Allow the @Concurrent function attribute without the concurrency flag

Author: DougGregor

include/swift/AST/Attr.def

@@ -602,8 +602,8 @@ CONTEXTUAL_SIMPLE_DECL_ATTR(async, Async,
   106)
 
 SIMPLE_DECL_ATTR(concurrent, Concurrent,
-  OnFunc | OnConstructor | OnAccessor | ConcurrencyOnly |
-  ABIStableToAdd | ABIStableToRemove |
+  OnFunc | OnConstructor | OnAccessor |
+  ABIBreakingToAdd | ABIBreakingToRemove |
   APIBreakingToAdd | APIBreakingToRemove,
   107)
 

lib/Sema/TypeCheckType.cpp

@@ -2339,17 +2339,7 @@ TypeResolver::resolveAttributedType(TypeAttributes &attrs, TypeRepr *repr,
         }
       }
 
-      bool concurrent = false;
-      if (attrs.has(TAK_concurrent)) {
-        if (getASTContext().LangOpts.EnableExperimentalConcurrency) {
-          concurrent = true;
-        } else {
-          diagnoseInvalid(repr, attrs.getLoc(TAK_concurrent),
-                          diag::attr_requires_concurrency,
-                          TypeAttributes::getAttrName(TAK_concurrent),
-                          false);
-        }
-      }
+      bool concurrent = attrs.has(TAK_concurrent);
 
       ty = resolveASTFunctionType(fnRepr, options, rep, /*noescape=*/false,
                                   concurrent, parsedClangFunctionType,

test/IDE/complete_decl_attribute.swift

@@ -71,6 +71,7 @@ struct MyStruct {}
 // KEYWORD2-NEXT:             Keyword/None:                       derivative[#Func Attribute#]; name=derivative
 // KEYWORD2-NEXT:             Keyword/None:                       transpose[#Func Attribute#]; name=transpose
 // KEYWORD2-NEXT:             Keyword/None:                       noDerivative[#Func Attribute#]; name=noDerivative
+// KEYWORD2-NEXT:             Keyword/None:          concurrent[#Func Attribute#]; name=concurrent
 // KEYWORD2-NOT:              Keyword
 // KEYWORD2:                  Decl[Struct]/CurrModule:            MyStruct[#MyStruct#]; name=MyStruct
 // KEYWORD2:                  End completions
@@ -190,6 +191,7 @@ struct _S {
 // ON_METHOD-DAG: Keyword/None:                       differentiable[#Func Attribute#]; name=differentiable
 // ON_METHOD-DAG: Keyword/None:                       derivative[#Func Attribute#]; name=derivative
 // ON_METHOD-DAG: Keyword/None:                       transpose[#Func Attribute#]; name=transpose
+// ON_METHOD-DAG: Keyword/None:                       concurrent[#Func Attribute#]; name=concurrent
 // ON_METHOD-DAG: Keyword/None:                       noDerivative[#Func Attribute#]; name=noDerivative
 // ON_METHOD-NOT: Keyword
 // ON_METHOD: Decl[Struct]/CurrModule:            MyStruct[#MyStruct#]; name=MyStruct
@@ -251,6 +253,7 @@ struct _S {
 // ON_MEMBER_LAST-DAG: Keyword/None:                       derivative[#Declaration Attribute#]; name=derivative
 // ON_MEMBER_LAST-DAG: Keyword/None:                       transpose[#Declaration Attribute#]; name=transpose
 // ON_MEMBER_LAST-DAG: Keyword/None:                       noDerivative[#Declaration Attribute#]; name=noDerivative
+// ON_MEMBER_LAST-DAG: Keyword/None:                       concurrent[#Declaration Attribute#]; name=concurrent
 // ON_MEMBER_LAST-NOT: Keyword
 // ON_MEMBER_LAST: Decl[Struct]/CurrModule:            MyStruct[#MyStruct#]; name=MyStruct
 // ON_MEMBER_LAST-NOT: Decl[PrecedenceGroup]
@@ -300,6 +303,7 @@ func dummy2() {}
 // KEYWORD_LAST-NEXT:             Keyword/None:                       derivative[#Declaration Attribute#]; name=derivative
 // KEYWORD_LAST-NEXT:             Keyword/None:                       transpose[#Declaration Attribute#]; name=transpose
 // KEYWORD_LAST-NEXT:             Keyword/None:                       noDerivative[#Declaration Attribute#]; name=noDerivative
+// KEYWORD_LAST-NEXT:             Keyword/None:                       concurrent[#Declaration Attribute#]; name=concurrent
 // KEYWORD_LAST-NOT:              Keyword
 // KEYWORD_LAST: Decl[Struct]/CurrModule:            MyStruct[#MyStruct#]; name=MyStruct
 // KEYWORD_LAST:                  End completions

test/attr/attr_concurrent.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -typecheck -verify %s -enable-experimental-concurrency -enable-experimental-flow-sensitive-concurrent-captures
+// RUN: %target-swift-frontend -typecheck -verify %s -enable-experimental-flow-sensitive-concurrent-captures
 // REQUIRES: concurrency
 
 // Concurrent attribute on a function type.