locating runtime files automatically (fixes #96)

lib/src/options.dart

Index: lib/src/options.dart
diff --git a/lib/src/options.dart b/lib/src/options.dart
index 968ce65508ade5a00632b97e71c320b819f09411..238dafa74180c63a47300da2df84a6ee126b8aa0 100644
--- a/lib/src/options.dart
+++ b/lib/src/options.dart
@@ -11,6 +11,8 @@ import 'package:args/args.dart';
 import 'package:cli_util/cli_util.dart' show getSdkDir;
 import 'package:dev_compiler/config.dart';
 import 'package:logging/logging.dart' show Level;
+import 'package:path/path.dart' as path;
+import 'package:yaml/yaml.dart';
 
 /// Options used by our TypeResolver.
 class ResolverOptions {
@@ -191,6 +193,11 @@ class CompilerOptions implements RulesOptions, ResolverOptions, JSCodeOptions {
   @override
   final bool emitSourceMaps;
 
+  /// Location for runtime files, such as `dart_core.js`. By default this is
+  /// inferred to be under `lib/runtime/` in the location of the `dev_compiler`
+  /// package (if we can infer where that is located).
+  final String runtimeDir;
+
   CompilerOptions({this.allowConstCasts: true, this.checkSdk: false,
       this.dumpInfo: false, this.dumpInfoFile, this.dumpSrcDir,
       this.forceCompile: false, this.formatOutput: false,
@@ -205,7 +212,7 @@ class CompilerOptions implements RulesOptions, ResolverOptions, JSCodeOptions {
       this.nonnullableTypes: TypeOptions.NONNULLABLE_TYPES, this.help: false,
       this.useMockSdk: false, this.dartSdkPath, this.logLevel: Level.SEVERE,
       this.emitSourceMaps: true, this.entryPointFile: null,
-      this.serverMode: false, this.port: 8080});
+      this.serverMode: false, this.port: 8080, this.runtimeDir});
 }
 
 /// Parses options from the command-line
@@ -217,6 +224,10 @@ CompilerOptions parseOptions(List<String> argv) {
   if (sdkPath == null && !args['mock-sdk']) {
     sdkPath = getSdkDir(argv).path;
   }
+  var runtimeDir = args['runtime-dir'];
+  if (runtimeDir == null) {
+    runtimeDir = _computeRuntimeDir();
+  }
   return new CompilerOptions(
       allowConstCasts: args['allow-const-casts'],
       checkSdk: args['sdk-check'],
@@ -247,7 +258,8 @@ CompilerOptions parseOptions(List<String> argv) {
       emitSourceMaps: args['source-maps'],
       entryPointFile: args.rest.length == 0 ? null : args.rest.first,
       serverMode: args['server'],
-      port: int.parse(args['port']));
+      port: int.parse(args['port']),
+      runtimeDir: runtimeDir);
 }
 
 final ArgParser argParser = new ArgParser()
@@ -298,6 +310,8 @@ final ArgParser argParser = new ArgParser()
       'the list of directories where to look for packages.', defaultsTo: '')
   ..addFlag('source-maps',
       help: 'Whether to emit source map files', defaultsTo: true)
+  ..addOption('runtime-dir',
+      help: 'Where to find dev_compiler\'s runtime files', defaultsTo: null)
 
   // general options
   ..addFlag('help', abbr: 'h', help: 'Display this message')
@@ -314,3 +328,54 @@ final ArgParser argParser = new ArgParser()
       abbr: 'f',
       help: 'Dump info json file (requires dump-info)',
       defaultsTo: null);
+
+/// Tries to find the `lib/runtime/` directory of the dev_compiler package. This
+/// works when running devc from it's sources or from a snapshot that is
+/// activated via `pub global activate`.
+String _computeRuntimeDir() {
+  var scriptUri = Platform.script;
+  var scriptPath = scriptUri.path;
+  var file = path.basename(scriptPath);
+  var dir = path.dirname(scriptPath);
+  var lastdir = path.basename(dir);
+  dir = path.dirname(dir);
+
+  // Both the source devc.dart and the snapshot generated by pub global activate
+  // are under a bin folder.
+  if (lastdir != 'bin') return null;
+
+  // And both under a project directory containing a pubspec.lock file.
+  var lockfile = path.join(dir, 'pubspec.lock');
+  if (!new File(lockfile).existsSync()) return null;
+
+  // If running from sources we found it!
+  if (file == 'devc.dart') return path.join(dir, 'lib', 'runtime');
+
+  // If running from a pub global snapshot, we need to read the lock file to
+  // find where the actual sources are located in the pub cache.
+  if (file == 'devc.dart.snapshot') {
+    // Note: this depends on implementation details of pub.
+    var yaml = loadYaml(new File(lockfile).readAsStringSync());
+    var info = yaml['packages']['dev_compiler'];
+    if (info == null) return null;
+
+    var cacheDir;
+    if (info['source'] == 'hosted') {
+      cacheDir = path.join(
+          'hosted', 'pub.dartlang.org', 'dev_compiler-${info["version"]}');
+    } else if (info['source'] == 'git') {
+      var ref = info['description']['resolved-ref'];
+      cacheDir = path.join('git', 'dev_compiler-${ref}');
+    }
+
+    // We should be under "/path/to/pub-cache/global_packages/dev_compiler".
+    // The pub-cache directory is two levels up, but we verify that the layout
+    // looks correct.
+    if (path.basename(dir) != 'dev_compiler') return null;
+    dir = path.dirname(dir);
+    if (path.basename(dir) != 'global_packages') return null;
+    dir = path.dirname(dir);
+    return path.join(dir, cacheDir, 'lib', 'runtime');
+  }
+  return null;
+}