Test that clangd --check works at HEAD.

.ci.yaml

@@ -322,6 +322,12 @@ targets:
       - ci/**
       - flutter_frontend_server/**
 
+  - name: Linux clangd
+    recipe: engine_v2/engine_v2
+    bringup: true
+    properties:
+      config_name: linux_unopt_debug_no_rbe
+
   - name: Linux linux_unopt
     recipe: engine_v2/engine_v2
     timeout: 120
@@ -407,6 +413,12 @@ targets:
     drone_dimensions:
       - os=Mac-13
 
+  - name: Mac clangd
+    recipe: engine_v2/engine_v2
+    bringup: true
+    properties:
+      config_name: mac_unopt_debug_no_rbe
+
   - name: Mac mac_unopt
     recipe: engine_v2/engine_v2
     properties:

.clangd

@@ -0,0 +1,10 @@
+# Used to allow clangd to run on CI platforms as part of //tools/clangd_check.
+#
+# Intended to have no effect elsewhere.
+#
+# See also:
+# - https://clangd.llvm.org/config#compileflags
+# - https://github.com/clangd/clangd/issues/662
+CompileFlags:
+  Add: -Wno-unknown-warning-option
+  Remove: [-m*, -f*]

ci/builders/linux_unopt_debug_no_rbe.json

@@ -0,0 +1,32 @@
+{
+  "_comment": [
+    "This build is only used to generate compile_commands.json for clangd ",
+    "and should not be used for any other purpose."
+  ],
+  "builds": [
+    {
+      "drone_dimensions": ["device_type=none", "os=Linux", "cores=32"],
+      "gn": [
+        "--runtime-mode",
+        "debug",
+        "--unoptimized",
+        "--prebuilt-dart-sdk",
+        "--no-rbe",
+        "--no-goma"
+      ],
+      "name": "linux_unopt_debug_no_rbe",
+      "ninja": {
+        "config": "linux_unopt_debug_no_rbe",
+        "targets": ["flutter/build/dart:copy_dart_sdk"]
+      },
+      "tests": [
+        {
+          "language": "dart",
+          "name": "clangd",
+          "script": "flutter/tools/clangd_check/bin/main.dart",
+          "parameters": ["--clangd=buildtools/linux-x64/clang/bin/clangd"]
+        }
+      ]
+    }
+  ]
+}

ci/builders/mac_unopt_debug_no_rbe.json

@@ -0,0 +1,38 @@
+{
+  "_comment": [
+    "This build is only used to generate compile_commands.json for clangd ",
+    "and should not be used for any other purpose."
+  ],
+  "builds": [
+    {
+      "drone_dimensions": [
+        "device_type=none",
+        "os=Mac-13",
+        "cpu=x86",
+        "mac_model=Macmini8,1"
+      ],
+      "gn": [
+        "--runtime-mode",
+        "debug",
+        "--unoptimized",
+        "--prebuilt-dart-sdk",
+        "--no-rbe",
+        "--no-goma",
+        "--xcode-symlinks"
+      ],
+      "name": "mac_unopt_debug_no_rbe",
+      "ninja": {
+        "config": "mac_unopt_debug_no_rbe",
+        "targets": ["flutter/build/dart:copy_dart_sdk"]
+      },
+      "tests": [
+        {
+          "language": "dart",
+          "name": "clangd",
+          "script": "flutter/tools/clangd_check/bin/main.dart",
+          "parameters": ["--clangd=buildtools/mac-x64/clang/bin/clangd"]
+        }
+      ]
+    }
+  ]
+}

ci/licenses_golden/licenses_flutter

@@ -41990,6 +41990,7 @@ ORIGIN: ../../../flutter/vulkan/vulkan_utilities.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/vulkan/vulkan_window.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/vulkan/vulkan_window.h + ../../../flutter/LICENSE
 TYPE: LicenseType.bsd
+FILE: ../../../flutter/.clangd
 FILE: ../../../flutter/.pylintrc
 FILE: ../../../flutter/assets/asset_manager.cc
 FILE: ../../../flutter/assets/asset_manager.h

tools/clangd_check/README.md

@@ -0,0 +1,27 @@
+# `clangd_check`
+
+`clangd_check` is a tool to run clangd on a codebase and check for diagnostics.
+
+The practical use of this tool is intentionally limited; it's designed to
+provide a quick way to verify that `clangd` is able to parse and analyze a
+C++ codebase.
+
+## Usage
+
+```sh
+dart ./tools/clangd_check/bin/main.dart
+```
+
+On success, and with no diagnostics, `clangd_check` will exit with status 0.
+
+By default, `clangd_check` will try to infer the path of `clangd`, as well as
+the path to `--compile-commands-dir` based on what artifacts are present in
+`$ENGINE/src/out`.
+
+You can also specify the path to `clangd` and `--compile-commands-dir` manually:
+
+```sh
+dart ./tools/clangd_check/bin/main.dart \
+  --clangd ../buildtools/mac-arm64/clang/bin/clangd \
+  --compile-commands-dir ../out/host_Debug_unopt_arm64
+```

tools/clangd_check/bin/main.dart

@@ -0,0 +1,131 @@
+// Copyright 2013 The Flutter Authors. 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:convert';
+import 'dart:io' as io;
+
+import 'package:args/args.dart';
+import 'package:engine_repo_tools/engine_repo_tools.dart';
+import 'package:path/path.dart' as p;
+
+void main(List<String> args) {
+  final Engine? engine = Engine.tryFindWithin();
+  final ArgParser parser = ArgParser()
+    ..addFlag(
+      'help',
+      abbr: 'h',
+      help: 'Print this usage information.',
+      negatable: false,
+    )
+    ..addOption(
+      'clangd',
+      help: 'Path to clangd. Defaults to deriving the path from compile_commands.json.',
+    )
+    ..addOption(
+      'compile-commands-dir',
+      help: 'Path to a directory containing compile_commands.json.',
+      defaultsTo: engine?.latestOutput()?.compileCommandsJson.parent.path,
+    );
+  final ArgResults results = parser.parse(args);
+  if (results['help'] as bool) {
+    io.stdout.writeln(parser.usage);
+    return;
+  }
+
+  final String? compileCommandsDir = results['compile-commands-dir'] as String?;
+  if (compileCommandsDir == null) {
+    io.stderr.writeln('Must provide a path to compile_commands.json');
+    io.exitCode = 1;
+    return;
+  }
+  final io.File compileCommandsFile = io.File(p.join(compileCommandsDir, 'compile_commands.json'));
+  if (!compileCommandsFile.existsSync()) {
+    io.stderr.writeln('No compile_commands.json found in $compileCommandsDir');
+    io.exitCode = 1;
+    return;
+  }
+
+  final List<Object?> compileCommands = json.decode(compileCommandsFile.readAsStringSync()) as List<Object?>;
+  if (compileCommands.isEmpty) {
+    io.stderr.writeln('Unexpected: compile_commands.json is empty');
+    io.exitCode = 1;
+    return;
+  }
+
+  String? clangd = results['clangd'] as String?;
+  final Map<String, Object?> entry = compileCommands.first! as Map<String, Object?>;
+  final String checkFile;
+  if (entry case {
+    'command': final String command,
+    'file': final String file,
+  }) {
+    // Given a path like ../../flutter/foo.cc, we want to check foo.cc.
+    checkFile = p.split(file).skip(3).join(p.separator);
+    // On CI, the command path is different from the local path.
+    // Find the engine root and derive the clangd path from there.
+    if (clangd == null) {
+      // Strip the command to find the path to the engine root.
+      // i.e. "command": "/path/to/engine/src/... arg1 arg2 ..."
+      //
+      // This now looks like "../../flutter/buildtools/{platform}/{...}"
+      final String commandPath = p.dirname(command.split(' ').first);
+
+      // Find the canonical path to the command (i.e. resolve "../" and ".")
+      //
+      // This now looks like "/path/to/engine/src/flutter/buildtools/{platform}/{...}"
+      final String path = p.canonicalize(
+        p.join(compileCommandsDir, commandPath),
+      );
+
+      // Extract which platform we're building for (e.g. linux-x64, mac-arm64, mac-x64).
+      final String platform = RegExp(
+        r'buildtools/([^/]+)/',
+      ).firstMatch(path)!.group(1)!;
+
+      // Find the engine root and derive the clangd path from there.
+      final Engine compileCommandsEngineRoot = Engine.findWithin(path);
+      clangd = p.join(
+        // engine/src/flutter
+        compileCommandsEngineRoot.flutterDir.path,
+        // buildtools
+        'buildtools',
+        // {platform}
+        platform,
+        // clangd
+        'clang',
+        'bin',
+        'clangd',
+      );
+    }
+  } else {
+    io.stderr.writeln('Unexpected: compile_commands.json has an unexpected format');
+    io.stderr.writeln('First entry: ${const JsonEncoder.withIndent('  ').convert(entry)}');
+    io.exitCode = 1;
+    return;
+  }
+
+  // Run clangd.
+  try {
+    final io.ProcessResult result = io.Process.runSync(clangd, <String>[
+      '--compile-commands-dir',
+      compileCommandsDir,
+      '--check=$checkFile',
+    ]);
+    io.stdout.write(result.stdout);
+    io.stderr.write(result.stderr);
+    if ((result.stderr as String).contains('Path specified by --compile-commands-dir does not exist')) {
+      io.stdout.writeln('clangd_check failed: --compile-commands-dir does not exist');
+      io.exitCode = 1;
+    } else if ((result.stderr as String).contains('Failed to resolve path')) {
+      io.stdout.writeln('clangd_check failed: --check file does not exist');
+      io.exitCode = 1;
+    } else {
+      io.exitCode = result.exitCode;
+    }
+  } on io.ProcessException catch (e) {
+    io.stderr.writeln('Failed to run clangd: $e');
+    io.stderr.writeln(const JsonEncoder.withIndent('  ').convert(entry));
+    io.exitCode = 1;
+  }
+}

tools/clangd_check/pubspec.yaml

@@ -0,0 +1,68 @@
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+name: clangd_check
+publish_to: none
+
+# Do not add any dependencies that require more than what is provided in
+# //third_party/dart/pkg or //third_party/dart/third_party/pkg.
+# In particular, package:test is not usable here.
+
+# If you do add packages here, make sure you can run `pub get --offline`, and
+# check the .packages and .package_config to make sure all the paths are
+# relative to this directory into //third_party/dart
+
+environment:
+  sdk: '>=3.2.0-0 <4.0.0'
+
+dependencies:
+  args: any
+  engine_repo_tools: any
+  path: any
+  source_span: any
+
+dev_dependencies:
+  async_helper: any
+  expect: any
+  litetest: any
+  process_fakes: any
+  smith: any
+
+dependency_overrides:
+  args:
+    path: ../../../third_party/dart/third_party/pkg/args
+  async:
+    path: ../../../third_party/dart/third_party/pkg/async
+  async_helper:
+    path: ../../../third_party/dart/pkg/async_helper
+  collection:
+    path: ../../../third_party/dart/third_party/pkg/collection
+  engine_repo_tools:
+    path: ../pkg/engine_repo_tools
+  expect:
+    path: ../../../third_party/dart/pkg/expect
+  file:
+    path: ../../../third_party/dart/third_party/pkg/file/packages/file
+  git_repo_tools:
+    path: ../pkg/git_repo_tools
+  litetest:
+    path: ../../testing/litetest
+  meta:
+    path: ../../../third_party/dart/pkg/meta
+  path:
+    path: ../../../third_party/dart/third_party/pkg/path
+  platform:
+    path: ../../third_party/pkg/platform
+  process:
+    path: ../../third_party/pkg/process
+  process_fakes:
+    path: ../pkg/process_fakes
+  process_runner:
+    path: ../../third_party/pkg/process_runner
+  smith:
+    path: ../../../third_party/dart/pkg/smith
+  source_span:
+    path: ../../../third_party/dart/third_party/pkg/source_span
+  term_glyph:
+    path: ../../../third_party/dart/third_party/pkg/term_glyph

tools/pub_get_offline.py

@@ -34,6 +34,7 @@
     os.path.join(ENGINE_DIR, 'tools', 'api_check'),
     os.path.join(ENGINE_DIR, 'tools', 'build_bucket_golden_scraper'),
     os.path.join(ENGINE_DIR, 'tools', 'clang_tidy'),
+    os.path.join(ENGINE_DIR, 'tools', 'clangd_check'),
     os.path.join(ENGINE_DIR, 'tools', 'compare_goldens'),
     os.path.join(ENGINE_DIR, 'tools', 'const_finder'),
     os.path.join(ENGINE_DIR, 'tools', 'dir_contents_diff'),