Implement modular compilation

lib/src/codegen/module_builder.dart

-// Copyright (c) 2015, 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 'package:path/path.dart' as path;
-
-import '../js/js_ast.dart' as JS;
-import '../js/js_ast.dart' show js;
-import '../options.dart' show ModuleFormat;
-
-/// Helper that builds JS modules in a given [ModuleFormat].
-abstract class ModuleBuilder {
-  final _exports = <String, String>{};
-  final _imports = <_ModuleImport>[];
-
-  ModuleBuilder._();
-
-  /// Returns a [format]-specific [ModuleBuilder].
-  /// - [jsPath] is the path of the module being built.
-  /// - [jsModuleValue] is the default value to use for the library, in case of
-  ///   js interop (comes from the @js.JS(jsModuleValue) annotation on the
-  ///   library directive). It is null in any other case.
-  /// - [exportsVar] is the name of the object on which items are exported. Lazy
-  ///   variables and constants are assumed to be declared on this instance.
-  factory ModuleBuilder(ModuleFormat format) {
-    switch (format) {
-      case ModuleFormat.legacy:
-        return new LegacyModuleBuilder();
-      case ModuleFormat.es6:
-        return new ES6ModuleBuilder();
-      case ModuleFormat.node:
-        return new NodeModuleBuilder();
-    }
-  }
-
-  /// Adds [name] to the list of names to be exported from the module.
-  void addExport(String name, String exportName) {
-    _exports[name] = exportName;
-  }
-
-  /// Adds an import from a module named [name] and locally aliased as [libVar].
-  /// When [isLazy] is `true`, the import should be lazy (i.e. there is some
-  /// cyclic dependency of imports).
-  /// When [libVar] is `null`, the import is there just to force the import
-  /// order.
-  void addImport(String name, JS.Identifier libVar, {bool isLazy: false}) {
-    _imports.add(new _ModuleImport(name, libVar, isLazy));
-  }
-
-  /// Builds a program out of menu items.
-  JS.Program build(String jsPath, String jsModuleValue,
-      JS.Identifier exportsVar, Iterable<JS.ModuleItem> moduleItems);
-}
-
-class _ModuleImport {
-  final String name;
-  final JS.Identifier libVar;
-  // TODO(jmesserly): Assess whether we can remove this (we shouldn't need it
-  // even in our legacy module format, but it might still be useful for Closure
-  // with ES6 modules).
-  final bool isLazy;
-  _ModuleImport(this.name, this.libVar, this.isLazy);
-}
-
-/// Generates modules for with DDC's `dart_library.js` loading mechanism.
-class LegacyModuleBuilder extends ModuleBuilder {
-  LegacyModuleBuilder() : super._();
-
-  JS.Program build(String jsPath, String jsModuleValue,
-      JS.Identifier exportsVar, Iterable<JS.ModuleItem> moduleItems) {
-    // TODO(jmesserly): it would be great to run the renamer on the body,
-    // then figure out if we really need each of these parameters.
-    // See ES6 modules: https://github.com/dart-lang/dev_compiler/issues/34
-    var params = [exportsVar];
-    var lazyParams = [];
-
-    var imports = <JS.Expression>[];
-    var lazyImports = <JS.Expression>[];
-    var moduleStatements = <JS.Statement>[];
-
-    for (var i in _imports) {
-      // No need to force the import order for the legacy library mechanism.
-      if (i.libVar == null) continue;
-      (i.isLazy ? lazyImports : imports).add(js.string(i.name, "'"));
-      (i.isLazy ? lazyParams : params).add(i.libVar);
-    }
-    params.addAll(lazyParams);
-
-    moduleStatements.addAll(_flattenBlocks(moduleItems));
-
-    if (_exports.isNotEmpty) {
-      moduleStatements.add(js.comment('Exports:'));
-      // TODO(jmesserly): make these immutable in JS?
-      _exports.forEach((name, exportName) {
-        moduleStatements
-            .add(js.statement('#.# = #;', [exportsVar, exportName, name]));
-      });
-    }
-
-    var module =
-        js.call("function(#) { 'use strict'; #; }", [params, moduleStatements]);
-
-    var moduleDef = js.statement("dart_library.library(#, #, #, #, #)", [
-      js.string(jsPath, "'"),
-      jsModuleValue ?? new JS.LiteralNull(),
-      js.commentExpression(
-          "Imports", new JS.ArrayInitializer(imports, multiline: true)),
-      js.commentExpression("Lazy imports",
-          new JS.ArrayInitializer(lazyImports, multiline: true)),
-      module
-    ]);
-    return new JS.Program(<JS.ModuleItem>[moduleDef]);
-  }
-}
-
-String _relativeModuleName(String moduleName, {String from}) {
-  var relativeName =
-      path.relative('/' + moduleName, from: path.dirname('/$from'));
-  return relativeName.startsWith('.') ? relativeName : './$relativeName';
-}
-
-/// Generates ES6 modules.
-// TODO(ochafik): Break strong dep cycles to accommodate the Closure Compiler.
-class ES6ModuleBuilder extends ModuleBuilder {
-  ES6ModuleBuilder() : super._();
-
-  JS.Program build(String jsPath, String jsModuleValue,
-      JS.Identifier exportsVar, Iterable<JS.ModuleItem> moduleItems) {
-    var moduleStatements = <JS.ModuleItem>[
-      js.statement("const # = {};", [exportsVar])
-    ];
-
-    // TODO(jmesserly): it would be great to run the renamer on the body,
-    // then figure out if we really need each of these parameters.
-    // See ES6 modules: https://github.com/dart-lang/dev_compiler/issues/34
-    for (var i in _imports) {
-      var moduleName = js.string(_relativeModuleName(i.name, from: jsPath));
-      // TODO(ochafik): laziness, late binding, etc, to support Closure...
-      if (i.libVar == null) {
-        moduleStatements
-            .add(new JS.ImportDeclaration(namedImports: [], from: moduleName));
-      } else {
-        moduleStatements.add(new JS.ImportDeclaration(
-            defaultBinding: i.libVar, from: moduleName));
-      }
-    }
-
-    moduleStatements.addAll(_flattenBlocks(moduleItems));
-
-    if (_exports.isNotEmpty) {
-      moduleStatements.add(js.comment('Exports:'));
-      // TODO(jmesserly): make these immutable in JS?
-      _exports.forEach((name, exportName) {
-        moduleStatements
-            .add(js.statement('#.# = #;', [exportsVar, exportName, name]));
-      });
-    }
-    moduleStatements.add(new JS.ExportDeclaration(exportsVar, isDefault: true));
-    // TODO(ochafik): What to do with jsModuleValue?
-    return new JS.Program(moduleStatements);
-  }
-}
-
-/// Generates node modules.
-class NodeModuleBuilder extends ModuleBuilder {
-  NodeModuleBuilder() : super._();
-
-  JS.Program build(String jsPath, String jsModuleValue,
-      JS.Identifier exportsVar, Iterable<JS.ModuleItem> moduleItems) {
-    var moduleStatements = <JS.ModuleItem>[js.statement("'use strict';"),];
-
-    for (var i in _imports) {
-      if (i.libVar == null) {
-        moduleStatements.add(js.statement('require(#);', [js.string(i.name)]));
-      } else {
-        moduleStatements.add(
-            js.statement('let # = require(#);', [i.libVar, js.string(i.name)]));
-      }
-    }
-
-    moduleStatements.addAll(_flattenBlocks(moduleItems));
-
-    if (_exports.isNotEmpty) {
-      moduleStatements.add(js.comment('Exports:'));
-      _exports.forEach((name, exportName) {
-        moduleStatements
-            .add(js.statement('#.# = #;', [exportsVar, exportName, name]));
-      });
-    }
-    // TODO(ochafik): What to do with jsModuleValue?
-    // (something like `let exports = jsModuleValue;`?)
-    return new JS.Program(moduleStatements);
-  }
-}
-
-/// Flattens blocks in [stats] to a single list of module items.
-/// Note that in general, blocks should not be flattened, because it can
-/// mess up with block-level scoping (let, const).
-// TODO(ochafik): Remove this / find better pattern (adding statements as they
-// are generated from [JSCodegenVisitor], instead of composing them with
-// [_statements]).
-Iterable<JS.ModuleItem> _flattenBlocks(List<JS.ModuleItem> stats) =>
-    stats.expand(
-        (item) => item is JS.Block ? _flattenBlocks(item.statements) : [item]);