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

pkg/polymer/lib/src/build/script_compactor.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 combines multiple dart script tags into a single one.
 library polymer.src.build.script_compactor;
 
 import 'dart:async';
 import 'dart:convert';
 
@@ skipping 121 matching lines @@
         logger.warning('unexpected script. The '
           'ScriptCompactor transformer should run after running the '
           'ImportInliner', span: tag.sourceSpan);
       }
     }
   }
 
   /// Emits the main HTML and Dart bootstrap code for the application. If there
   /// were not Dart entry point files, then this simply emits the original HTML.
   Future _emitNewEntrypoint(_) {
-    if (entryLibraries.isEmpty) {
-      // We didn't find code, nothing to do.
-      transform.addOutput(transform.primaryInput);
-      return null;
-    }
-
+    // If we don't find code, there is nothing to do.
+    if (entryLibraries.isEmpty) return null;
     return _initResolver()
         .then(_extractUsesOfMirrors)
         .then(_emitFiles)
         .whenComplete(() {
           if (resolver != null) resolver.release();
         });
   }
 
   /// Load a resolver that computes information for every library in
   /// [entryLibraries], then use it to initialize the [recorder] (for import
   /// resolution) and to resolve specific elements (for analyzing the user's
   /// code).
-  Future _initResolver() => resolvers.get(transform, entryLibraries).then((r) {
-    resolver = r;
-    types = new _ResolvedTypes(resolver);
-  });
+  Future _initResolver() {
+    // We include 'polymer.dart' to simplify how we do resolution below. This
+    // way we can assume polymer is there, even if the user didn't include an
+    // import to it. If not, the polymer build will fail with an error when
+    // trying to create _ResolvedTypes below.
+    var libsToLoad = [new AssetId('polymer', 'lib/polymer.dart')]
+        ..addAll(entryLibraries);
+    return resolvers.get(transform, libsToLoad).then((r) {
+      resolver = r;
+      types = new _ResolvedTypes(resolver);
+    });
+  }
 
   /// Inspects the entire program to find out anything that polymer accesses
   /// using mirrors and produces static information that can be used to replace
   /// the mirror-based loader and the uses of mirrors through the `smoke`
   /// package. This includes:
   ///
   ///   * visiting entry-libraries to extract initializers,
   ///   * visiting polymer-expressions to extract getters and setters,
   ///   * looking for published fields of custom elements, and
   ///   * looking for event handlers and callbacks of change notifications.
@@ skipping 164 matching lines @@
       code.writeln("import '$url' as i$i;");
       prefixes[id] = 'i$i';
       i++;
     }
 
     // Include smoke initialization.
     generator.writeImports(code);
     generator.writeTopLevelDeclarations(code);
     code.writeln('\nvoid main() {');
     generator.writeInitCall(code);
-    code.writeln('  startPolymer([');
+    code.write('  startPolymer([');
 
     // Include initializers to switch from mirrors_loader to static_loader.
-    for (var init in initializers) {
-      var initCode = init.asCode(prefixes[init.assetId]);
-      code.write("      $initCode,\n");
+    if (!initializers.isEmpty) {
+      code.writeln();
+      for (var init in initializers) {
+        var initCode = init.asCode(prefixes[init.assetId]);
+        code.write("      $initCode,\n");
+      }
+      code.writeln('    ]);');
+    } else {
+      logger.warning(NO_INITIALIZERS_ERROR);
+      code.writeln(']);');
     }
-    code..writeln('    ]);')
-        ..writeln('}');
+    code.writeln('}');
     transform.addOutput(new Asset.fromString(bootstrapId, code.toString()));
 
 
     // Emit the bootstrap .dart file
     var srcUrl = path.url.basename(bootstrapId.path);
     document.body.nodes.add(parseFragment(
           '<script type="application/dart" src="$srcUrl"></script>'));
     transform.addOutput(new Asset.fromString(docId, document.outerHtml));
   }
 
@@ skipping 30 matching lines @@
 }
 
 _getSpan(SourceFile file, AstNode node) => file.span(node.offset, node.end);
 
 const MAIN_HEADER = """
 library app_bootstrap;
 
 import 'package:polymer/polymer.dart';
 """;
 
+const NO_INITIALIZERS_ERROR =
+    'No polymer initializers were found. Make sure to either '
+    'annotate your polymer elements with @CustomTag or include a '
+    'top level method annotated with @initMethod that registers your '
+    'elements. Both annotations are defined in the polymer library ('
+    'package:polymer/polymer.dart).';
+
 /// An html visitor that:
 ///   * finds all polymer expressions and records the getters and setters that
 ///     will be needed to evaluate them at runtime.
 ///   * extracts all attributes declared in the `attribute` attributes of
 ///     polymer elements.
 class _HtmlExtractor extends TreeVisitor {
   final Map<String, List<String>> publishedAttributes;
   final SmokeCodeGenerator generator;
   final _SubExpressionVisitor visitor;
   bool _inTemplate = false;
@@ skipping 272 matching lines @@
   for (var c in combinators) {
     if (c is ShowElementCombinator) {
       var show = c.shownNames.toSet();
       elements.retainWhere((e) => show.contains(e.displayName));
     } else if (c is HideElementCombinator) {
       var hide = c.hiddenNames.toSet();
       elements.removeWhere((e) => hide.contains(e.displayName));
     }
   }
 }