Adding contract interfaces for specifying runtime compilation exceptions.

Fixes #12

Author: pranavkm

src/Microsoft.AspNet.Diagnostics/Compilation/ICompilationException.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using Microsoft.Framework.Runtime;
+
+namespace Microsoft.AspNet.Diagnostics
+{
+    /// <summary>
+    /// Specifies the contract for an exception representing compilation failure.
+    /// </summary>
+    [AssemblyNeutral]
+    public interface ICompilationException
+    {
+        /// <summary>
+        /// Gets a sequence of <see cref="ICompilationFailure"/> with compilation failures.
+        /// </summary>
+        IEnumerable<ICompilationFailure> CompilationFailures { get; }
+    }
+}

src/Microsoft.AspNet.Diagnostics/Compilation/ICompilationFailure.cs

@@ -0,0 +1,40 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using Microsoft.Framework.Runtime;
+
+namespace Microsoft.AspNet.Diagnostics
+{
+    /// <summary>
+    /// Specifies the contract for a file that fails compilation.
+    /// </summary>
+    [AssemblyNeutral]
+    public interface ICompilationFailure
+    {
+        /// <summary>
+        /// Path of the file that produced the compilation exception.
+        /// </summary>
+        string SourceFilePath { get; }
+
+        /// <summary>
+        /// Contents of the file.
+        /// </summary>
+        string SourceFileContent { get; }
+
+        /// <summary>
+        /// Contents being compiled.
+        /// </summary>
+        /// <remarks>
+        /// For templated files, the <see cref="SourceFileContent"/> represents the original content and
+        /// <see cref="CompiledContent"/> represents the transformed content. This property can be null if
+        /// the exception is encountered during transformation.
+        /// </remarks>
+        string CompiledContent { get; }
+
+        /// <summary>
+        /// Gets a sequence of <see cref="ICompilationMessage"/> produced as a result of compilation.
+        /// </summary>
+        IEnumerable<ICompilationMessage> Messages { get; }
+    }
+}

src/Microsoft.AspNet.Diagnostics/Compilation/ICompilationMessage.cs

@@ -0,0 +1,40 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.Framework.Runtime;
+
+namespace Microsoft.AspNet.Diagnostics
+{
+    /// <summary>
+    /// Specifies the contract for diagnostic messages produced as result of compiling an instance
+    /// of <see cref="ICompilationFailure"/>.
+    /// </summary>
+    [AssemblyNeutral]
+    public interface ICompilationMessage
+    {
+        /// <summary>
+        /// Gets the error message.
+        /// </summary>
+        string Message { get; }
+
+        /// <summary>
+        /// Gets the zero-based line index for the start of the compilation error.
+        /// </summary>
+        int StartLine { get; }
+
+        /// <summary>
+        /// Gets the zero-based column index for the start of the compilation error.
+        /// </summary>
+        int StartColumn { get; }
+
+        /// <summary>
+        /// Gets the zero-based line index for the end of the compilation error.
+        /// </summary>
+        int EndLine { get; }
+
+        /// <summary>
+        /// Gets the zero-based column index for the end of the compilation error.
+        /// </summary>
+        int EndColumn { get; }
+    }
+}

src/Microsoft.AspNet.Diagnostics/ErrorPageMiddleware.cs

@@ -76,7 +76,70 @@ public async Task Invoke(HttpContext context)
         }
 
         // Assumes the response headers have not been sent.  If they have, still attempt to write to the body.
-        private async Task DisplayException(HttpContext context, Exception ex)
+        private Task DisplayException(HttpContext context, Exception ex)
+        {
+            var compilationException = ex as ICompilationException;
+            if (compilationException != null)
+            {
+                return DisplayCompilationException(context, ex, compilationException);
+            }
+
+            return DisplayRuntimeException(context, ex);
+        }
+
+        private Task DisplayCompilationException(HttpContext context,
+                                                 Exception ex,
+                                                 ICompilationException compilationException)
+        {
+            var stackFrames = new List<StackFrame>();
+            var model = new CompilationErrorPageModel()
+            {
+                Options = _options,
+                ErrorDetails = new ErrorDetails
+                {
+                    Error = ex,
+                    StackFrames = stackFrames
+                }
+            };
+
+            // For view compilation, the most common case is to stop at the first failing file compiled as part of
+            // rendering a view. Consequently we'll limit ourselves to displaying errors from the first failure.
+            var failedCompilationFile = compilationException.CompilationFailures.FirstOrDefault();
+            if (failedCompilationFile != null)
+            {
+                var fileContent = failedCompilationFile.SourceFileContent
+                                                       .Split(new[] { Environment.NewLine }, StringSplitOptions.None);
+
+                foreach (var item in failedCompilationFile.Messages)
+                {
+                    // Convert 0-based line indexes to 1-based index that the StackFrame expects
+                    var lineIndex = item.StartLine + 1;
+                    var frame = new StackFrame
+                    {
+                        File = failedCompilationFile.SourceFilePath,
+                        Line = lineIndex,
+                        Function = string.Empty
+                    };
+
+                    if (_options.ShowSourceCode)
+                    {
+                        ReadFrameContent(frame, fileContent, lineIndex, item.EndLine + 1);
+                        frame.ErrorDetails = item.Message;
+                    }
+
+                    stackFrames.Add(frame);
+                }
+            }
+
+            var errorPage = new CompilationErrorPage
+            {
+                Model = model
+            };
+
+            return errorPage.ExecuteAsync(context);
+        }
+
+        private Task DisplayRuntimeException(HttpContext context, Exception ex)
         {
             var request = context.Request;
 
@@ -107,7 +170,7 @@ private async Task DisplayException(HttpContext context, Exception ex)
             }*/
 
             var errorPage = new ErrorPage(model);
-            await errorPage.ExecuteAsync(context);
+            return errorPage.ExecuteAsync(context);
         }
 
         private IEnumerable<ErrorDetails> GetErrorDetails(Exception ex, bool showSource)
@@ -160,14 +223,22 @@ private StackFrame LoadFrame(string function, string file, int lineNumber, bool
             if (showSource && File.Exists(file))
             {
                 IEnumerable<string> code = File.ReadLines(file);
-                frame.PreContextLine = Math.Max(lineNumber - _options.SourceCodeLineCount, 1);
-                frame.PreContextCode = code.Skip(frame.PreContextLine - 1).Take(lineNumber - frame.PreContextLine).ToArray();
-                frame.ContextCode = code.Skip(lineNumber - 1).FirstOrDefault();
-                frame.PostContextCode = code.Skip(lineNumber).Take(_options.SourceCodeLineCount).ToArray();
+                ReadFrameContent(frame, code, lineNumber, lineNumber);
             }
             return frame;
         }
 
+        private void ReadFrameContent(StackFrame frame,
+                                      IEnumerable<string> code,
+                                      int startLineNumber,
+                                      int endLineNumber)
+        {
+            frame.PreContextLine = Math.Max(startLineNumber - _options.SourceCodeLineCount, 1);
+            frame.PreContextCode = code.Skip(frame.PreContextLine - 1).Take(startLineNumber - frame.PreContextLine).ToArray();
+            frame.ContextCode = code.Skip(startLineNumber - 1).Take(1 + Math.Max(0, endLineNumber - startLineNumber));
+            frame.PostContextCode = code.Skip(startLineNumber).Take(_options.SourceCodeLineCount).ToArray();
+        }
+
         internal class Chunk
         {
             public string Text { get; set; }

src/Microsoft.AspNet.Diagnostics/Properties/Resources.Designer.cs

@@ -230,4 +230,7 @@
   <data name="WelcomeTitle" xml:space="preserve">
     <value>Your ASP.NET vNext application has been successfully started.</value>
   </data>
+  <data name="ErrorPageHtml_CompilationException" xml:space="preserve">
+    <value>An error occurred during the compilation of a resource required to process this request. Please review the following specific error details and modify your source code appropriately.</value>
+  </data>
 </root>

src/Microsoft.AspNet.Diagnostics/Resources.resx

@@ -0,0 +1,23 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+
+namespace Microsoft.AspNet.Diagnostics.Views
+{
+    /// <summary>
+    /// Holds data to be displayed on the compilation error page.
+    /// </summary>
+    public class CompilationErrorPageModel
+    {
+        /// <summary>
+        /// Options for what output to display.
+        /// </summary>
+        public ErrorPageOptions Options { get; set; }
+
+        /// <summary>
+        /// Detailed information about each parse or compilation error.
+        /// </summary>
+        public ErrorDetails ErrorDetails { get; set; }
+    }
+}