Add support for @Concurrent on function declarations

Author: DougGregor

include/swift/AST/Attr.def

@@ -600,6 +600,12 @@ CONTEXTUAL_SIMPLE_DECL_ATTR(async, Async,
   APIBreakingToAdd | APIBreakingToRemove,
   106)
 
+SIMPLE_DECL_ATTR(concurrent, Concurrent,
+  OnFunc | OnConstructor | OnAccessor | ConcurrencyOnly |
+  ABIStableToAdd | ABIStableToRemove |
+  APIBreakingToAdd | APIBreakingToRemove,
+  107)
+
 #undef TYPE_ATTR
 #undef DECL_ATTR_ALIAS
 #undef CONTEXTUAL_DECL_ATTR_ALIAS

lib/Sema/TypeCheckAttr.cpp

@@ -121,6 +121,7 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   IGNORED_ATTR(OriginallyDefinedIn)
   IGNORED_ATTR(NoDerivative)
   IGNORED_ATTR(SpecializeExtension)
+  IGNORED_ATTR(Concurrent)
 #undef IGNORED_ATTR
 
   void visitAlignmentAttr(AlignmentAttr *attr) {

lib/Sema/TypeCheckDecl.cpp

@@ -2524,6 +2524,8 @@ InterfaceTypeRequest::evaluate(Evaluator &eval, ValueDecl *D) const {
       AFD->getParameters()->getParams(argTy);
 
       infoBuilder = infoBuilder.withAsync(AFD->hasAsync());
+      infoBuilder = infoBuilder.withConcurrent(
+          AFD->getAttrs().hasAttribute<ConcurrentAttr>());
       // 'throws' only applies to the innermost function.
       infoBuilder = infoBuilder.withThrows(AFD->hasThrows());
       // Defer bodies must not escape.

lib/Sema/TypeCheckDeclOverride.cpp

@@ -1531,7 +1531,8 @@ namespace  {
     UNINTERESTING_ATTR(ActorIndependent)
     UNINTERESTING_ATTR(GlobalActor)
     UNINTERESTING_ATTR(Async)
-    
+    UNINTERESTING_ATTR(Concurrent)
+
     UNINTERESTING_ATTR(AtRethrows)
 #undef UNINTERESTING_ATTR
 

test/attr/attr_concurrent.swift

@@ -18,6 +18,8 @@ func onEscapingAutoclosure2(_ fn: @escaping @autoclosure @concurrent () -> Int)
 func acceptsConcurrent(_ fn: @concurrent (Int) -> Int) { }
 func acceptsNonConcurrent(_ fn: (Int) -> Int) { }
 
+@concurrent func negate(_ x: Int) -> Int { -x }
+
 func passingConcurrentOrNot(
   _ cfn: @concurrent (Int) -> Int,
   ncfn: (Int) -> Int // expected-note{{parameter 'ncfn' is implicitly non-concurrent}}{{9-9=@concurrent }}
@@ -30,6 +32,11 @@ func passingConcurrentOrNot(
   acceptsConcurrent(ncfn) // expected-error{{passing non-concurrent parameter 'ncfn' to function expecting a @concurrent closure}}
   acceptsNonConcurrent(cfn) // okay
   acceptsNonConcurrent(ncfn) // okay
+
+  acceptsConcurrent(negate)
+  acceptsNonConcurrent(negate)
+
+  let _: Int = negate // expected-error{{cannot convert value of type '@concurrent (Int) -> Int' to specified type 'Int'}}
 }
 
 func closures() {
@@ -45,3 +52,4 @@ func closures() {
   let closure1 = { $0 + 1 } // inferred to be non-concurrent
   acceptsConcurrent(closure1) // expected-error{{converting non-concurrent function value to '@concurrent (Int) -> Int' may introduce data races}}
 }
+