Add libsignal-bridge-testing for Swift

Use a similar strategy as for Node, but with an additional crate that serves as 
the target for running cbindgen. The expectation is that since iOS links with 
the native signal_ffi statically, the linker will be able to prune out the 
unsued test-only code.

Cargo.lock

@@ -2097,6 +2097,7 @@ dependencies = [
  "cpufeatures",
  "futures-util",
  "libsignal-bridge",
+ "libsignal-bridge-testing",
  "libsignal-net",
  "libsignal-protocol",
  "log",

rust/bridge/ffi/Cargo.toml

@@ -22,6 +22,7 @@ testing-fns = ["libsignal-bridge/testing-fns"]
 
 [dependencies]
 libsignal-bridge = { path = "../shared", features = ["ffi"] }
+libsignal-bridge-testing = { path = "../shared/testing", features = ["ffi"] }
 libsignal-net = { path = "../../net" }
 libsignal-protocol = { path = "../../protocol" }
 signal-media = { path = "../../media" }

rust/bridge/ffi/cbindgen-testing.toml

@@ -0,0 +1,59 @@
+#
+# Copyright (C) 2024 Signal Messenger, LLC.
+# SPDX-License-Identifier: AGPL-3.0-only
+#
+
+language = "C"
+
+header = "/*\nCopyright (C) 2024 Signal Messenger, LLC.\nSPDX-License-Identifier: AGPL-3.0-only\n*/\n"
+
+include_guard = "SIGNAL_FFI_TESTING_H_"
+
+autogen_warning = "/* This file was automatically generated by cbindgen */"
+
+includes = ["signal_ffi.h"]
+
+style = "type"
+
+usize_is_size_t = true
+
+[defines]
+"feature = signal-media" = "SIGNAL_MEDIA_SUPPORTED"
+
+[enum]
+prefix_with_name = true
+
+[export]
+exclude = ["TAG_SIZE", "NONCE_SIZE"]
+item_types = [
+    "enums",
+    "functions",
+    "opaque",
+    "structs",
+    "typedefs",
+    "constants",
+]
+# FIXME: this doesn't work well with constants in SCREAMING_SNAKE_CASE
+prefix = "Signal"
+renaming_overrides_prefixing = true
+
+[export.rename]
+# Avoid double-prefixing these
+"SignalFfiError" = "SignalFfiError"
+"SignalErrorCode" = "SignalErrorCode"
+
+[export.mangle]
+remove_underscores = true
+
+[fn]
+sort_by = "None"
+args = "horizontal"
+
+[parse]
+parse_deps = true
+include = []
+extra_bindings = ["libsignal-bridge-testing"]
+
+[parse.expand]
+crates = ["libsignal-bridge-testing"]
+features = ["libsignal-bridge-testing/ffi"]

rust/bridge/ffi/src/lib.rs

@@ -8,6 +8,8 @@
 
 use futures_util::FutureExt;
 use libsignal_bridge::ffi::*;
+#[allow(unused_imports)]
+use libsignal_bridge_testing::*;
 use libsignal_protocol::*;
 
 use std::ffi::{c_char, c_uchar, c_uint, CString};

swift/Sources/SignalFfi/module.modulemap

@@ -4,5 +4,6 @@
 //
 module SignalFfi {
 	header "signal_ffi.h"
+	header "signal_ffi_testing.h"
 	link "signal_ffi"
 }

swift/Sources/SignalFfi/signal_ffi_testing.h

@@ -0,0 +1,21 @@
+/*
+Copyright (C) 2024 Signal Messenger, LLC.
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+
+#ifndef SIGNAL_FFI_TESTING_H_
+#define SIGNAL_FFI_TESTING_H_
+
+/* This file was automatically generated by cbindgen */
+
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include "signal_ffi.h"
+
+SignalFfiError *signal_test_only_fn_returns_123(uint32_t *out);
+
+#endif /* SIGNAL_FFI_TESTING_H_ */

swift/Tests/LibSignalClientTests/NativeTests.swift

@@ -0,0 +1,16 @@
+//
+// Copyright 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+import Foundation
+@testable import LibSignalClient
+import SignalFfi
+import XCTest
+
+final class NativeTests: XCTestCase {
+    func testTestingFnsAreAvailable() async throws {
+        let output = try invokeFnReturningInteger(fn: SignalFfi.signal_test_only_fn_returns_123)
+        XCTAssertEqual(output, 123)
+    }
+}

swift/build_ffi.sh

@@ -134,6 +134,7 @@ fi
 echo_then_run cargo build -p libsignal-ffi ${RELEASE_BUILD:+--release} ${VERBOSE:+--verbose} ${CARGO_BUILD_TARGET:+--target $CARGO_BUILD_TARGET} ${FEATURES:+--features "${FEATURES[*]}"} ${BUILD_STD:+-Zbuild-std}
 
 FFI_HEADER_PATH=swift/Sources/SignalFfi/signal_ffi.h
+FFI_TESTING_HEADER_PATH=swift/Sources/SignalFfi/signal_ffi_testing.h
 
 if [[ -n "${SHOULD_CBINDGEN}" ]]; then
   check_cbindgen
@@ -145,6 +146,12 @@ if [[ -n "${SHOULD_CBINDGEN}" ]]; then
       echo 'error: signal_ffi.h not up to date; run' "$0" '--generate-ffi' >&2
       exit 1
     fi
+    echo diff -u "${FFI_TESTING_HEADER_PATH}" "<(cbindgen -q ${RELEASE_BUILD:+--profile release} rust/bridge/shared/testing --config rust/bridge/ffi/cbindgen-testing.toml)"
+    if ! diff -u "${FFI_TESTING_HEADER_PATH}"  <(cbindgen -q ${RELEASE_BUILD:+--profile release} rust/bridge/shared/testing --config rust/bridge/ffi/cbindgen-testing.toml); then
+      echo
+      echo 'error: signal_ffi_testing.h not up to date; run' "$0" '--generate-ffi' >&2
+      exit 1
+    fi
   else
     echo cbindgen ${RELEASE_BUILD:+--profile release} -o "${FFI_HEADER_PATH}" rust/bridge/ffi
     # Use sed to ignore irrelevant cbindgen warnings.
@@ -152,5 +159,10 @@ if [[ -n "${SHOULD_CBINDGEN}" ]]; then
     # shellcheck disable=SC2016
     cbindgen ${RELEASE_BUILD:+--profile release} -o "${FFI_HEADER_PATH}" rust/bridge/ffi 2>&1 |
       sed '/WARN: Missing `\[defines\]` entry for `feature = "ffi"` in cbindgen config\./ d' >&2
+
+    echo cbindgen ${RELEASE_BUILD:+--profile release} -o "${FFI_TESTING_HEADER_PATH}" rust/bridge/shared/testing --config rust/bridge/ffi/cbindgen-testing.toml
+    # shellcheck disable=SC2016
+    cbindgen ${RELEASE_BUILD:+--profile release} -o "${FFI_TESTING_HEADER_PATH}" rust/bridge/shared/testing --config rust/bridge/ffi/cbindgen-testing.toml 2>&1 |
+      sed '/WARN: Missing `\[defines\]` entry for `feature = "ffi"` in cbindgen config\./ d' >&2
   fi
 fi