JS tree shaking for incremental builds.

compiler/javatests/com/google/dart/compiler/backend/js/analysis/TreeShakerTest.java

Index: compiler/javatests/com/google/dart/compiler/backend/js/analysis/TreeShakerTest.java
diff --git a/compiler/javatests/com/google/dart/compiler/backend/js/analysis/TreeShakerTest.java b/compiler/javatests/com/google/dart/compiler/backend/js/analysis/TreeShakerTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..543ca4fa9f29940d084daa5a3e2458d9612ec369
--- /dev/null
+++ b/compiler/javatests/com/google/dart/compiler/backend/js/analysis/TreeShakerTest.java
@@ -0,0 +1,73 @@
+// Copyright 2011 Google Inc. All Rights Reserved.
+
+package com.google.dart.compiler.backend.js.analysis;
+
+import com.google.dart.compiler.DartCompilerContext;
+import com.google.dart.compiler.LibrarySource;
+import com.google.dart.compiler.MockLibrarySource;
+import com.google.dart.compiler.Source;
+import com.google.dart.compiler.testing.TestCompilerContext;
+
+import junit.framework.TestCase;
+
+import java.io.IOException;
+import java.io.Reader;
+import java.io.StringReader;
+import java.io.StringWriter;
+import java.io.Writer;
+
+/**
+ * Tests the JS based tree shaker used in incremental compilation.
+ */
+public class TreeShakerTest extends TestCase {
+  class MockCompilerContext extends TestCompilerContext {
+    private final String srcCode;
+
+    public MockCompilerContext(String srcCode) {
+      this.srcCode = srcCode;
+    }
+
+    @Override
+    public Reader getArtifactReader(Source source, String part, String extension) {
+      return new StringReader(srcCode);
+    }
+  }
+
+  /**
+   * Tests that {@link TreeShaker#reduce(LibrarySource, DartCompilerContext, String, Writer)} can
+   * remove unused methods.
+   */
+  public void testReduce() throws IOException {
+    StringBuffer inputSrc = new StringBuffer();
+    inputSrc.append("function A() {}\n");
+    inputSrc.append("A.prototype.foo = function(){}\n");
+    inputSrc.append("function B() {}\n");
+    inputSrc.append("B.prototype.foo = function(){}\n");
+    inputSrc.append("function C() { A(); }\n");
+    inputSrc.append("RunEntry(C);\n");
+
+    StringWriter outputCode = new StringWriter();
+
+    TreeShaker.reduce(new MockLibrarySource(), new MockCompilerContext(inputSrc.toString()), "",
+        outputCode);
+
+    StringBuffer outputSrc = new StringBuffer();
+    outputSrc.append("function A() {}\n");
+    outputSrc.append("function C() { A(); }\n");
+    outputSrc.append("RunEntry(C);\n");
+
+    assertEquals(outputSrc.toString(), outputCode.toString());
+  }
+
+  /**
+   * Tests that {@link TreeShaker#reduce(LibrarySource, DartCompilerContext, String, Writer)} can 
+   * handle empty code.
+   */
+  public void testReduceEmpty() throws IOException {
+    StringReader inputSrc = new StringReader("");
+    StringWriter outputSrc = new StringWriter();
+    TreeShaker.reduce(new MockLibrarySource(), new MockCompilerContext(""), "", outputSrc);
+    
+    assertEquals("", outputSrc.toString());
+  }
+}