Support package: URLs as a Dart library (#53)

lib/sass.dart

@@ -5,7 +5,7 @@
 import 'package:path/path.dart' as p;
 
 import 'src/ast/sass.dart';
-import 'src/exception.dart';
+import 'src/sync_package_resolver.dart';
 import 'src/utils.dart';
 import 'src/visitor/perform.dart';
 import 'src/visitor/serialize.dart';
@@ -14,13 +14,21 @@ import 'src/visitor/serialize.dart';
 ///
 /// If [color] is `true`, this will use terminal colors in warnings.
 ///
-/// Throws a [SassException] if conversion fails.
-String render(String path, {bool color: false}) {
+/// If [packageResolver] is provided, it's used to resolve `package:` imports.
+/// Otherwise, they aren't supported. It takes a [SyncPackageResolver][] from
+/// the `package_resolver` package.
+///
+/// [SyncPackageResolver]: https://www.dartdocs.org/documentation/package_resolver/latest/package_resolver/SyncPackageResolver-class.html
+///
+/// Finally throws a [SassException] if conversion fails.
+String render(String path,
+    {bool color: false, SyncPackageResolver packageResolver}) {
   var contents = readSassFile(path);
   var url = p.toUri(path);
   var sassTree = p.extension(path) == '.sass'
       ? new Stylesheet.parseSass(contents, url: url, color: color)
       : new Stylesheet.parseScss(contents, url: url, color: color);
-  var cssTree = evaluate(sassTree, color: color);
+  var cssTree =
+      evaluate(sassTree, color: color, packageResolver: packageResolver);
   return toCss(cssTree);
 }

lib/src/io/interface.dart

@@ -37,5 +37,8 @@ String readFileAsString(String path) => null;
 /// Returns whether a file at [path] exists.
 bool fileExists(String path) => null;
 
+/// Returns whether a dir at [path] exists.
+bool dirExists(String path) => null;
+
 /// Gets and sets the exit code that the process will use when it exits.
 int exitCode;

lib/src/io/node.dart

@@ -74,6 +74,8 @@ String _cleanErrorMessage(_SystemError error) {
 
 bool fileExists(String path) => _fs.existsSync(path);
 
+bool dirExists(String path) => _fs.existsSync(path);
+
 @JS("process.stderr")
 external _Stderr get _stderr;
 

lib/src/io/vm.dart

@@ -15,3 +15,5 @@ List<int> readFileAsBytes(String path) => new io.File(path).readAsBytesSync();
 String readFileAsString(String path) => new io.File(path).readAsStringSync();
 
 bool fileExists(String path) => new io.File(path).existsSync();
+
+bool dirExists(String path) => new io.Directory(path).existsSync();

lib/src/sync_package_resolver.dart

@@ -0,0 +1,2 @@
+export 'package:package_resolver/package_resolver.dart'
+    if (node) 'sync_package_resolver/node.dart';

lib/src/sync_package_resolver/node.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2016, 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:async';
+
+class SyncPackageResolver {
+  static final _error =
+      new UnsupportedError('SyncPackageResolver is not supported in JS.');
+
+  static Future<SyncPackageResolver> get current => throw _error;
+
+  Uri resolveUri(packageUri) => throw _error;
+
+  factory SyncPackageResolver.config(Map<String, Uri> configMap) =>
+      throw _error;
+}

lib/src/visitor/perform.dart

@@ -21,6 +21,7 @@ import '../exception.dart';
 import '../extend/extender.dart';
 import '../io.dart';
 import '../parse/keyframe_selector.dart';
+import '../sync_package_resolver.dart';
 import '../utils.dart';
 import '../value.dart';
 import 'interface/statement.dart';
@@ -43,9 +44,13 @@ typedef _ScopeCallback(callback());
 CssStylesheet evaluate(Stylesheet stylesheet,
         {Iterable<String> loadPaths,
         Environment environment,
-        bool color: false}) =>
+        bool color: false,
+        SyncPackageResolver packageResolver}) =>
     new _PerformVisitor(
-            loadPaths: loadPaths, environment: environment, color: color)
+            loadPaths: loadPaths,
+            environment: environment,
+            color: color,
+            packageResolver: packageResolver)
         .run(stylesheet);
 
 /// A visitor that executes Sass code to produce a CSS tree.
@@ -131,11 +136,18 @@ class _PerformVisitor
   /// invocations, and imports surrounding the current context.
   final _stack = <Frame>[];
 
+  /// The resolver to use for `package:` URLs, or `null` if no resolver exists.
+  final SyncPackageResolver _packageResolver;
+
   _PerformVisitor(
-      {Iterable<String> loadPaths, Environment environment, bool color: false})
+      {Iterable<String> loadPaths,
+      Environment environment,
+      bool color: false,
+      SyncPackageResolver packageResolver})
       : _loadPaths = loadPaths == null ? const [] : new List.from(loadPaths),
         _environment = environment ?? new Environment(),
-        _color = color {
+        _color = color,
+        _packageResolver = packageResolver {
     _environment.defineFunction("variable-exists", r"$name", (arguments) {
       var variable = arguments[0].assertString("name");
       return new SassBoolean(_environment.variableExists(variable.text));
@@ -581,11 +593,27 @@ class _PerformVisitor
     _activeImports.remove(url);
   }
 
+  /// Returns [import]'s URL, resolved to a `file:` URL if possible.
+  Uri _resolveImportUrl(DynamicImport import) {
+    var packageUrl = import.url;
+    if (packageUrl.scheme != 'package') return packageUrl;
+
+    if (_packageResolver == null) {
+      throw _exception(
+          '"package:" URLs aren\'t supported on this platform.', import.span);
+    }
+
+    var resolvedPackageUrl = _packageResolver.resolveUri(packageUrl);
+    if (resolvedPackageUrl != null) return resolvedPackageUrl;
+
+    throw _exception("Unknown package.", import.span);
+  }
+
   /// Loads the [Stylesheet] imported by [import], or throws a
   /// [SassRuntimeException] if loading fails.
   Stylesheet _loadImport(DynamicImport import) {
     var path = _importPaths.putIfAbsent(import, () {
-      var path = p.fromUri(import.url);
+      var path = p.fromUri(_resolveImportUrl(import));
       var extension = p.extension(path);
       var tryPath = extension == '.sass' || extension == '.scss'
           ? _tryImportPath

pubspec.yaml

@@ -19,6 +19,7 @@ dependencies:
   string_scanner: ">=0.1.5 <2.0.0"
   stack_trace: ">=0.9.0 <2.0.0"
   tuple: "^1.0.0"
+  package_resolver: ^1.0.0
 
 dev_dependencies:
   archive: "^1.0.0"

test/cli_shared.dart

@@ -95,4 +95,17 @@ void sharedTests(ScheduledProcess runSass(List arguments)) {
     sass.stderr.expect(consumeThrough(contains("\.dart")));
     sass.shouldExit(65);
   });
+
+  test("fails to import a package url", () {
+    d.file("test.scss", "@import 'package:nope/test';").create();
+
+    var sass = runSass(["test.scss", "test.css"]);
+    sass.stderr.expect(inOrder([
+      "Error: \"package:\" URLs aren't supported on this platform.",
+      "@import 'package:nope/test';",
+      "        ^^^^^^^^^^^^^^^^^^^",
+      "  test.scss 1:9  root stylesheet"
+    ]));
+    sass.shouldExit(65);
+  });
 }

test/dart_script_test.dart

@@ -0,0 +1,40 @@
+// Copyright 2017 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:package_resolver/package_resolver.dart';
+import 'package:path/path.dart' as p;
+import 'package:scheduled_test/descriptor.dart' as d;
+import 'package:scheduled_test/scheduled_test.dart';
+
+import 'package:sass/sass.dart';
+import 'package:sass/src/exception.dart';
+
+import 'utils.dart';
+
+main() {
+  useSandbox();
+
+  test("successfully imports a package URL", () {
+    d.dir("subdir", [d.file("test.scss", "a {b: 1 + 2}")]).create();
+
+    d.file("test.scss", '@import "package:fake_package/test";').create();
+    var resolver = new SyncPackageResolver.config(
+        {"fake_package": p.toUri(p.join(sandbox, 'subdir'))});
+
+    schedule(() {
+      var css = render(p.join(sandbox, "test.scss"), packageResolver: resolver);
+      expect(css, equals("a {\n  b: 3;\n}"));
+    });
+  });
+
+  test("imports a package URL from a missing package", () {
+    d.file("test.scss", '@import "package:fake_package/test_aux";').create();
+    var resolver = new SyncPackageResolver.config({});
+
+    schedule(() {
+      expect(() => render(sandbox + "/test.scss", packageResolver: resolver),
+          throwsA(new isInstanceOf<SassRuntimeException>()));
+    });
+  });
+}