Add #[swift_bridge(Sendable)] attribute (#317)

This commit introduces a new `#[swift_bridge(Sendable)]`
attribute that emits Swift `Sendable` implementations for opaque
Rust types, and Rust `Send + Sync` implementations for opaque
Swift types.

These implementations are checked at compile time.

Example usage:
```rust
mod ffi {
    extern "Rust" {
        #[swift_bridge(Sendable)]
        type MyRustType;
    }

    extern "Swift" {
        #[swift_bridge(Sendable)]
        type MySwiftType;
    }
}
```

Author: chinedufn

SwiftRustIntegrationTestRunner/SwiftRustIntegrationTestRunner.xcodeproj/project.pbxproj

@@ -21,7 +21,7 @@
 		220432EC27530AFC00BAE645 /* RustFnUsesOpaqueSwiftTypeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 220432EB27530AFC00BAE645 /* RustFnUsesOpaqueSwiftTypeTests.swift */; };
 		22046383282B4E3F00A09119 /* FunctionAttributeGetTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 22046382282B4E3F00A09119 /* FunctionAttributeGetTests.swift */; };
 		221E16B42786233600F94AC0 /* ConditionalCompilationTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 221E16B32786233600F94AC0 /* ConditionalCompilationTests.swift */; };
-		221E16B62786F9FF00F94AC0 /* OpaqueTypeAttributeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 221E16B52786F9FF00F94AC0 /* OpaqueTypeAttributeTests.swift */; };
+		221E16B62786F9FF00F94AC0 /* AlreadyDeclaredAttributeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 221E16B52786F9FF00F94AC0 /* AlreadyDeclaredAttributeTests.swift */; };
 		222A81E928EB5BB100D4A412 /* Primitive.swift in Sources */ = {isa = PBXBuildFile; fileRef = 222A81E828EB5BB100D4A412 /* Primitive.swift */; };
 		222A81EB28EB5DF800D4A412 /* PrimitiveTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 222A81EA28EB5DF800D4A412 /* PrimitiveTests.swift */; };
 		22553324281DB5FC008A3121 /* GenericTests.rs.swift in Sources */ = {isa = PBXBuildFile; fileRef = 22553323281DB5FC008A3121 /* GenericTests.rs.swift */; };
@@ -57,6 +57,8 @@
 		22FD1C562753CB3F00F64281 /* SwiftFnUsesOpaqueRustTypeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 22FD1C552753CB3F00F64281 /* SwiftFnUsesOpaqueRustTypeTests.swift */; };
 		C926E4DE294F07AA0027E7E2 /* FunctionAttributes.swift in Sources */ = {isa = PBXBuildFile; fileRef = C926E4DD294F07AA0027E7E2 /* FunctionAttributes.swift */; };
 		C926E4E0294F18C50027E7E2 /* FunctionAttributeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = C926E4DF294F18C50027E7E2 /* FunctionAttributeTests.swift */; };
+		DE9444DC2D5241AD007A83A4 /* SendableAttributeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = DE9444DB2D5241A8007A83A4 /* SendableAttributeTests.swift */; };
+		DE9444DE2D527C3B007A83A4 /* SendableAttribute.swift in Sources */ = {isa = PBXBuildFile; fileRef = DE9444DD2D527C31007A83A4 /* SendableAttribute.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -84,7 +86,7 @@
 		220432EB27530AFC00BAE645 /* RustFnUsesOpaqueSwiftTypeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RustFnUsesOpaqueSwiftTypeTests.swift; sourceTree = "<group>"; };
 		22046382282B4E3F00A09119 /* FunctionAttributeGetTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FunctionAttributeGetTests.swift; sourceTree = "<group>"; };
 		221E16B32786233600F94AC0 /* ConditionalCompilationTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ConditionalCompilationTests.swift; sourceTree = "<group>"; };
-		221E16B52786F9FF00F94AC0 /* OpaqueTypeAttributeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OpaqueTypeAttributeTests.swift; sourceTree = "<group>"; };
+		221E16B52786F9FF00F94AC0 /* AlreadyDeclaredAttributeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AlreadyDeclaredAttributeTests.swift; sourceTree = "<group>"; };
 		222A81E828EB5BB100D4A412 /* Primitive.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Primitive.swift; sourceTree = "<group>"; };
 		222A81EA28EB5DF800D4A412 /* PrimitiveTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PrimitiveTests.swift; sourceTree = "<group>"; };
 		22553323281DB5FC008A3121 /* GenericTests.rs.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GenericTests.rs.swift; sourceTree = "<group>"; };
@@ -126,6 +128,8 @@
 		22FD1C552753CB3F00F64281 /* SwiftFnUsesOpaqueRustTypeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SwiftFnUsesOpaqueRustTypeTests.swift; sourceTree = "<group>"; };
 		C926E4DD294F07AA0027E7E2 /* FunctionAttributes.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FunctionAttributes.swift; sourceTree = "<group>"; };
 		C926E4DF294F18C50027E7E2 /* FunctionAttributeTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FunctionAttributeTests.swift; sourceTree = "<group>"; };
+		DE9444DB2D5241A8007A83A4 /* SendableAttributeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SendableAttributeTests.swift; sourceTree = "<group>"; };
+		DE9444DD2D527C31007A83A4 /* SendableAttribute.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SendableAttribute.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -189,6 +193,7 @@
 				22EE4E0828B5388000FEC83C /* SwiftFnUsesOpaqueSwiftType.swift */,
 				22C0625228CE699D007A6F67 /* Callbacks.swift */,
 				225908FD28DA0F9F0080C737 /* Result.swift */,
+				DE9444DD2D527C31007A83A4 /* SendableAttribute.swift */,
 				22BC4BBB294BA0EC0032B8A8 /* SharedEnumAttributes.swift */,
 				C926E4DD294F07AA0027E7E2 /* FunctionAttributes.swift */,
 				1784BE2729CE86D600AE5A4A /* Tuple.swift */,
@@ -208,32 +213,33 @@
 		228FE5E52740DB6D00805D9E /* SwiftRustIntegrationTestRunnerTests */ = {
 			isa = PBXGroup;
 			children = (
+				221E16B52786F9FF00F94AC0 /* AlreadyDeclaredAttributeTests.swift */,
+				178F1CD2298E97FB00335AA0 /* ArgumentAttributesTest.swift */,
 				22D092A227B7E865009A4C2B /* AsyncTests.swift */,
+				22C0625428CE6C9A007A6F67 /* CallbackTests.swift */,
 				221E16B32786233600F94AC0 /* ConditionalCompilationTests.swift */,
+				C926E4DF294F18C50027E7E2 /* FunctionAttributeTests.swift */,
 				22046382282B4E3F00A09119 /* FunctionAttributeGetTests.swift */,
 				22BCAAB827A2607700686A21 /* FunctionAttributeIdentifiableTests.swift */,
+				22553323281DB5FC008A3121 /* GenericTests.rs.swift */,
 				228FE60F27416C0300805D9E /* OpaqueRustStructTests.swift */,
 				228FE61127428A8D00805D9E /* OpaqueSwiftStructTests.swift */,
-				221E16B52786F9FF00F94AC0 /* OpaqueTypeAttributeTests.swift */,
+				220432A6274C953E00BAE645 /* PointerTests.swift */,
 				22043294274ADA7A00BAE645 /* OptionTests.swift */,
 				225908FB28DA0E320080C737 /* ResultTests.swift */,
-				220432A6274C953E00BAE645 /* PointerTests.swift */,
 				222A81EA28EB5DF800D4A412 /* PrimitiveTests.swift */,
 				220432EB27530AFC00BAE645 /* RustFnUsesOpaqueSwiftTypeTests.swift */,
+				DE9444DB2D5241A8007A83A4 /* SendableAttributeTests.swift */,
 				2202BC0727B2DD1700D43CC4 /* SharedEnumTests.swift */,
 				22BC4BB9294B8CCD0032B8A8 /* SharedEnumAttributeTests.swift */,
 				22C0AD50278ECA9E00A96469 /* SharedStructAttributeTests.swift */,
 				220432AE274E7BF800BAE645 /* SharedStructTests.swift */,
+				2289E82B29A879A7009D89D7 /* SingleRepresentationTypeElisionTests.swift */,
 				228FE5E62740DB6D00805D9E /* StringTests.swift */,
 				22FD1C552753CB3F00F64281 /* SwiftFnUsesOpaqueRustTypeTests.swift */,
-				22043292274A8FDF00BAE645 /* VecTests.swift */,
-				22553323281DB5FC008A3121 /* GenericTests.rs.swift */,
-				2289E82B29A879A7009D89D7 /* SingleRepresentationTypeElisionTests.swift */,
 				22EE4E0A28B538A700FEC83C /* SwiftFnUsesOpaqueSwiftTypeTests.swift */,
-				22C0625428CE6C9A007A6F67 /* CallbackTests.swift */,
-				C926E4DF294F18C50027E7E2 /* FunctionAttributeTests.swift */,
-				178F1CD2298E97FB00335AA0 /* ArgumentAttributesTest.swift */,
 				1745111429BE189B00B96A1A /* TupleTests.swift */,
+				22043292274A8FDF00BAE645 /* VecTests.swift */,
 			);
 			path = SwiftRustIntegrationTestRunnerTests;
 			sourceTree = "<group>";
@@ -407,6 +413,7 @@
 				C926E4DE294F07AA0027E7E2 /* FunctionAttributes.swift in Sources */,
 				228FE64A274919C600805D9E /* swift-integration-tests.swift in Sources */,
 				22C0625328CE699D007A6F67 /* Callbacks.swift in Sources */,
+				DE9444DE2D527C3B007A83A4 /* SendableAttribute.swift in Sources */,
 				22BC10F82799A3A000A0D046 /* SharedStructAttributes.swift in Sources */,
 				22EE4E0928B5388000FEC83C /* SwiftFnUsesOpaqueSwiftType.swift in Sources */,
 				228FE60C2740F42000805D9E /* ASwiftStack.swift in Sources */,
@@ -418,12 +425,13 @@
 			buildActionMask = 2147483647;
 			files = (
 				22043293274A8FDF00BAE645 /* VecTests.swift in Sources */,
-				221E16B62786F9FF00F94AC0 /* OpaqueTypeAttributeTests.swift in Sources */,
+				221E16B62786F9FF00F94AC0 /* AlreadyDeclaredAttributeTests.swift in Sources */,
 				220432A7274C953E00BAE645 /* PointerTests.swift in Sources */,
 				C926E4E0294F18C50027E7E2 /* FunctionAttributeTests.swift in Sources */,
 				220432AF274E7BF800BAE645 /* SharedStructTests.swift in Sources */,
 				178F1CD3298E97FB00335AA0 /* ArgumentAttributesTest.swift in Sources */,
 				2289E82C29A879A7009D89D7 /* SingleRepresentationTypeElisionTests.swift in Sources */,
+				DE9444DC2D5241AD007A83A4 /* SendableAttributeTests.swift in Sources */,
 				220432EC27530AFC00BAE645 /* RustFnUsesOpaqueSwiftTypeTests.swift in Sources */,
 				222A81EB28EB5DF800D4A412 /* PrimitiveTests.swift in Sources */,
 				22553324281DB5FC008A3121 /* GenericTests.rs.swift in Sources */,

SwiftRustIntegrationTestRunner/SwiftRustIntegrationTestRunner/SendableAttribute.swift

@@ -0,0 +1,12 @@
+//
+//  SendableAttribute.swift
+//  SwiftRustIntegrationTestRunner
+//
+//  Created by Frankie Nwafili on 2/4/25.
+//
+
+final class SendableSwiftType {}
+extension SendableSwiftType: Sendable {}
+
+final class AnotherSendableSwiftType {}
+extension AnotherSendableSwiftType: Sendable {}

SwiftRustIntegrationTestRunner/SwiftRustIntegrationTestRunnerTests/OpaqueTypeAttributeTests.swift SwiftRustIntegrationTestRunner/SwiftRustIntegrationTestRunnerTests/AlreadyDeclaredAttributeTests.swift

@@ -1,5 +1,5 @@
 //
-//  OpaqueTypeAttributeTests.swift
+//  AlreadyDeclaredAttributeTests.swift
 //  SwiftRustIntegrationTestRunnerTests
 //
 //  Created by Frankie Nwafili on 1/6/22.

SwiftRustIntegrationTestRunner/SwiftRustIntegrationTestRunnerTests/SendableAttributeTests.swift

@@ -0,0 +1,30 @@
+//
+//  SendableAttributeTests.swift
+//  SwiftRustIntegrationTestRunner
+//
+//  Created by Frankie Nwafili on 2/4/25.
+//
+
+import XCTest
+@testable import SwiftRustIntegrationTestRunner
+
+/// Tests for the `#[swift_bridge(Sendable)]` attribute.
+///
+/// For the corresponding Rust code, see `crates/swift-integration-tests/src/sendable_attribute.rs`.
+/// For the corresponding codegen tests, see `crates/swift-bridge-ir/src/codegen/codegen_tests/sendable_attribute.rs`.
+class SendableAttributeTests: XCTestCase {
+    /// Verify that we can a Rust type that has the `#[swift_bridge(Sendable)]` attribute gets a `Sendable` protocol implementation.
+    func testSendableExternRustType() throws {
+        let sendableRustType = SendableRustType()
+        
+        // Move the type to another thread.
+        Thread.detachNewThread {
+            let _ = sendableRustType;
+        }
+    }
+}
+
+
+protocol AssertIsSendable: Sendable {}
+extension SendableRustType: AssertIsSendable{}
+

book/src/bridge-module/opaque-types/README.md

@@ -266,6 +266,31 @@ table[val] = "world"
 print(table[val])
 ```
 
+#### #[swift_bridge(Sendable)]
+
+The `Sendable` attribute can be added to both opaque Rust and opaque Swift types.
+
+When applied to an opaque Rust type, the generated Swift type will implement Swift's `Sendable` protocol.
+`swift-bridge` will emit code that, at compile time, confirms that the Rust type implements `Send + Sync`.
+
+When applied to an opaque Swift type, the generated Rust type will implement Rust's `Send + Sync` traits.
+`swift-bridge` will emit code that, at compile time, confirms that the Swift type implements `Sendable`.
+
+```rust
+#[swift_bridge::bridge]
+mod ffi {
+    extern "Rust" {
+        #[swift_bridge(Sendable)]
+        type MyRustType;
+    }
+
+    extern "Swift" {
+        #[swift_bridge(Sendable)]
+        type MySwiftType;
+    }
+}
+```
+
 #### #[swift_bridge(__experimental_ownership)]
 
 The `__experimental_ownership` attribute instructs `swift-bridge` to emit code that takes advantage of Swift 6's

crates/swift-bridge-ir/src/codegen/codegen_tests.rs

@@ -34,8 +34,8 @@ mod boxed_fnonce;
 mod built_in_tuple;
 mod c_header_declaration_order;
 mod conditional_compilation;
-mod derive_attribute;
-mod derive_struct_attribute;
+mod derive_copy_clone;
+mod derive_debug;
 mod extern_rust_function_opaque_rust_type_argument;
 mod extern_rust_function_opaque_rust_type_return;
 mod extern_rust_method_swift_class_placement;
@@ -46,6 +46,7 @@ mod opaque_swift_type;
 mod option;
 mod result;
 mod return_into_attribute;
+mod sendable_attribute;
 mod single_representation_type_elision;
 mod string;
 mod transparent_enum;

crates/swift-bridge-ir/src/codegen/codegen_tests/derive_struct_attribute.rs crates/swift-bridge-ir/src/codegen/codegen_tests/derive_copy_clone.rs

@@ -0,0 +1,109 @@
+use super::{ExpectedCHeader, ExpectedRustTokens, ExpectedSwiftCode};
+use proc_macro2::TokenStream;
+use quote::quote;
+
+/// Verify that we can add `#[swift_bridge(Sendable)]` to an extern Rust type.
+mod extern_rust_sendable_attribute {
+    use super::*;
+    use crate::codegen::codegen_tests::CodegenTest;
+
+    fn bridge_module_tokens() -> TokenStream {
+        quote! {
+            mod ffi {
+                extern "Rust" {
+                    #[swift_bridge(Sendable)]
+                    type SomeType;
+                }
+            }
+        }
+    }
+
+    /// Verify that we generate a function that frees the memory behind an opaque pointer to a Rust
+    /// type.
+    fn expected_rust_tokens() -> ExpectedRustTokens {
+        ExpectedRustTokens::Contains(quote! {
+            const fn __swift_bridge__assert_send_sync<T: Send + Sync>() {}
+            const _: () = { __swift_bridge__assert_send_sync::<super::SomeType>() };
+        })
+    }
+
+    fn expected_swift_code() -> ExpectedSwiftCode {
+        ExpectedSwiftCode::ContainsAfterTrim(
+            r#"
+extension SomeType: @unchecked Sendable {}
+"#,
+        )
+    }
+
+    const EXPECTED_C_HEADER: ExpectedCHeader = ExpectedCHeader::ContainsAfterTrim(
+        r#"
+typedef struct SomeType SomeType;
+void __swift_bridge__$SomeType$_free(void* self);
+    "#,
+    );
+
+    #[test]
+    fn extern_rust_type() {
+        CodegenTest {
+            bridge_module: bridge_module_tokens().into(),
+            expected_rust_tokens: expected_rust_tokens(),
+            expected_swift_code: expected_swift_code(),
+            expected_c_header: EXPECTED_C_HEADER,
+        }
+        .test();
+    }
+}
+
+/// Verify that we can add `#[swift_bridge(Sendable)]` to an extern Swift type.
+mod extern_swift_sendable_attribute {
+    use super::*;
+    use crate::codegen::codegen_tests::CodegenTest;
+
+    fn bridge_module_tokens() -> TokenStream {
+        quote! {
+            mod foo {
+                extern "Swift" {
+                    #[swift_bridge(Sendable)]
+                    type SomeSwiftType;
+                }
+            }
+        }
+    }
+
+    fn expected_rust_tokens() -> ExpectedRustTokens {
+        ExpectedRustTokens::Contains(quote! {
+            #[repr(C)]
+            pub struct SomeSwiftType(*mut std::ffi::c_void);
+
+            impl Drop for SomeSwiftType {
+                fn drop (&mut self) {
+                    unsafe { __swift_bridge__SomeSwiftType__free(self.0) }
+                }
+            }
+
+            unsafe impl Send for SomeSwiftType {}
+            unsafe impl Sync for SomeSwiftType {}
+
+        })
+    }
+
+    const EXPECTED_SWIFT_CODE: ExpectedSwiftCode = ExpectedSwiftCode::ContainsAfterTrim(
+        r#"
+protocol __swift_bridge__IsSendable: Sendable {}
+extension SomeSwiftType: __swift_bridge__IsSendable {}
+"#,
+    );
+
+    const EXPECTED_C_HEADER: ExpectedCHeader = ExpectedCHeader::ExactAfterTrim(r#""#);
+
+    #[test]
+    fn extern_swift_type_derive_sendable() {
+        CodegenTest {
+            bridge_module: bridge_module_tokens().into(),
+            expected_rust_tokens: expected_rust_tokens(),
+            expected_swift_code: EXPECTED_SWIFT_CODE,
+            expected_c_header: EXPECTED_C_HEADER,
+        }
+        .test();
+    }
+}

crates/swift-bridge-ir/src/codegen/codegen_tests/derive_attribute.rs crates/swift-bridge-ir/src/codegen/codegen_tests/derive_debug.rs

@@ -523,6 +523,12 @@ fn declare_func(
 #[cfg(test)]
 mod tests {
     //! More tests can be found in src/codegen/codegen_tests.rs and its submodules.
+    //!
+    //! TODO: Gradually delete these tests and replace them with tests in the existing
+    //!  `mod codegen_tests`.
+    //!  This way we have one place to analyze the related Rust+Swift+C generated code
+    //!  vs. currently needing to look at `generate_swift.rs` `generate_c.rs` and `generate_rust.rs`
+    //!  to get a full picture of the codegen.
 
     use proc_macro2::TokenStream;
     use quote::quote;