[native_toolchain_c] Fix treeshaking on mac (#2399)

By creating a list of symbols to be exported. 

Also needs to be tested with ICU4X, but manually setting this seems to do the trick to solve dart-lang/i18n#989

---

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  <summary>Contribution guidelines:</summary><br>

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</details>

Author: mosuem

.github/workflows/native_toolchain_c.yaml

@@ -47,6 +47,9 @@ jobs:
       - name: Install native toolchains
         run: sudo apt-get update && sudo apt-get install gcc-i686-linux-gnu gcc-aarch64-linux-gnu gcc-arm-linux-gnueabihf gcc-riscv64-linux-gnu
 
+      - name: Install rust for pkgs/native_toolchain_c/test/clinker/rust_test.dart
+        uses: actions-rust-lang/setup-rust-toolchain@fb51252c7ba57d633bc668f941da052e410add48
+
       - run: git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
       - run: echo "$PWD/depot_tools" >> $GITHUB_PATH
       - run: mkdir dart-sdk

.github/workflows/publish.yaml

@@ -25,3 +25,4 @@ jobs:
     with:
       write-comments: false
       sdk: dev # use beta/stable after 3.3.0
+      ignore-packages: pkgs/objective_c,pkgs/ffigen,pkgs/jni,pkgs/jnigen

pkgs/hooks_runner/test_data/treeshaking_native_libs/hook/link.dart

@@ -12,7 +12,7 @@ void main(List<String> arguments) async {
     final linker = CLinker.library(
       name: input.packageName,
       assetName: input.assets.code.single.id.split('/').skip(1).join('/'),
-      linkerOptions: LinkerOptions.treeshake(symbols: ['add']),
+      linkerOptions: LinkerOptions.treeshake(symbolsToKeep: ['add']),
       sources: [input.assets.code.single.file!.toFilePath()],
     );
     await linker.run(

pkgs/native_toolchain_c/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.17.0
+
+* Fix treeshaking on mac.
+
 ## 0.16.8
 
 * Support building assets for packages which are not the input package.

pkgs/native_toolchain_c/lib/src/cbuilder/linker_options.dart

@@ -25,45 +25,48 @@ class LinkerOptions {
   /// See also the `ld` man page at https://linux.die.net/man/1/ld.
   final bool gcSections;
 
-  /// The linker script to be passed via `--version-script`.
-  ///
-  /// See also the `ld` man page at https://linux.die.net/man/1/ld.
-  final Uri? linkerScript;
+  final LinkerScriptMode? _linkerScriptMode;
 
   /// Whether to strip debugging symbols from the binary.
   final bool stripDebug;
 
   /// The symbols to keep in the resulting binaries.
-  ///
-  /// If null all symbols will be kept.
-  final List<String>? _symbolsToKeep;
+  final List<String> _symbols;
 
-  final bool _generateLinkerScript;
+  final bool _keepAllSymbols;
 
   /// Create linking options manually for fine-grained control.
+  ///
+  /// If [symbolsToKeep] is null, all symbols will be kept.
   LinkerOptions.manual({
     List<String>? flags,
     bool? gcSections,
-    this.linkerScript,
+    Uri? linkerScript,
     this.stripDebug = true,
     Iterable<String>? symbolsToKeep,
   }) : _linkerFlags = flags ?? [],
        gcSections = gcSections ?? true,
-       _symbolsToKeep = symbolsToKeep?.toList(growable: false),
-       _generateLinkerScript = false;
+       _symbols = symbolsToKeep?.toList(growable: false) ?? const [],
+       _keepAllSymbols = symbolsToKeep == null,
+       _linkerScriptMode = linkerScript != null
+           ? ManualLinkerScript(script: linkerScript)
+           : null;
 
   /// Create linking options to tree-shake symbols from the input files.
   ///
-  /// The [symbols] specify the symbols which should be kept.
+  /// The [symbolsToKeep] specify the symbols which should be kept. Passing
+  /// `null` implies that all symbols should be kept.
   LinkerOptions.treeshake({
     Iterable<String>? flags,
-    required Iterable<String>? symbols,
+    required Iterable<String>? symbolsToKeep,
     this.stripDebug = true,
   }) : _linkerFlags = flags?.toList(growable: false) ?? [],
-       _symbolsToKeep = symbols?.toList(growable: false),
+       _symbols = symbolsToKeep?.toList(growable: false) ?? const [],
+       _keepAllSymbols = symbolsToKeep == null,
        gcSections = true,
-       linkerScript = null,
-       _generateLinkerScript = symbols != null;
+       _linkerScriptMode = symbolsToKeep != null
+           ? GenerateLinkerScript()
+           : null;
 
   Iterable<String> _toLinkerSyntax(Tool linker, Iterable<String> flagList) {
     if (linker.isClangLike) {
@@ -76,6 +79,19 @@ class LinkerOptions {
   }
 }
 
+sealed class LinkerScriptMode {}
+
+final class GenerateLinkerScript extends LinkerScriptMode {}
+
+final class ManualLinkerScript extends LinkerScriptMode {
+  /// The linker script to be passed via `--version-script`.
+  ///
+  /// See also the `ld` man page at https://linux.die.net/man/1/ld.
+  final Uri script;
+
+  ManualLinkerScript({required this.script});
+}
+
 extension LinkerOptionsExt on LinkerOptions {
   /// Takes [sourceFiles] and turns it into flags for the compiler driver while
   /// considering the current [LinkerOptions].
@@ -99,8 +115,6 @@ extension LinkerOptionsExt on LinkerOptions {
     }
   }
 
-  bool get _includeAllSymbols => _symbolsToKeep == null;
-
   Iterable<String> _sourceFilesToFlagsForClangLike(
     Tool tool,
     Iterable<String> sourceFiles,
@@ -109,33 +123,37 @@ extension LinkerOptionsExt on LinkerOptions {
     switch (targetOS) {
       case OS.macOS || OS.iOS:
         return [
-          if (!_includeAllSymbols) ...sourceFiles,
+          if (!_keepAllSymbols) ...sourceFiles,
           ..._toLinkerSyntax(tool, [
-            if (_includeAllSymbols) ...sourceFiles.map((e) => '-force_load,$e'),
+            if (_keepAllSymbols) ...sourceFiles.map((e) => '-force_load,$e'),
             ..._linkerFlags,
-            ..._symbolsToKeep?.map((symbol) => '-u,_$symbol') ?? [],
+            ..._symbols.map((symbol) => '-u,_$symbol'),
             if (stripDebug) '-S',
             if (gcSections) '-dead_strip',
+            if (_linkerScriptMode is ManualLinkerScript)
+              '-exported_symbols_list,${_linkerScriptMode.script.toFilePath()}'
+            else if (_linkerScriptMode is GenerateLinkerScript)
+              '-exported_symbols_list,${_createMacSymbolList(_symbols)}',
           ]),
         ];
 
       case OS.android || OS.linux:
         final wholeArchiveSandwich =
             sourceFiles.any((source) => source.endsWith('.a')) ||
-            _includeAllSymbols;
+            _keepAllSymbols;
         return [
           if (wholeArchiveSandwich)
             ..._toLinkerSyntax(tool, ['--whole-archive']),
           ...sourceFiles,
           ..._toLinkerSyntax(tool, [
             ..._linkerFlags,
-            ..._symbolsToKeep?.map((symbol) => '-u,$symbol') ?? [],
+            ..._symbols.map((symbol) => '-u,$symbol'),
             if (stripDebug) '--strip-debug',
             if (gcSections) '--gc-sections',
-            if (linkerScript != null)
-              '--version-script=${linkerScript!.toFilePath()}'
-            else if (_generateLinkerScript && _symbolsToKeep != null)
-              '--version-script=${_createClangLikeLinkScript(_symbolsToKeep)}',
+            if (_linkerScriptMode is ManualLinkerScript)
+              '--version-script=${_linkerScriptMode.script.toFilePath()}'
+            else if (_linkerScriptMode is GenerateLinkerScript)
+              '--version-script=${_createClangLikeLinkScript(_symbols)}',
             if (wholeArchiveSandwich) '--no-whole-archive',
           ]),
         ];
@@ -152,21 +170,34 @@ extension LinkerOptionsExt on LinkerOptions {
   ) => [
     ...sourceFiles,
     '/link',
-    if (_includeAllSymbols) ...sourceFiles.map((e) => '/WHOLEARCHIVE:$e'),
+    if (_keepAllSymbols) ...sourceFiles.map((e) => '/WHOLEARCHIVE:$e'),
     ..._linkerFlags,
-    ..._symbolsToKeep?.map(
-          (symbol) =>
-              '/INCLUDE:${targetArch == Architecture.ia32 ? '_' : ''}$symbol',
-        ) ??
-        [],
-    if (linkerScript != null)
-      '/DEF:${linkerScript!.toFilePath()}'
-    else if (_generateLinkerScript && _symbolsToKeep != null)
-      '/DEF:${_createClLinkScript(_symbolsToKeep)}',
+    ..._symbols.map(
+      (symbol) =>
+          '/INCLUDE:${targetArch == Architecture.ia32 ? '_' : ''}$symbol',
+    ),
+    if (_linkerScriptMode is ManualLinkerScript)
+      '/DEF:${_linkerScriptMode.script.toFilePath()}'
+    else if (_linkerScriptMode is GenerateLinkerScript)
+      '/DEF:${_createClLinkScript(_symbols)}',
     if (stripDebug) '/PDBSTRIPPED',
     if (gcSections) '/OPT:REF',
   ];
 
+  /// This creates a list of exported symbols.
+  ///
+  /// If this is not set, some symbols might be kept. This can be inspected
+  /// using `ld -why_live`, see https://www.unix.com/man_page/osx/1/ld/, where
+  /// the reason will show up as `global-dont-strip`.
+  /// This might possibly be a Rust only feature.
+  static String _createMacSymbolList(Iterable<String> symbols) {
+    final tempDir = Directory.systemTemp.createTempSync();
+    final symbolsFileUri = tempDir.uri.resolve('exported_symbols_list.txt');
+    final symbolsFile = File.fromUri(symbolsFileUri)..createSync();
+    symbolsFile.writeAsStringSync(symbols.map((e) => '_$e').join('\n'));
+    return symbolsFileUri.toFilePath();
+  }
+
   static String _createClangLikeLinkScript(Iterable<String> symbols) {
     final tempDir = Directory.systemTemp.createTempSync();
     final symbolsFileUri = tempDir.uri.resolve('symbols.lds');

pkgs/native_toolchain_c/pubspec.yaml

@@ -1,7 +1,7 @@
 name: native_toolchain_c
 description: >-
   A library to invoke the native C compiler installed on the host machine.
-version: 0.16.8
+version: 0.17.0
 repository: https://github.com/dart-lang/native/tree/main/pkgs/native_toolchain_c
 
 topics:

pkgs/native_toolchain_c/test/clinker/rust_test.dart

@@ -0,0 +1,123 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:code_assets/code_assets.dart';
+import 'package:hooks/hooks.dart';
+import 'package:native_toolchain_c/native_toolchain_c.dart';
+import 'package:test/test.dart';
+
+import '../helpers.dart';
+
+Future<void> main() async {
+  late final LinkInput linkInput;
+  late final Uri staticLib;
+  final linkOutputBuilder = LinkOutputBuilder();
+  final targetArchitecture = Architecture.current;
+  final targetOS = OS.current;
+  late final bool rustToolchainInstalled;
+  setUpAll(() async {
+    final tempUri = await tempDirForTest();
+    final tempUri2 = await tempDirForTest();
+    staticLib = tempUri.resolve(targetOS.staticlibFileName('libtest'));
+    final processResult = await Process.run('rustc', [
+      '--crate-type=staticlib',
+      'test/clinker/testfiles/linker/test.rs',
+      '-o',
+      staticLib.toFilePath(),
+    ]);
+    rustToolchainInstalled = processResult.exitCode == 0;
+    if (rustToolchainInstalled) {
+      await File.fromUri(
+        staticLib,
+      ).copy(tempUri.resolve('libtest.a').toFilePath());
+    }
+    final linkInputBuilder = LinkInputBuilder()
+      ..setupShared(
+        packageName: 'testpackage',
+        packageRoot: tempUri,
+        outputFile: tempUri.resolve('output.json'),
+        outputDirectoryShared: tempUri2,
+      )
+      ..setupLink(assets: [], recordedUsesFile: null)
+      ..addExtension(
+        CodeAssetExtension(
+          targetOS: targetOS,
+          targetArchitecture: targetArchitecture,
+          linkModePreference: LinkModePreference.dynamic,
+        ),
+      );
+
+    linkInput = linkInputBuilder.build();
+  });
+  test('link rust binary with script treeshakes', () async {
+    if (!rustToolchainInstalled) {
+      return;
+    }
+    final treeshakeOption = LinkerOptions.treeshake(
+      symbolsToKeep: ['my_other_func'],
+    );
+    final symbols = await _link(
+      staticLib,
+      treeshakeOption,
+      linkInput,
+      linkOutputBuilder,
+      targetArchitecture,
+      targetOS,
+    );
+    final skipReason = symbols == null
+        ? 'tool to extract symbols unavailable'
+        : false;
+    expect(symbols, contains('my_other_func'), skip: skipReason);
+    expect(symbols, isNot(contains('my_func')), skip: skipReason);
+  });
+
+  test('link rust binary without script keeps symbols', () async {
+    if (!rustToolchainInstalled) {
+      return;
+    }
+    final manualOption = LinkerOptions.manual(
+      symbolsToKeep: ['my_other_func'],
+      stripDebug: true,
+      gcSections: true,
+    );
+    final symbols = await _link(
+      staticLib,
+      manualOption,
+      linkInput,
+      linkOutputBuilder,
+      targetArchitecture,
+      targetOS,
+    );
+    final skipReason = symbols == null
+        ? 'tool to extract symbols unavailable'
+        : false;
+    expect(symbols, contains('my_other_func'), skip: skipReason);
+    expect(symbols, contains('my_func'), skip: skipReason);
+  });
+}
+
+Future<String?> _link(
+  Uri staticLib,
+  LinkerOptions manualOption,
+  LinkInput linkInput,
+  LinkOutputBuilder linkOutputBuilder,
+  Architecture targetArchitecture,
+  OS targetOS,
+) async {
+  await CLinker.library(
+    name: 'mylibname',
+    assetName: '',
+    sources: [staticLib.toFilePath()],
+    linkerOptions: manualOption,
+  ).run(input: linkInput, output: linkOutputBuilder, logger: logger);
+
+  final linkOutput = linkOutputBuilder.build();
+  final asset = linkOutput.assets.code.first;
+
+  await expectMachineArchitecture(asset.file!, targetArchitecture, targetOS);
+
+  return await readSymbols(asset, targetOS);
+}

pkgs/native_toolchain_c/test/clinker/testfiles/linker/symbols.txt

@@ -0,0 +1 @@
+_my_other_func

pkgs/native_toolchain_c/test/clinker/testfiles/linker/test.rs

@@ -0,0 +1,9 @@
+#[no_mangle]
+pub extern "C" fn my_func() -> u64 {
+    return 41;
+}
+
+#[no_mangle]
+pub extern "C" fn my_other_func() -> u64 {
+    return 42;
+}