JS tree shaking for incremental builds.

compiler/java/com/google/dart/compiler/backend/js/JavascriptBackend.java

Index: compiler/java/com/google/dart/compiler/backend/js/JavascriptBackend.java
diff --git a/compiler/java/com/google/dart/compiler/backend/js/JavascriptBackend.java b/compiler/java/com/google/dart/compiler/backend/js/JavascriptBackend.java
index 18c9c8898ff593ae4fd9235ffa326afb0313f8b8..4e6f4f79f23bcba3acc8a8c9b5d5bfbebcfbde3e 100644
--- a/compiler/java/com/google/dart/compiler/backend/js/JavascriptBackend.java
+++ b/compiler/java/com/google/dart/compiler/backend/js/JavascriptBackend.java
@@ -12,6 +12,7 @@ import com.google.dart.compiler.DartSource;
 import com.google.dart.compiler.LibrarySource;
 import com.google.dart.compiler.ast.LibraryNode;
 import com.google.dart.compiler.ast.LibraryUnit;
+import com.google.dart.compiler.backend.js.analysis.TreeShaker;
 import com.google.dart.compiler.common.GenerateSourceMap;
 import com.google.dart.compiler.metrics.CompilerMetrics;
 import com.google.dart.compiler.resolver.CoreTypeProvider;
@@ -83,8 +84,6 @@ public class JavascriptBackend extends AbstractJsBackend  {
 
   private static class DepsWritingCallback implements DepsCallback {
     private final DartCompilerContext context;
-    private long charsWritten = 0;
-    private long nativeCharsWritten = 0;
     private CountingAppendable out;
     private final List<SourceMapSection> appSections;
 
@@ -97,28 +96,12 @@ public class JavascriptBackend extends AbstractJsBackend  {
       this.appSections = appSections;
     }
 
-    /**
-     * @return the charsWritten
-     */
-    public long getCharsWritten() {
-      return charsWritten;
-    }
-
-    /**
-     * @return the nativeCharsWritten
-     */
-    public long getNativeCharsWritten() {
-      return nativeCharsWritten;
-    }
-
     @Override
     public void visitNative(LibraryUnit libUnit, LibraryNode node)
         throws IOException {
       DartSource nativeSrc = libUnit.getSource().getSourceFor(node.getText());
       Reader r = nativeSrc.getSourceReader();
       long charsWrittenForFile = CharStreams.copy(r, out);
-      nativeCharsWritten += charsWrittenForFile;
-      charsWritten += charsWrittenForFile;
     }
 
     @Override
@@ -136,7 +119,6 @@ public class JavascriptBackend extends AbstractJsBackend  {
       boolean failed = true;
       try {
         partSize = CharStreams.copy(r, out);
-        charsWritten += partSize;
         failed = false;
       } finally {
         Closeables.close(r, failed);
@@ -158,12 +140,6 @@ public class JavascriptBackend extends AbstractJsBackend  {
 
     DepsWritingCallback callback = new DepsWritingCallback(context, out, appSections);
     DependencyBuilder.build(context.getAppLibraryUnit(), callback);
-
-    CompilerMetrics compilerMetrics = context.getCompilerMetrics();
-    if (compilerMetrics != null) {
-      compilerMetrics.packagedJsApplication(
-          callback.getCharsWritten(), callback.getNativeCharsWritten());
-    }
   }
 
   @Override
@@ -172,8 +148,13 @@ public class JavascriptBackend extends AbstractJsBackend  {
                          DartCompilerContext context,
                          CoreTypeProvider typeProvider)
       throws IOException {
+    
+    LibraryUnit appLibraryUnit = context.getAppLibraryUnit();
+    boolean hasEntryPoint = appLibraryUnit.getElement().getEntryPoint() != null;
+    
     List<SourceMapSection> appSections = Lists.newArrayList();
-    Writer out = context.getArtifactWriter(app, "", EXTENSION_APP_JS);
+    String completeArtifactName = EXTENSION_APP_JS + ".complete";
+    Writer out = context.getArtifactWriter(app, "", completeArtifactName);
     boolean failed = true;
     try {
       // Emit the concatenated Javascript sources in dependency order.
@@ -184,7 +165,30 @@ public class JavascriptBackend extends AbstractJsBackend  {
     } finally {
       Closeables.close(out, failed);
     }
+    
+    long fileSize = computeCompleteArtifactSize(app, context, completeArtifactName);
+    Reader artifactReader = context.getArtifactReader(app, "", completeArtifactName);
+    Writer artifactWriter = context.getArtifactWriter(app, "", EXTENSION_APP_JS);
+    try {
+      failed = true;
+      long outputFileSize;
+      if (hasEntryPoint) {
+        outputFileSize = TreeShaker.reduce(artifactReader, artifactWriter, fileSize);
+      } else {
+        outputFileSize = CharStreams.copy(artifactReader, artifactWriter);

[fabiomfv, 2011/12/01 15:37:40]

could we just rename(move) the file instead of copying in this case? basically
we would only use the completeArtifact in case it has an entrypoint.

[mmendez, 2011/12/01 21:31:30]

I can't rename with the current API, but what I will do is to just write into
the final name if we don't have an entry point.

On 2011/12/01 15:37:40, fabiomfv wrote:

+      }
+      failed = false;
+      
+      CompilerMetrics compilerMetrics = context.getCompilerMetrics();
+      if (compilerMetrics != null) {
+        compilerMetrics.packagedJsApplication(outputFileSize, -1);
+      }
 
+    } finally {
+      Closeables.close(artifactWriter, failed);
+      Closeables.close(artifactReader, failed);
+    }
+    
     Writer srcMapOut = context.getArtifactWriter(app, "", EXTENSION_APP_JS_SRC_MAP);
     failed = true;
     try {
@@ -198,6 +202,19 @@ public class JavascriptBackend extends AbstractJsBackend  {
     }
   }
 
+  private static long computeCompleteArtifactSize(LibrarySource app, DartCompilerContext context,
+      String completeArtifactName) throws IOException {
+    Reader artifactReader = context.getArtifactReader(app, "", completeArtifactName);
+    boolean failed = true;
+    try {
+      long fileSize = artifactReader.skip(Long.MAX_VALUE);
+      failed = false;
+      return fileSize;
+    } finally {
+      Closeables.close(artifactReader, failed);
+    }
+  }
+
   @Override
   public String getAppExtension() {
     return EXTENSION_APP_JS;