Implement --version flag for cli (#53)

Co-authored-by: Natalie Weizenbaum <nweiz@google.com>

CHANGELOG.md

@@ -5,6 +5,9 @@
   * Emit colors as `Value.HslColor` if that internal representation is
     available.
 
+* Add a `--version` flag that will print a `VersionResponse` as JSON, for ease
+  of human identification.
+
 ## 1.0.0-beta.10
 
 * Support version 1.0.0-beta.12 of the Sass embedded protocol:

README.md

@@ -8,6 +8,11 @@ and importers.
 [Dart Sass]: https://sass-lang.com/dart-sass
 [Embedded Sass protocol]: https://github.com/sass/sass-embedded-protocol/blob/master/README.md#readme
 
+### Usage
+
+- `dart_sass_embedded` starts the compiler and listens on stdin.
+- `dart_sass_embedded --version` prints `versionResponse` with `id = 0` in JSON and exits.
+
 ### Releases
 
 Binary releases are available from the [GitHub release page]. We recommend that

bin/dart_sass_embedded.dart

@@ -19,6 +19,14 @@ import 'package:sass_embedded/src/utils.dart';
 
 void main(List<String> args) {
   if (args.isNotEmpty) {
+    if (args.first == "--version") {
+      var response = Dispatcher.versionResponse();
+      response.id = 0;
+      stdout.writeln(
+          JsonEncoder.withIndent("  ").convert(response.toProto3Json()));
+      return;
+    }
+
     stderr.writeln(
         "This executable is not intended to be executed with arguments.\n"
         "See https://github.com/sass/embedded-protocol#readme for details.");

lib/src/dispatcher.dart

@@ -57,16 +57,10 @@ class Dispatcher {
 
         switch (message.whichMessage()) {
           case InboundMessage_Message.versionRequest:
-            _send(OutboundMessage()
-              ..versionResponse = (OutboundMessage_VersionResponse()
-                ..protocolVersion =
-                    const String.fromEnvironment("protocol-version")
-                ..compilerVersion =
-                    const String.fromEnvironment("compiler-version")
-                ..implementationVersion =
-                    const String.fromEnvironment("implementation-version")
-                ..implementationName = "Dart Sass"
-                ..id = message.versionRequest.id));
+            var request = message.versionRequest;
+            var response = versionResponse();
+            response.id = request.id;
+            _send(OutboundMessage()..versionResponse = response);
             break;
 
           case InboundMessage_Message.compileRequest:
@@ -226,4 +220,14 @@ class Dispatcher {
         break;
     }
   }
+
+  /// Creates a [OutboundMessage_VersionResponse]
+  static OutboundMessage_VersionResponse versionResponse() {
+    return OutboundMessage_VersionResponse()
+      ..protocolVersion = const String.fromEnvironment("protocol-version")
+      ..compilerVersion = const String.fromEnvironment("compiler-version")
+      ..implementationVersion =
+          const String.fromEnvironment("implementation-version")
+      ..implementationName = "Dart Sass";
+  }
 }

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass_embedded
-version: 1.0.0-dev
+version: 1.0.0-beta.11
 description: An implementation of the Sass embedded protocol using Dart Sass.
 author: Sass Team
 homepage: https://github.com/sass/dart-sass-embedded