Dart analyzer fixes to improve pluggability.

compiler/java/com/google/dart/compiler/UrlLibrarySource.java

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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.
 package com.google.dart.compiler;
 
 import java.io.File;
 import java.net.URI;
 
 /**
  * A {@link LibrarySource} backed by a URL.
  */
 public class UrlLibrarySource extends UrlSource implements LibrarySource {
+  
   public UrlLibrarySource(URI uri, PackageLibraryManager slm) {
     super(uri, slm);
   }
 
   public UrlLibrarySource(URI uri) {
     this(uri, null);
   }
 
   public UrlLibrarySource(File file) {
     super(file);
   }
 
   @Override
   public String getName() {
     return getUri().toString();
   }
 
   @Override
-  public DartSource getSourceFor(final String relPath) {
-    if (relPath == null || relPath.isEmpty()) {
-      return null;
-    }
-    try {
-      // Force the creation of an escaped relative URI to deal with spaces, etc.s
-      URI uri = getUri().resolve(new URI(null, null, relPath, null, null)).normalize();
-      return new UrlDartSource(uri, relPath, this, packageLibraryManager);
-    } catch (Throwable e) {
-      return null;
-    }
-  }
-
-  @Override
   public LibrarySource getImportFor(String relPath) {
     if (relPath == null || relPath.isEmpty()) {
       return null;
     }
     try {
       // Force the creation of an escaped relative URI to deal with spaces, etc.
       URI uri = getUri().resolve(new URI(null, null, relPath, null, null)).normalize();
       String path = uri.getPath();
       // Resolve relative reference out of one system library into another
       if (PackageLibraryManager.isDartUri(uri)) {
-        if(path != null && path.startsWith("/..")) {
+        if (path != null && path.startsWith("/..")) {
           URI fileUri = packageLibraryManager.resolveDartUri(uri);
           URI shortUri = packageLibraryManager.getShortUri(fileUri);
           if (shortUri != null) {
             uri = shortUri;
           }
         }
-      } else if (PackageLibraryManager.isPackageUri(uri)){
+      } else if (PackageLibraryManager.isPackageUri(uri)) {
         URI fileUri = packageLibraryManager.resolveDartUri(uri);
-        if (fileUri != null){
+        if (fileUri != null) {
           uri = fileUri;
         }
-      } else if (path != null && !(new File(path).exists())){
+      } else if (!resourceExists(uri)) {
         // resolve against package root directories to find file
-         uri = packageLibraryManager.findExistingFileInPackages(uri);
+        uri = packageLibraryManager.findExistingFileInPackages(uri);
       }
-     
-      return new UrlLibrarySource(uri, packageLibraryManager);
+
+      return createLibrarySource(uri, packageLibraryManager);
     } catch (Throwable e) {
       return null;
     }
   }
+
+  @Override
+  public DartSource getSourceFor(final String relPath) {
+    if (relPath == null || relPath.isEmpty()) {
+      return null;
+    }
+    try {
+      // Force the creation of an escaped relative URI to deal with spaces, etc.
+      URI uri = getUri().resolve(new URI(null, null, relPath, null, null)).normalize();
+      return createDartSource(uri, relPath, this, packageLibraryManager);
+    } catch (Throwable e) {
+      return null;
+    }
+  }
+
+  /**
+   * Create a URL library source. 
+   * 
+   * (Clients can override.)
+   * 
+   * @param uri the URI of the library
+   * @param relPath relative path to the dart source
+   * @param libSource the library source
+   * @param packageManager the package library manager
+   * @return the resulting dart source
+   */
+  protected UrlDartSource createDartSource(URI uri, String relPath, UrlLibrarySource libSource, PackageLibraryManager packageManager) {
+    return new UrlDartSource(uri, relPath, libSource, packageManager);
+  }
+
+  /**
+   * Create a URL library source. 
+   * 
+   * (Clients can override.)
+   * 
+   * @param uri the URI of the library
+   * @return the resulting library source
+   */
+  protected UrlLibrarySource createLibrarySource(URI uri, PackageLibraryManager packageManager) {
+    return new UrlLibrarySource(uri, packageManager);
+  }
+  
+  /**
+   * Check if a resource exists at this URI.
+   * 
+   * (Clients can override.)
+   * 
+   * @param uri the URI to test
+   * @return <code>true</code> if a resource exists at this URI, <code>false</code> otherwise
+   */
+  protected boolean resourceExists(URI uri) {
+    String path = uri.getPath();
+    return path == null || new File(path).exists();
+  }
+  
 }