Generalizes to support multiple migrators

CONTRIBUTING.md

@@ -23,7 +23,7 @@ All submissions, including submissions by project members, require review.
 ### File headers
 All files in the project must start with the following header.
 
-    // Copyright 2018 Google LLC
+    // Copyright 2019 Google LLC
     //
     // Use of this source code is governed by an MIT-style
     // license that can be found in the LICENSE file or at

bin/sass_migrator.dart

@@ -0,0 +1,9 @@
+// Copyright 2019 Google LLC
+//
+// 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:sass_migrator/runner.dart';
+
+main(List<String> args) => MigratorRunner().execute(args);

lib/runner.dart

@@ -0,0 +1,59 @@
+// Copyright 2019 Google LLC
+//
+// 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 'dart:io';
+
+import 'package:args/command_runner.dart';
+import 'package:path/path.dart' as p;
+
+import 'src/migrators/module.dart';
+
+/// A command runner that runs a migrator based on provided arguments.
+class MigratorRunner extends CommandRunner<p.PathMap<String>> {
+  final invocation = "sass_migrator <migrator> [options] <entrypoint.scss...>";
+
+  MigratorRunner()
+      : super("sass_migrator", "Migrates stylesheets to new Sass versions.") {
+    argParser.addFlag('migrate-deps',
+        abbr: 'd', help: 'Migrate dependencies in addition to entrypoints.');
+    argParser.addFlag('dry-run',
+        abbr: 'n',
+        help: 'Show which files would be migrated but make no changes.');
+    argParser.addFlag('verbose',
+        abbr: 'v',
+        help: 'Print text of migrated files when running with --dry-run.');
+    addCommand(ModuleMigrator());
+  }
+
+  /// Runs a migrator and then writes the migrated files to disk unless
+  /// --dry-run is passed.
+  Future execute(Iterable<String> args) async {
+    var argResults = parse(args);
+    var migrated = await runCommand(argResults);
+    if (migrated == null) return;
+
+    if (migrated.isEmpty) {
+      print('Nothing to migrate!');
+      return;
+    }
+
+    if (argResults['dry-run']) {
+      print('Dry run. Logging migrated files instead of overwriting...\n');
+      for (var path in migrated.keys) {
+        print('$path');
+        if (argResults['verbose']) {
+          print('=' * 80);
+          print(migrated[path]);
+        }
+      }
+    } else {
+      for (var path in migrated.keys) {
+        if (argResults['verbose']) print("Overwriting $path...");
+        File(path).writeAsStringSync(migrated[path]);
+      }
+    }
+  }
+}

lib/src/migration_visitor.dart

@@ -0,0 +1,101 @@
+// Copyright 2019 Google LLC
+//
+// 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 'dart:io';
+
+// The sass package's API is not necessarily stable. It is being imported with
+// the Sass team's explicit knowledge and approval. See
+// https://github.com/sass/dart-sass/issues/236.
+import 'package:sass/src/ast/sass.dart';
+import 'package:sass/src/syntax.dart';
+import 'package:sass/src/visitor/recursive_ast.dart';
+
+import 'package:path/path.dart' as p;
+
+import 'migrator.dart';
+import 'patch.dart';
+import 'utils.dart';
+
+/// A visitor that migrates a stylesheet.
+///
+/// When [run] is called, this visitor traverses a stylesheet's AST, allowing
+/// subclasses to override one or more methods and add to [patches]. Once the
+/// stylesheet has been visited, the migrated contents (based on [patches]) will
+/// be stored in [migrator]'s [migrated] map.
+///
+/// If [migrateDependencies] is enabled, this visitor will construct and run a
+/// new instance of itself (using [newInstance]) each time it encounters an
+/// @import or @use rule.
+abstract class MigrationVisitor extends RecursiveAstVisitor {
+  /// The migrator running on this stylesheet.
+  Migrator get migrator;
+
+  /// The canonical path of the stylesheet being migrated.
+  String get path;
+
+  /// The stylesheet being migrated.
+  Stylesheet stylesheet;
+
+  /// The syntax this stylesheet uses.
+  Syntax syntax;
+
+  /// The patches to be applied to the stylesheet being migrated.
+  final List<Patch> patches = [];
+
+  /// Returns a new instance of this MigrationVisitor with the same migrator
+  /// and [newPath].
+  MigrationVisitor newInstance(String newPath);
+
+  /// Runs the migrator and stores the migrated contents in `migrator.migrated`.
+  void run() {
+    var contents = File(path).readAsStringSync();
+    syntax = Syntax.forPath(path);
+    stylesheet = Stylesheet.parse(contents, syntax, url: path);
+    visitStylesheet(stylesheet);
+    var results = getMigratedContents();
+    if (results != null) {
+      migrator.migrated[path] = results;
+    }
+  }
+
+  /// Returns the migrated contents of this file, or null if the file does not
+  /// change.
+  ///
+  /// This will be called by [run] and the results will be stored in
+  /// `migrator.migrated`.
+  String getMigratedContents() => patches.isNotEmpty
+      ? Patch.applyAll(patches.first.selection.file, patches)
+      : null;
+
+  /// Returns the canonical path of [url] when resolved relative to the current
+  /// path.
+  String resolveImportUrl(String url) =>
+      canonicalizePath(p.join(p.dirname(path), url));
+
+  /// If [migrator.migrateDependencies] is enabled, any dynamic imports within
+  /// this [node] will be migrated before continuing.
+  @override
+  visitImportRule(ImportRule node) {
+    super.visitImportRule(node);
+    for (var import in node.imports) {
+      if (import is DynamicImport) {
+        if (migrator.migrateDependencies) {
+          newInstance(resolveImportUrl(import.url)).run();
+        }
+      }
+    }
+  }
+
+  /// If [migrator.migrateDependencies] is enabled, this dependency will be
+  /// migrated before continuing.
+  @override
+  visitUseRule(UseRule node) {
+    super.visitUseRule(node);
+    if (migrator.migrateDependencies) {
+      newInstance(resolveImportUrl(node.url.toString())).run();
+    }
+  }
+}