Don't load transformers that aren't going to be used for an executable.

sdk/lib/_internal/pub/lib/src/barback/transformers_needed_by_transformers.dart

Index: sdk/lib/_internal/pub/lib/src/barback/transformers_needed_by_transformers.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/transformers_needed_by_transformers.dart b/sdk/lib/_internal/pub/lib/src/barback/transformers_needed_by_transformers.dart
deleted file mode 100644
index e32b42b6efc594bdff0dd0a9bc57a771c0372a5b..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub/lib/src/barback/transformers_needed_by_transformers.dart
+++ /dev/null
@@ -1,399 +0,0 @@
-// Copyright (c) 2014, 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.
-
-library pub.barback.transformers_needed_by_transformers;
-
-import 'package:path/path.dart' as p;
-
-import '../dart.dart';
-import '../io.dart';
-import '../package.dart';
-import '../package_graph.dart';
-import '../utils.dart';
-import 'cycle_exception.dart';
-import 'transformer_config.dart';
-import 'transformer_id.dart';
-
-/// Returns a dependency graph for transformers in [graph].
-///
-/// This graph is represented by a map whose keys are the vertices and whose
-/// values are sets representing edges from the given vertex. Each vertex is a
-/// [TransformerId]. If there's an edge from `T1` to `T2`, then `T2` must be
-/// loaded before `T1` can be loaded.
-///
-/// The returned graph is transitively closed. That is, if there's an edge from
-/// `T1` to `T2` and an edge from `T2` to `T3`, there's also an edge from `T1`
-/// to `T2`.
-Map<TransformerId, Set<TransformerId>> computeTransformersNeededByTransformers(
-    PackageGraph graph) {
-  var result = {};
-  var computer = new _DependencyComputer(graph);
-  for (var packageName in ordered(graph.packages.keys)) {
-    var package = graph.packages[packageName];
-    for (var phase in package.pubspec.transformers) {
-      for (var config in phase) {
-        var id = config.id;
-        if (id.isBuiltInTransformer) continue;
-        if (id.package != graph.entrypoint.root.name &&
-            !config.canTransformPublicFiles) {
-          continue;
-        }
-        result[id] = computer.transformersNeededByTransformer(id);
-      }
-    }
-  }
-  return result;
-}
-
-/// A helper class for [computeTransformersNeededByTransformers] that keeps
-/// package-graph-wide state and caches over the course of the computation.
-class _DependencyComputer {
-  /// The package graph being analyzed.
-  final PackageGraph _graph;
-
-  /// The names of packages for which [_PackageDependencyComputer]s are
-  /// currently loading.
-  ///
-  /// This is used to detect transformer cycles. If a package's libraries or
-  /// transformers are referenced while the transformers that apply to it are
-  /// being processed, that indicates an unresolvable cycle.
-  final _loadingPackageComputers = new Set<String>();
-
-  /// [_PackageDependencyComputer]s that have been loaded.
-  final _packageComputers = new Map<String, _PackageDependencyComputer>();
-
-  /// A cache of the results of [transformersNeededByPackage].
-  final _transformersNeededByPackages = new Map<String, Set<TransformerId>>();
-
-  _DependencyComputer(this._graph) {
-    ordered(_graph.packages.keys).forEach(_loadPackageComputer);
-  }
-
-  /// Returns the set of all transformers that need to be loaded before [id] is
-  /// loaded.
-  Set<TransformerId> transformersNeededByTransformer(TransformerId id) {
-    if (id.isBuiltInTransformer) return new Set();
-    _loadPackageComputer(id.package);
-    return _packageComputers[id.package].transformersNeededByTransformer(id);
-  }
-
-  /// Returns the set of all transformers that need to be loaded before
-  /// [packageUri] (a "package:" URI) can be safely imported from an external
-  /// package.
-  Set<TransformerId> transformersNeededByPackageUri(Uri packageUri) {
-    // TODO(nweiz): We can do some pre-processing on the package graph (akin to
-    // the old ordering dependency computation) to figure out which packages are
-    // guaranteed not to require any transformers. That'll let us avoid extra
-    // work here and in [transformersNeededByPackage].
-
-    var components = p.split(p.fromUri(packageUri.path));
-    var packageName = components.first;
-    var package = _graph.packages[packageName];
-    if (package == null) {
-      // TODO(nweiz): include source range information here.
-      fail('A transformer imported unknown package "$packageName" (in '
-          '"$packageUri").');
-    }
-
-    var library = package.path('lib', p.joinAll(components.skip(1)));
-
-    _loadPackageComputer(packageName);
-    return _packageComputers[packageName].transformersNeededByLibrary(library);
-  }
-
-  /// Returns the set of all transformers that need to be loaded before
-  /// everything in [rootPackage] can be used.
-  ///
-  /// This is conservative in that it returns all transformers that could
-  /// theoretically affect [rootPackage]. It only looks at which transformers
-  /// packages use and which packages they depend on; it ignores imports
-  /// entirely.
-  ///
-  /// We fall back on this conservative analysis when a transformer
-  /// (transitively) imports a transformed library. The result of the
-  /// transformation may import any dependency or hit any transformer, so we
-  /// have to assume that it will.
-  Set<TransformerId> transformersNeededByPackage(String rootPackage) {
-    if (_transformersNeededByPackages.containsKey(rootPackage)) {
-      return _transformersNeededByPackages[rootPackage];
-    }
-
-    var results = new Set();
-    var seen = new Set();
-
-    traversePackage(packageName) {
-      if (seen.contains(packageName)) return;
-      seen.add(packageName);
-
-      var package = _graph.packages[packageName];
-      for (var phase in package.pubspec.transformers) {
-        for (var config in phase) {
-          var id = config.id;
-          if (id.isBuiltInTransformer) continue;
-          if (_loadingPackageComputers.contains(id.package)) {
-            throw new CycleException("$packageName is transformed by $id");
-          }
-          results.add(id);
-        }
-      }
-
-      var dependencies = packageName == _graph.entrypoint.root.name ?
-          package.immediateDependencies : package.dependencies;
-      for (var dep in dependencies) {
-        try {
-          traversePackage(dep.name);
-        } on CycleException catch (error) {
-          throw error.prependStep("$packageName depends on ${dep.name}");
-        }
-      }
-    }
-
-    traversePackage(rootPackage);
-    _transformersNeededByPackages[rootPackage] = results;
-    return results;
-  }
-
-
-  /// Ensure that a [_PackageDependencyComputer] for [packageName] is loaded.
-  ///
-  /// If the computer has already been loaded, this does nothing. If the
-  /// computer is in the process of being loaded, this throws a
-  /// [CycleException].
-  void _loadPackageComputer(String packageName) {
-    if (_loadingPackageComputers.contains(packageName)) {
-      throw new CycleException();
-    }
-    if (_packageComputers.containsKey(packageName)) return;
-    _loadingPackageComputers.add(packageName);
-    _packageComputers[packageName] =
-        new _PackageDependencyComputer(this, packageName);
-    _loadingPackageComputers.remove(packageName);
-  }
-}
-
-/// A helper class for [computeTransformersNeededByTransformers] that keeps
-/// package-specific state and caches over the course of the computation.
-class _PackageDependencyComputer {
-  /// The parent [_DependencyComputer].
-  final _DependencyComputer _dependencyComputer;
-
-  /// The package whose dependencies [this] is computing.
-  final Package _package;
-
-  /// The set of transformers that currently apply to [this].
-  ///
-  /// This is added to phase-by-phase while [this] is being initialized. This is
-  /// necessary to model the dependencies of a transformer that's applied to its
-  /// own package.
-  final _applicableTransformers = new Set<TransformerConfig>();
-
-  /// A cache of imports and exports parsed from libraries in this package.
-  final _directives = new Map<Uri, Set<Uri>>();
-
-  /// The set of libraries for which there are currently active
-  /// [transformersNeededByLibrary] calls.
-  ///
-  /// This is used to guard against infinite loops caused by libraries in
-  /// different packages importing one another circularly.
-  /// [transformersNeededByLibrary] will return an empty set for any active
-  /// libraries.
-  final _activeLibraries = new Set<String>();
-
-  /// A cache of the results of [transformersNeededByTransformer].
-  final _transformersNeededByTransformers =
-      new Map<TransformerId, Set<TransformerId>>();
-
-  /// A cache of the results of [_getTransitiveExternalDirectives].
-  ///
-  /// This is invalidated whenever [_applicableTransformers] changes.
-  final _transitiveExternalDirectives = new Map<String, Set<Uri>>();
-
-  _PackageDependencyComputer(_DependencyComputer dependencyComputer,
-          String packageName)
-      : _dependencyComputer = dependencyComputer,
-        _package = dependencyComputer._graph.packages[packageName] {
-    // If [_package] uses its own transformers, there will be fewer transformers
-    // running on [_package] while its own transformers are loading than there
-    // will be once all its transformers are finished loading. To handle this,
-    // we run [transformersNeededByTransformer] to pre-populate
-    // [_transformersNeededByLibraries] while [_applicableTransformers] is
-    // smaller.
-    for (var phase in _package.pubspec.transformers) {
-      for (var config in phase) {
-        var id = config.id;
-        try {
-          if (id.package != _package.name) {
-            // Probe [id]'s transformer dependencies to ensure that it doesn't
-            // depend on this package. If it does, a CycleError will be thrown.
-            _dependencyComputer.transformersNeededByTransformer(id);
-          } else {
-            // Store the transformers needed specifically with the current set
-            // of [_applicableTransformers]. When reporting this transformer's
-            // dependencies, [computeTransformersNeededByTransformers] will use
-            // this stored set of dependencies rather than the potentially wider
-            // set that would be recomputed if [transformersNeededByLibrary]
-            // were called anew.
-            _transformersNeededByTransformers[id] =
-                transformersNeededByLibrary(_package.transformerPath(id));
-          }
-        } on CycleException catch (error) {
-          throw error.prependStep("$packageName is transformed by $id");
-        }
-      }
-
-      // Clear the cached imports and exports because the new transformers may
-      // start transforming a library whose directives were previously
-      // statically analyzable.
-      _transitiveExternalDirectives.clear();
-      _applicableTransformers.addAll(phase);
-    }
-  }
-
-  /// Returns the set of all transformers that need to be loaded before [id] is
-  /// loaded.
-  ///
-  /// [id] must refer to a transformer in [_package].
-  Set<TransformerId> transformersNeededByTransformer(TransformerId id) {
-    assert(id.package == _package.name);
-    if (_transformersNeededByTransformers.containsKey(id)) {
-      return _transformersNeededByTransformers[id];
-    }
-
-    _transformersNeededByTransformers[id] =
-        transformersNeededByLibrary(_package.transformerPath(id));
-    return _transformersNeededByTransformers[id];
-  }
-
-  /// Returns the set of all transformers that need to be loaded before
-  /// [library] is imported.
-  ///
-  /// If [library] or anything it imports/exports within this package is
-  /// transformed by [_applicableTransformers], this will return a conservative
-  /// set of transformers (see also
-  /// [_DependencyComputer.transformersNeededByPackage]).
-  Set<TransformerId> transformersNeededByLibrary(String library) {
-    library = p.normalize(library);
-    if (_activeLibraries.contains(library)) return new Set();
-    _activeLibraries.add(library);
-
-    try {
-      var externalDirectives = _getTransitiveExternalDirectives(library);
-      if (externalDirectives == null) {
-        var rootName = _dependencyComputer._graph.entrypoint.root.name;
-        var dependencies = _package.name == rootName ?
-            _package.immediateDependencies : _package.dependencies;
-
-        // If anything transitively imported/exported by [library] within this
-        // package is modified by a transformer, we don't know what it will
-        // load, so we take the conservative approach and say it depends on
-        // everything.
-        return _applicableTransformers.map((config) => config.id).toSet().union(
-            unionAll(dependencies.map((dep) {
-          try {
-            return _dependencyComputer.transformersNeededByPackage(dep.name);
-          } on CycleException catch (error) {
-            throw error.prependStep("${_package.name} depends on ${dep.name}");
-          }
-        })));
-      } else {
-        // If nothing's transformed, then we only depend on the transformers
-        // used by the external packages' libraries that we import or export.
-        return unionAll(externalDirectives.map((uri) {
-          try {
-            return _dependencyComputer.transformersNeededByPackageUri(uri);
-          } on CycleException catch (error) {
-            var packageName = p.url.split(uri.path).first;
-            throw error.prependStep("${_package.name} depends on $packageName");
-          }
-        }));
-      }
-    } finally {
-      _activeLibraries.remove(library);
-    }
-  }
-
-  /// Returns the set of all external package libraries transitively imported or
-  /// exported by [rootLibrary].
-  ///
-  /// All of the returned URIs will have the "package:" scheme. None of them
-  /// will be URIs for this package.
-  ///
-  /// If [rootLibrary] transitively imports or exports a library that's modified
-  /// by a transformer, this will return `null`.
-  Set<Uri> _getTransitiveExternalDirectives(String rootLibrary) {
-    rootLibrary = p.normalize(rootLibrary);
-    if (_transitiveExternalDirectives.containsKey(rootLibrary)) {
-      return _transitiveExternalDirectives[rootLibrary];
-    }
-
-    var results = new Set();
-    var seen = new Set();
-
-    traverseLibrary(library) {
-      library = p.normalize(library);
-      if (seen.contains(library)) return true;
-      seen.add(library);
-
-      var directives = _getDirectives(library);
-      if (directives == null) return false;
-
-      for (var uri in directives) {
-        var path;
-        if (uri.scheme == 'package') {
-          var components = p.split(p.fromUri(uri.path));
-          if (components.first != _package.name) {
-            results.add(uri);
-            continue;
-          }
-
-          path = _package.path('lib', p.joinAll(components.skip(1)));
-        } else if (uri.scheme == '' || uri.scheme == 'file') {
-          path = p.join(p.dirname(library), p.fromUri(uri));
-        } else {
-          // Ignore "dart:" URIs and theoretically-possible "http:" URIs.
-          continue;
-        }
-
-        if (!traverseLibrary(path)) return false;
-      }
-
-      return true;
-    }
-
-    _transitiveExternalDirectives[rootLibrary] =
-        traverseLibrary(rootLibrary) ? results : null;
-    return _transitiveExternalDirectives[rootLibrary];
-  }
-
-  /// Returns the set of all imports or exports in [library].
-  ///
-  /// If [library] is modified by a transformer, this will return `null`.
-  Set<Uri> _getDirectives(String library) {
-    var libraryUri = p.toUri(p.normalize(library));
-    var relative = p.toUri(_package.relative(library)).path;
-    if (_applicableTransformers.any((config) =>
-            config.canTransform(relative))) {
-      _directives[libraryUri] = null;
-      return null;
-    }
-
-    // Check the cache *after* checking [_applicableTransformers] because
-    // [_applicableTransformers] changes over time so the directives may be
-    // invalidated.
-    if (_directives.containsKey(libraryUri)) return _directives[libraryUri];
-
-    // If a nonexistent library is imported, it will probably be generated by a
-    // transformer.
-    if (!fileExists(library)) {
-      _directives[libraryUri] = null;
-      return null;
-    }
-
-    _directives[libraryUri] =
-        parseImportsAndExports(readTextFile(library), name: library)
-        .map((directive) => Uri.parse(directive.uri.stringValue))
-        .toSet();
-    return _directives[libraryUri];
-  }
-}