Don't calculate checksum in design time mode

src/Microsoft.AspNet.Razor/RazorTemplateEngine.cs

@@ -176,21 +176,27 @@ namespace Microsoft.AspNet.Razor
                                              string sourceFileName)
         {
             MemoryStream memoryStream = null;
+            string checksum = null;
             try
             {
-                if (!inputStream.CanSeek)
+                if (!Host.DesignTimeMode)
                 {
-                    memoryStream = new MemoryStream();
+                    // We don't need to calculate the checksum in design time.
-                    inputStream.CopyTo(memoryStream);
 
-                    // We don't have to dispose the input stream since it is owned externally.
+                    if (!inputStream.CanSeek)
-                    inputStream = memoryStream;
+                    {
+                        memoryStream = new MemoryStream();
+                        inputStream.CopyTo(memoryStream);
+
+                        // We don't have to dispose the input stream since it is owned externally.
+                        inputStream = memoryStream;
+                    }
+
+                    inputStream.Position = 0;
+                    checksum = ComputeChecksum(inputStream);
+                    inputStream.Position = 0;
                 }
 
-                inputStream.Position = 0;
-                var checksum = ComputeChecksum(inputStream);
-                inputStream.Position = 0;
-
                 using (var reader = new StreamReader(inputStream,
                                                      Encoding.UTF8,
                                                      detectEncodingFromByteOrderMarks: true,

test/Microsoft.AspNet.Razor.Test/RazorTemplateEngineTest.cs

@@ -239,7 +239,7 @@ namespace Microsoft.AspNet.Razor.Test
 
         [Theory]
         [MemberData(nameof(GenerateCodeCalculatesLinePragma_IfStreamInputIsUsedData))]
-        public void GenerateCodeCalculatesLinePragma_IfStreamInputIsUsed(Stream stream)
+        public void GenerateCodeCalculatesChecksum_IfStreamInputIsUsed(Stream stream)
         {
             // Arrange
             var engine = new TestableRazorTemplateEngine();
@@ -251,6 +251,20 @@ namespace Microsoft.AspNet.Razor.Test
             Assert.Equal("7b502c3a1f48c8609ae212cdfb639dee39673f5e", engine.Checksum);
         }
 
+        [Fact]
+        public void GenerateCode_DoesNotCalculateChecksum_InDesignTimeMode()
+        {
+            // Arrange
+            var engine = new TestableRazorTemplateEngine();
+            engine.Host.DesignTimeMode = true;
+
+            // Act
+            var results = engine.GenerateCode(Stream.Null, "some-class", "some-ns", "foo.cshtml");
+
+            // Assert
+            Assert.Null(engine.Checksum);
+        }
+
         private static RazorEngineHost CreateHost(bool designTime = false)
         {
             return new RazorEngineHost(new CSharpRazorCodeLanguage())
@@ -264,7 +278,6 @@ namespace Microsoft.AspNet.Razor.Test
             public TestableRazorTemplateEngine()
                 : base(CreateHost())
             {
-
             }
 
             public string Checksum { get; set; }