Add support for @Concurrent attribute on closures.

Author: DougGregor

lib/Sema/ConstraintSystem.cpp

@@ -2358,17 +2358,19 @@ FunctionType::ExtInfo ConstraintSystem::closureEffects(ClosureExpr *expr) {
   // set of effects.
   bool throws = expr->getThrowsLoc().isValid();
   bool async = expr->getAsyncLoc().isValid();
+  bool concurrent = expr->getAttrs().hasAttribute<ConcurrentAttr>();
   if (throws || async) {
     return ASTExtInfoBuilder()
       .withThrows(throws)
       .withAsync(async)
+      .withConcurrent(concurrent)
       .build();
   }
 
   // Scan the body to determine the effects.
   auto body = expr->getBody();
   if (!body)
-    return FunctionType::ExtInfo();
+    return ASTExtInfoBuilder().withConcurrent(concurrent).build();
 
   auto throwFinder = FindInnerThrows(*this, expr);
   body->walk(throwFinder);
@@ -2377,6 +2379,7 @@ FunctionType::ExtInfo ConstraintSystem::closureEffects(ClosureExpr *expr) {
   auto result = ASTExtInfoBuilder()
     .withThrows(throwFinder.foundThrow())
     .withAsync(asyncFinder.foundAsync())
+    .withConcurrent(concurrent)
     .build();
   closureEffectsCache[expr] = result;
   return result;

lib/Sema/TypeCheckAttr.cpp

@@ -5482,10 +5482,9 @@ namespace {
 class ClosureAttributeChecker
     : public AttributeVisitor<ClosureAttributeChecker> {
   ASTContext &ctx;
-  ClosureExpr *closure;
 public:
   ClosureAttributeChecker(ClosureExpr *closure)
-    : ctx(closure->getASTContext()), closure(closure) { }
+    : ctx(closure->getASTContext()) { }
 
   void visitDeclAttribute(DeclAttribute *attr) {
     ctx.Diags.diagnose(
@@ -5494,6 +5493,10 @@ class ClosureAttributeChecker
       .fixItRemove(attr->getRangeWithAt());
     attr->setInvalid();
   }
+
+  void visitConcurrentAttr(ConcurrentAttr *attr) {
+    // Nothing else to check.
+  }
 };
 
 }

test/attr/attr_concurrent.swift

@@ -118,3 +118,10 @@ func testCaseNonTrivialValue() {
 
   j = 17
 }
+
+func testExplicitConcurrentClosure() {
+  let fn = { @concurrent in
+    17
+  }
+  let _: String = fn // expected-error{{cannot convert value of type '@concurrent () -> Int' to specified type 'String'}}
+}