Use file hash to check for file changes before transpiling (reactjs#299) (reactjs#313)

* Use file hash to check for file changes before transpiling (reactjs#299)

* Add .editorconfig file

* Add check for file hash check (reactjs#299)

* Remove debug File.WriteAllText from test.

* Fix erroneous comment in babel.cs

Author: TorbenRahbekKoch

src/.editorconfig

@@ -0,0 +1,13 @@
+# editorconfig.org
+root = true
+
+[*]
+charset = utf-8
+end_of_line = crlf
+indent_size = 4
+indent_style = tab
+insert_final_newline = true
+
+[*.json]
+indent_size = 2
+indent_style = space

src/React.Core/Babel.cs

@@ -350,12 +350,37 @@ string filename
 		)
 		{
 			var outputPath = GetOutputPath(filename);
-			var sourceMapPath = GetSourceMapOutputPath(filename);
 			var contents = _fileSystem.ReadAsString(filename);
+			if (CacheIsValid(contents, outputPath))
+				return outputPath;
+			
 			var result = TransformWithHeader(filename, contents, null);
+
+			var sourceMapPath = GetSourceMapOutputPath(filename);
 			_fileSystem.WriteAsString(outputPath, result.Code);
-			_fileSystem.WriteAsString(sourceMapPath, result.SourceMap == null ? string.Empty : result.SourceMap.ToJson());
+			_fileSystem.WriteAsString(sourceMapPath, result.SourceMap == null ? string.Empty : result.SourceMap.ToJson());                
+			
 			return outputPath;
 		}
+
+		/// <summary>
+		/// Checks whether an input file (given as inputFileContents) should be transpiled
+		/// by calculating the hash and comparing it to the hash value stored
+		/// in the file given by outputPath. If the outputPath file does not
+		/// exist the input file should always be transpiled.
+		/// </summary>
+		/// <param name="inputFileContents">The contents of the input file.</param>
+		/// <param name="outputPath">The output path of the (possibly previously) generated file.</param>
+		/// <returns>Returns false if the file should be transpiled, true otherwise.</returns>
+		public virtual bool CacheIsValid(string inputFileContents, string outputPath)
+		{            
+			if (!_fileSystem.FileExists(outputPath))
+				return false;
+
+			var hashForInputFile = _fileCacheHash.CalculateHash(inputFileContents);
+			var existingOutputContents = _fileSystem.ReadAsString(outputPath);
+			var fileHasNotChanged = _fileCacheHash.ValidateHash(existingOutputContents, hashForInputFile);
+			return fileHasNotChanged;
+		}
 	}
 }

src/React.Tests/Core/BabelTransformerTests.cs

@@ -32,6 +32,10 @@ public void SetUp()
 			_fileSystem = new Mock<IFileSystem>();
 			_fileSystem.Setup(x => x.MapPath(It.IsAny<string>())).Returns<string>(x => x);
 
+			// Per default the output file should not exist, then individual tests
+			// can choose otherwise.
+			_fileSystem.Setup(x => x.FileExists(It.IsAny<string>())).Returns(false);
+
 			_fileCacheHash = new Mock<IFileCacheHash>();
 
 			_babel = new Babel(
@@ -152,6 +156,29 @@ public void ShouldSaveTransformationResult()
 			StringAssert.EndsWith("React.DOM.div('Hello World')", result);
 		}
 
+		[Test]
+		public void ShouldSkipTransformationIfCacheIsValid()
+		{
+			_fileSystem.Setup(x => x.ReadAsString("foo.jsx")).Returns("<div>Hello World</div>");
+			_fileSystem.Setup(x => x.FileExists(It.IsAny<string>())).Returns(true);
+			_fileCacheHash.Setup(x => x.ValidateHash(It.IsAny<string>(), It.IsAny<string>())).Returns(true);
+			_environment.Setup(x => x.ExecuteWithBabel<JavaScriptWithSourceMap>(
+				"ReactNET_transform_sourcemap",
+				It.IsAny<string>(),
+				It.IsAny<string>(), // Babel config
+				"foo.jsx" // File name
+			)).Returns(new JavaScriptWithSourceMap { Code = "React.DOM.div('Hello World')" });
+
+			string result = null;
+			_fileSystem.Setup(x => x.WriteAsString("foo.generated.js", It.IsAny<string>())).Callback(
+				(string filename, string contents) => result = contents
+			);
+
+			var resultFilename = _babel.TransformAndSaveFile("foo.jsx");
+			Assert.AreEqual("foo.generated.js", resultFilename);
+			Assert.IsNull(result, "There should be no result. Cached result should have been used.");
+		}
+
 		private void SetUpEmptyCache()
 		{
 			_cache.Setup(x => x.Get<JavaScriptWithSourceMap>("JSX_v3_foo.jsx", null)).Returns((JavaScriptWithSourceMap)null);