[ClangImporter] Import 'swift_attr("sending")' As a Type Attribute

Previously, `__attribute__((swift_attr("sending")))` would only be
resolved when attached to declarations. This patch expands it to be
a type attribute as well, which enables it to occur in the result and
parameter positions for blocks, function pointers, and lambdas.

Resolves rdar://148435359

lib/ClangImporter/ImportType.cpp

@@ -726,20 +726,45 @@ namespace {
             paramQualType->getPointeeType().isConstQualified())
           paramQualType = paramQualType->getPointeeType();
 
+        // Mark any `sending` parameters if need be.
+        ImportTypeAttrs paramAttributes;
+        if (Impl.SwiftContext.LangOpts.hasFeature(Feature::SendingArgsAndResults)) {
+          getConcurrencyAttrs(Impl.SwiftContext, ImportTypeKind::Parameter,
+                              paramAttributes, paramQualType);
+        }
+
         auto swiftParamTy = Impl.importTypeIgnoreIUO(
             paramQualType, paramImportKind, addImportDiagnostic,
             AllowNSUIntegerAsInt, Bridging, ImportTypeAttrs(), OTK_Optional);
         if (!swiftParamTy)
           return Type();
 
+        ParameterTypeFlags flags;
+        flags = flags.withSending(
+            paramAttributes.contains(ImportTypeAttr::Sending));
+
         // FIXME(https://github.com/apple/swift/issues/45134): If we were walking TypeLocs, we could actually get parameter names.
         // The probably doesn't matter outside of a FuncDecl, which we'll have
         // to special-case, but it's an interesting bit of data loss.
-        params.push_back(FunctionType::Param(swiftParamTy));
+        params.emplace_back(swiftParamTy, Identifier(), flags);
+      }
+
+      // Mark any `sending` result types if need be.
+      auto extInfo = FunctionType::ExtInfo();
+      ImportTypeAttrs resultAttributes;
+      if (Impl.SwiftContext.LangOpts.hasFeature(Feature::SendingArgsAndResults)) {
+        getConcurrencyAttrs(Impl.SwiftContext, ImportTypeKind::Result,
+                            resultAttributes, type->getReturnType());
+
+        const bool sending = resultAttributes.contains(ImportTypeAttr::Sending);
+        extInfo = FunctionType::ExtInfo()
+                           .intoBuilder()
+                           .withSendingResult(sending)
+                           .build();
       }
 
       // Form the function type.
-      return FunctionType::get(params, resultTy, FunctionType::ExtInfo());
+      return FunctionType::get(params, resultTy, extInfo);
     }
 
     ImportResult
@@ -1714,6 +1739,7 @@ void swift::getConcurrencyAttrs(ASTContext &SwiftContext,
       SwiftContext.LangOpts.hasFeature(Feature::SendableCompletionHandlers) &&
       importKind == ImportTypeKind::CompletionHandlerParameter;
   bool isNonSendable = false;
+  bool isSending = false;
 
   // Consider only immediate attributes, don't look through the typerefs
   // because they are imported separately.
@@ -1721,10 +1747,13 @@ void swift::getConcurrencyAttrs(ASTContext &SwiftContext,
     if (isMainActorAttr(attr)) {
       isMainActor = true;
       isSendable = true; // MainActor implies Sendable
-    } else if (attr->getAttribute() == "@Sendable")
+    } else if (attr->getAttribute() == "@Sendable") {
       isSendable = true;
-    else if (attr->getAttribute() == "@_nonSendable")
+    } else if (attr->getAttribute() == "@_nonSendable") {
       isNonSendable = true;
+    } else if (attr->getAttribute() == "sending") {
+      isSending = true;
+    }
   });
 
   if (isMainActor)
@@ -1733,6 +1762,8 @@ void swift::getConcurrencyAttrs(ASTContext &SwiftContext,
     attrs |= ImportTypeAttr::Sendable;
   if (isNonSendable)
     attrs -= ImportTypeAttr::Sendable;
+  if (isSending)
+    attrs |= ImportTypeAttr::Sending;
 }
 
 ImportedType ClangImporter::Implementation::importType(

lib/ClangImporter/ImporterImpl.h

@@ -217,6 +217,10 @@ enum class ImportTypeAttr : uint8_t {
   ///
   /// This ensures that the parameter is not marked as Unmanaged.
   CFUnretainedOutParameter = 1 << 5,
+
+  /// Type should be imported as though declaration was marked with
+  /// \c __attribute__((swift_attr("sending"))) .
+  Sending = 1 << 6,
 };
 
 /// Find and iterate over swift attributes embedded in the type

test/ClangImporter/Inputs/sending.h

@@ -43,4 +43,7 @@ sendUserDefinedFromGlobalFunction(NonSendableCStruct other) SWIFT_SENDING;
 void sendUserDefinedIntoGlobalFunction(
     NonSendableCStruct arg SWIFT_SENDING);
 
+void sendingWithCompletionHandler(void (^completion)(SWIFT_SENDING NonSendableCStruct arg));
+SWIFT_SENDING NonSendableCStruct sendingWithLazyReturn(SWIFT_SENDING NonSendableCStruct (^makeLazily)(void));
+
 #pragma clang assume_nonnull end

test/ClangImporter/sending.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -swift-version 6 -disable-availability-checking -emit-sil -o /dev/null %s -parse-as-library -enable-experimental-feature SendingArgsAndResults -verify -import-objc-header %S/Inputs/sending.h
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk-nosource -I %t) -swift-version 6 -disable-availability-checking -emit-sil -o /dev/null %s -parse-as-library -enable-experimental-feature SendingArgsAndResults -verify -import-objc-header %S/Inputs/sending.h
 
 // REQUIRES: concurrency
 // REQUIRES: swift_feature_SendingArgsAndResults
@@ -38,3 +38,18 @@ func funcTestSendingArg() async {
   // expected-note @-1 {{'x' used after being passed as a 'sending' parameter}}
   useValue(x) // expected-note {{access can happen concurrently}}
 }
+
+func funcTestSendingClosureArg() async {
+  sendingWithCompletionHandler { (x: sending NonSendableCStruct) in
+    sendUserDefinedIntoGlobalFunction(x) // expected-error {{sending 'x' risks causing data races}}
+    // expected-note @-1 {{'x' used after being passed as a 'sending' parameter}}
+    useValue(x) // expected-note {{access can happen concurrently}}
+  }
+
+  let x = sendingWithLazyReturn { () -> sending NonSendableCStruct in
+    NonSendableCStruct()
+  }
+  sendUserDefinedIntoGlobalFunction(x) // expected-error {{sending 'x' risks causing data races}}
+  // expected-note @-1 {{'x' used after being passed as a 'sending' parameter}}
+  useValue(x) // expected-note {{access can happen concurrently}}
+}