Test that clangd --check works at HEAD.

ci/builders/linux_unopt.json

@@ -79,6 +79,11 @@
                         "flutter/shell/testing/observatory/empty_main.dart"
                     ]
                 },
+                {
+                    "language": "dart",
+                    "name": "test: clangd",
+                    "script": "flutter/tools/clangd_check/bin/main.dart"
+                },
                 {
                     "language": "dart",
                     "name": "test: Lint android host",

ci/builders/mac_unopt.json

@@ -273,6 +273,11 @@
                         "ios_debug_unopt_sim_arm64_extension_safe"
                     ],
                     "script": "flutter/testing/scenario_app/run_ios_tests.sh"
+                },
+                {
+                    "language": "dart",
+                    "name": "test: clangd",
+                    "script": "flutter/tools/clangd_check/bin/main.dart"
                 }
             ]
         }

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 +1,75 @@
+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()
+    ..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);
+
+  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 path,
+    'file': final String file,
+  }) {
+    checkFile = p.split(file).skip(3).join(p.separator);
+    clangd ??= p.join(p.dirname(p.dirname(path.split(' ').first)), 'clang', 'bin', 'clangd');
+  } else {
+    io.stderr.writeln('Unexpected: compile_commands.json has an unexpected format');
+    io.stderr.writeln('First entry: ${const JsonEncoder.withIndent('  ').convert(entry)}');
+    io.exitCode = 1;
+    return;
+  }
+
+  // Run clangd.
+  final io.ProcessResult result = io.Process.runSync(clangd, <String>[
+    '--compile-commands-dir',
+    compileCommandsDir,
+    '--check=$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;
+  }
+}

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'),