Detect and warn about missing scripts (rather than fail during the build)

pkg/polymer/lib/src/build/import_inliner.dart

 // Copyright (c) 2013, 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.
 
 /// Transfomer that inlines polymer-element definitions from html imports.
 library polymer.src.build.import_inliner;
 
 import 'dart:async';
 import 'dart:convert';
 
@@ skipping 10 matching lines @@
 import 'common.dart';
 
 // TODO(sigmund): move to web_components package (dartbug.com/18037).
 class _HtmlInliner extends PolymerTransformer {
   final TransformOptions options;
   final Transform transform;
   final TransformLogger logger;
   final AssetId docId;
   final seen = new Set<AssetId>();
   final scriptIds = <AssetId>[];
+  final extractedFiles = new Set<AssetId>();
 
   /// The number of extracted inline Dart scripts. Used as a counter to give
   /// unique-ish filenames.
   int inlineScriptCounter = 0;
 
   _HtmlInliner(this.options, Transform transform)
       : transform = transform,
         logger = transform.logger,
         docId = transform.primaryInput.id;
 
   Future apply() {
     seen.add(docId);
 
     Document document;
     bool changed;
 
     return readPrimaryAsHtml(transform).then((doc) {
       document = doc;
       // Add the main script's ID, or null if none is present.
       // This will be used by ScriptCompactor.
       changed = _extractScripts(document, docId);
       return _visitImports(document);
     }).then((importsFound) {
-      bool scriptsRemoved = _removeScripts(document);
-      changed = changed || importsFound || scriptsRemoved;
+      changed = changed || importsFound;
+      return _removeScripts(document);
+    }).then((scriptsRemoved) {
+      changed = changed || scriptsRemoved;
 
       var output = transform.primaryInput;
       if (changed) output = new Asset.fromString(docId, document.outerHtml);
       transform.addOutput(output);
 
       // We produce a secondary asset with extra information for later phases.
       transform.addOutput(new Asset.fromString(
           docId.addExtension('.scriptUrls'),
           JSON.encode(scriptIds, toEncodable: (id) => id.serialize())));
     });
@@ skipping 87 matching lines @@
       css = new _UrlNormalizer(transform, id).visitCss(css);
       link.replaceWith(new Element.tag('style')..text = css);
     });
   }
 
   /// Remove "application/dart;component=1" scripts and remember their
   /// [AssetId]s for later use.
   ///
   /// Dartium only allows a single script tag per page, so we can't inline
   /// the script tags. Instead we remove them entirely.
-  bool _removeScripts(Document doc) {
+  Future<bool> _removeScripts(Document doc) {
     bool changed = false;
-    for (var script in doc.querySelectorAll('script')) {
+    return Future.forEach(doc.querySelectorAll('script'), (script) {
       if (script.attributes['type'] == TYPE_DART_COMPONENT) {
         changed = true;
         script.remove();
         var src = script.attributes['src'];
-        scriptIds.add(uriToAssetId(docId, src, logger, script.sourceSpan));
+        var srcId = uriToAssetId(docId, src, logger, script.sourceSpan);
+
+        // We check for extractedFiles because 'hasInput' below is only true for
+        // assets that existed before this transformer runs (hasInput is false
+        // for files created by [_extractScripts]).
+        if (extractedFiles.contains(srcId)) {
+          scriptIds.add(srcId);
+          return true;
+        }
+        return transform.hasInput(srcId).then((exists) {
+          if (!exists) {
+            logger.warning('Script file at "$src" not found.',
+              span: script.sourceSpan);
+          } else {
+            scriptIds.add(srcId);
+          }
+        });
       }
-    }
-    return changed;
+    }).then((_) => changed);
   }
 
   /// Split inline scripts into their own files. We need to do this for dart2js
   /// to be able to compile them.
   ///
   /// This also validates that there weren't any duplicate scripts.
   bool _extractScripts(Document doc, AssetId sourceId) {
     bool changed = false;
     bool first = true;
     for (var script in doc.querySelectorAll('script')) {
@@ skipping 28 matching lines @@
         //   myPkgName|web/foo/bar.html -> myPkgName.web.foo.bar_html
         // This should roughly match the recommended library name conventions.
         var libName = '${path.withoutExtension(sourceId.path)}_'
             '${path.extension(sourceId.path).substring(1)}';
         if (libName.startsWith('lib/')) libName = libName.substring(4);
         libName = libName.replaceAll('/', '.').replaceAll('-', '_');
         libName = '${sourceId.package}.${libName}_$count';
 
         code = "library $libName;\n$code";
       }
+      extractedFiles.add(newId);
       transform.addOutput(new Asset.fromString(newId, code));
     }
     return changed;
   }
 }
 
 /// Parse [code] and determine whether it has a library directive.
 bool _hasLibraryDirective(String code) =>
     parseCompilationUnit(code).directives.any((d) => d is LibraryDirective);
 
@@ skipping 159 matching lines @@
 ];
 
 _getSpan(SourceFile file, AstNode node) => file.span(node.offset, node.end);
 
 const COMPONENT_WARNING =
     'More than one Dart script per HTML document is not supported, but in the '
     'near future Dartium will execute each tag as a separate isolate. If this '
     'code is meant to load definitions that are part of the same application '
     'you should switch it to use the "application/dart;component=1" mime-type '
     'instead.';