PointsToFirstBadToken,
+      "'using' is an experimental feature that is currently disabled", ())
 
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

include/swift/Basic/Features.def

@@ -522,6 +522,10 @@ EXPERIMENTAL_FEATURE(AllowRuntimeSymbolDeclarations, true)
 /// Optimize copies of ObjectiveC blocks.
 EXPERIMENTAL_FEATURE(CopyBlockOptimization, true)
 
+/// Allow use of `using` declaration that control default isolation
+/// in a file scope.
+EXPERIMENTAL_FEATURE(DefaultIsolationPerFile, false)
+
 #undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE

lib/AST/FeatureSet.cpp

@@ -632,6 +632,10 @@ static bool usesFeatureAlwaysInheritActorContext(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureDefaultIsolationPerFile(Decl *D) {
+  return isa<UsingDecl>(D);
+}
+
 // ----------------------------------------------------------------------------
 // MARK: - FeatureSet
 // ----------------------------------------------------------------------------

lib/ASTGen/Sources/ASTGen/SourceFile.swift

@@ -78,6 +78,7 @@ extension Parser.ExperimentalFeatures {
     mapFeature(.OldOwnershipOperatorSpellings, to: .oldOwnershipOperatorSpellings)
     mapFeature(.KeyPathWithMethodMembers, to: .keypathWithMethodMembers)
     mapFeature(.InlineArrayTypeSugar, to: .inlineArrayTypeSugar)
+    mapFeature(.DefaultIsolationPerFile, to: .defaultIsolationPerFile)
   }
 }
 

lib/Parse/ParseDecl.cpp

@@ -6647,6 +6647,10 @@ ParserResult<UsingDecl> Parser::parseDeclUsing(ParseDeclOptions Flags,
   assert(Tok.isContextualKeyword("using"));
   DebuggerContextChange DCC(*this);
 
+  if (!Context.LangOpts.hasFeature(Feature::DefaultIsolationPerFile)) {
+    diagnose(Tok, diag::experimental_using_decl_disabled);
+  }
+
   SourceLoc UsingLoc = consumeToken();
 
   if (Tok.is(tok::code_complete)) {

test/ASTGen/decls.swift

@@ -2,19 +2,22 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend-dump-parse -disable-availability-checking -enable-experimental-move-only -enable-experimental-concurrency -enable-experimental-feature ParserASTGen \
 // RUN:    -enable-experimental-feature CoroutineAccessors \
+// RUN:    -enable-experimental-feature DefaultIsolationPerFile \
 // RUN:    | %sanitize-address > %t/astgen.ast
 // RUN: %target-swift-frontend-dump-parse -disable-availability-checking -enable-experimental-move-only -enable-experimental-concurrency \
 // RUN:    -enable-experimental-feature CoroutineAccessors \
+// RUN:    -enable-experimental-feature DefaultIsolationPerFile \
 // RUN:    | %sanitize-address > %t/cpp-parser.ast
 
 // RUN: %diff -u %t/astgen.ast %t/cpp-parser.ast
 
-// RUN: %target-run-simple-swift(-Xfrontend -disable-availability-checking -Xfrontend -enable-experimental-concurrency -enable-experimental-feature CoroutineAccessors -enable-experimental-feature ParserASTGen)
+// RUN: %target-run-simple-swift(-Xfrontend -disable-availability-checking -Xfrontend -enable-experimental-concurrency -enable-experimental-feature CoroutineAccessors -enable-experimental-feature DefaultIsolationPerFile -enable-experimental-feature ParserASTGen)
 
 // REQUIRES: executable_test
 // REQUIRES: swift_swift_parser
 // REQUIRES: swift_feature_ParserASTGen
 // REQUIRES: swift_feature_CoroutineAccessors
+// REQUIRES: swift_feature_DefaultIsolationPerFile
 
 // rdar://116686158
 // UNSUPPORTED: asan

test/ASTGen/diagnostics.swift

@@ -1,9 +1,13 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-typecheck-verify-swift -disable-availability-checking -enable-bare-slash-regex -enable-experimental-feature ParserASTGen
+// RUN: %target-typecheck-verify-swift -disable-availability-checking \
+// RUN:   -enable-bare-slash-regex \
+// RUN:   -enable-experimental-feature ParserASTGen \
+// RUN:   -enable-experimental-feature DefaultIsolationPerFile
 
 // REQUIRES: swift_swift_parser
 // REQUIRES: swift_feature_ParserASTGen
+// REQUIRES: swift_feature_DefaultIsolationPerFile
 
 // rdar://116686158
 // UNSUPPORTED: asan
@@ -75,4 +79,4 @@ using @Test
 // expected-error@-1 {{default isolation can only be set to '@MainActor' or 'nonisolated'}}
 
 using test
-// expected-error@-1 {{default isolation can only be set to '@MainActor' or 'nonisolated'}}
+// expected-error@-1 {{default isolation can only be set to '@MainActor' or 'nonisolated'}}

test/ModuleInterface/using.swift

@@ -1,9 +1,11 @@
-// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %s
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %s -enable-experimental-feature DefaultIsolationPerFile
 
 // RUN: %target-swift-typecheck-module-from-interface(%t.swiftinterface)
 
 // RUN: %FileCheck %s --input-file %t.swiftinterface
 
+// REQUIRES: swift_feature_DefaultIsolationPerFile
+
 using @MainActor
 
 // CHECK-NOT: using @MainActor

test/Parse/using.swift

@@ -1,4 +1,6 @@
-// RUN: %target-typecheck-verify-swift
+// RUN: %target-typecheck-verify-swift -enable-experimental-feature DefaultIsolationPerFile
+
+// REQUIRES: swift_feature_DefaultIsolationPerFile
 
 // REQUIRES: concurrency