[Clang importer] Import __swift_attr__("@sendable") as Sendable on parameters.

Author: DougGregor

lib/ClangImporter/ImportType.cpp

@@ -1739,6 +1739,15 @@ Type ClangImporter::Implementation::applyParamAttributes(
 
       continue;
     }
+
+    // Map @Sendable.
+    if (swiftAttr->getAttribute() == "@Sendable") {
+      type = applyToFunctionType(type, [](ASTExtInfo extInfo) {
+        return extInfo.withConcurrent();
+      });
+
+      continue;
+    }
   }
 
   return type;

test/ClangImporter/objc_async.swift

@@ -82,6 +82,18 @@ func testSlowServerOldSchool(slowServer: SlowServer) {
   _ = slowServer.allOperations
 }
 
+func testSendable(fn: () -> Void) { // expected-note{{parameter 'fn' is implicitly non-concurrent}}
+  doSomethingConcurrently(fn)
+  // expected-error@-1{{passing non-concurrent parameter 'fn' to function expecting a @Sendable closure}}
+
+  var x = 17
+  doSomethingConcurrently {
+    print(x) // expected-error{{reference to captured var 'x' in concurrently-executing code}}
+    x = x + 1 // expected-error{{mutation of captured var 'x' in concurrently-executing code}}
+    // expected-error@-1{{reference to captured var 'x' in concurrently-executing code}}
+  }
+}
+
 // Check import of attributes
 func globalAsync() async { }
 

test/IDE/print_clang_objc_async.swift

@@ -47,3 +47,5 @@ import _Concurrency
 // CHECK-NEXT: {{^[}]$}}
 
 // CHECK: {{^}}var MAGIC_NUMBER: Int32 { get }
+
+// CHECK: func doSomethingConcurrently(_ block: @Sendable () -> Void)

test/Inputs/clang-importer-sdk/usr/include/ObjCConcurrency.h

@@ -144,4 +144,7 @@ __attribute__((__swift_attr__("@MainActor(unsafe)")))
 -(void)onButtonPress;
 @end
 
+// Do something concurrently, but without escaping.
+void doSomethingConcurrently(__attribute__((noescape)) __attribute__((swift_attr("@Sendable"))) void (^block)(void));
+
 #pragma clang assume_nonnull end