External functions in razor view

Fixes #809

src/Microsoft.AspNetCore.Mvc.Razor.Host/IMvcRazorHostWithCodeGenerationContext.cs

@@ -0,0 +1,20 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Razor;
+using Microsoft.AspNetCore.Razor.CodeGenerators;
+
+namespace Microsoft.AspNetCore.Mvc.Razor
+{
+    /// <summary>
+    /// Specifies the contracts for a Razor host that parses Razor files and generates C# code.
+    /// </summary>
+    public interface IMvcRazorHostWithTemplateEngineContext
+    {
+        /// <summary>
+        /// Parses and generates the contents of a Razor file.
+        /// </summary>
+        /// <returns>The <see cref="GeneratorResults"/>.</returns>
+        GeneratorResults GenerateCode(TemplateEngineContext context);
+    }
+}

src/Microsoft.AspNetCore.Mvc.Razor.Host/MvcRazorHost.cs

@@ -6,6 +6,7 @@
 using System.IO;
 using System.Linq;
 using Microsoft.AspNetCore.Mvc.Razor.Directives;
+using Microsoft.AspNetCore.Mvc.Razor.Host;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Razor;
 using Microsoft.AspNetCore.Razor.Chunks;
@@ -20,7 +21,7 @@
 
 namespace Microsoft.AspNetCore.Mvc.Razor
 {
-    public class MvcRazorHost : RazorEngineHost, IMvcRazorHost
+    public class MvcRazorHost : RazorEngineHost, IMvcRazorHost, IMvcRazorHostWithTemplateEngineContext
     {
         private const string BaseType = "Microsoft.AspNetCore.Mvc.Razor.RazorPage";
         private const string HtmlHelperPropertyName = "Html";
@@ -118,7 +119,7 @@ internal MvcRazorHost(IChunkTreeCache chunkTreeCache, RazorPathNormalizer pathNo
                     TagHelperOutputContentPropertyName = nameof(TagHelperOutput.Content),
                     ExecutionContextSetOutputContentAsyncMethodName = nameof(TagHelperExecutionContext.SetOutputContentAsync),
                     TagHelperAttributeValuePropertyName = nameof(TagHelperAttribute.Value),
-        })
+                })
             {
                 BeginContextMethodName = "BeginContext",
                 EndContextMethodName = "EndContext"
@@ -285,6 +286,23 @@ public GeneratorResults GenerateCode(string rootRelativePath, Stream inputStream
             return engine.GenerateCode(inputStream, className, DefaultNamespace, rootRelativePath);
         }
 
+        /// <inheritdoc />
+        public GeneratorResults GenerateCode(TemplateEngineContext context)
+        {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (string.IsNullOrEmpty(context.ClassName) && !string.IsNullOrEmpty(context.RelativePath))
+            {
+                context.ClassName = ParserHelpers.SanitizeClassName(context.RelativePath);
+            }
+
+            var engine = new RazorTemplateEngine(this);
+            return engine.GenerateCode(context);
+        }
+
         /// <inheritdoc />
         public override RazorParser DecorateRazorParser(RazorParser razorParser, string sourceFileName)
         {
@@ -297,6 +315,33 @@ public override RazorParser DecorateRazorParser(RazorParser razorParser, string
             return new MvcRazorParser(razorParser, inheritedChunkTrees, DefaultInheritedChunks, ModelExpressionType);
         }
 
+        public override RazorParser DecorateRazorParser(
+            RazorParser incomingRazorParser,
+            TemplateEngineContext context)
+        {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (incomingRazorParser == null)
+            {
+                throw new ArgumentNullException(nameof(incomingRazorParser));
+            }
+
+            if (string.IsNullOrEmpty(context.RelativePath))
+            {
+                throw new ArgumentException(Resources.ArgumentCannotBeNullOrEmpy, nameof(context.RelativePath));
+            }
+
+            var inheritedChunkTrees = GetInheritedChunkTrees(context.RelativePath);
+            return new MvcRazorParser(
+                incomingRazorParser,
+                inheritedChunkTrees,
+                DefaultInheritedChunks,
+                ModelExpressionType);
+        }
+
         /// <inheritdoc />
         public override ParserBase DecorateCodeParser(ParserBase incomingCodeParser)
         {

src/Microsoft.AspNetCore.Mvc.Razor/Internal/DefaultRoslynCompilationService.cs

@@ -135,7 +135,7 @@ public CompilationResult Compile(RelativeFileInfo fileInfo, string compilationCo
                     if (!result.Success)
                     {
                         return GetCompilationFailedResult(
-                            fileInfo.RelativePath,
+                            fileInfo,
                             compilationContent,
                             assemblyName,
                             result.Diagnostics);
@@ -201,14 +201,14 @@ private CSharpCompilation Rewrite(CSharpCompilation compilation)
 
         // Internal for unit testing
         internal CompilationResult GetCompilationFailedResult(
-            string relativePath,
+            RelativeFileInfo fileInfo,
             string compilationContent,
             string assemblyName,
             IEnumerable<Diagnostic> diagnostics)
         {
             var diagnosticGroups = diagnostics
                 .Where(IsError)
-                .GroupBy(diagnostic => GetFilePath(relativePath, diagnostic), StringComparer.Ordinal);
+                .GroupBy(diagnostic => GetFilePath(fileInfo.RelativePath, diagnostic), StringComparer.Ordinal);
 
             var failures = new List<CompilationFailure>();
             foreach (var group in diagnosticGroups)
@@ -223,7 +223,7 @@ private CSharpCompilation Rewrite(CSharpCompilation compilation)
                 }
                 else
                 {
-                    sourceFileContent = ReadFileContentsSafely(_fileProvider, sourceFilePath);
+                    sourceFileContent = ReadFileContentsSafely(fileInfo.FileInfo);
                 }
 
                 string additionalMessage = null;
@@ -265,9 +265,8 @@ private static bool IsError(Diagnostic diagnostic)
             return diagnostic.IsWarningAsError || diagnostic.Severity == DiagnosticSeverity.Error;
         }
 
-        private static string ReadFileContentsSafely(IFileProvider fileProvider, string filePath)
+        private static string ReadFileContentsSafely(IFileInfo fileInfo)
         {
-            var fileInfo = fileProvider.GetFileInfo(filePath);
             if (fileInfo.Exists)
             {
                 try

src/Microsoft.AspNetCore.Mvc.Razor/Internal/RazorCompilationService.cs

@@ -8,7 +8,6 @@
 using System.Linq;
 using Microsoft.AspNetCore.Diagnostics;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
-using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Razor;
 using Microsoft.AspNetCore.Razor.CodeGenerators;
 using Microsoft.Extensions.FileProviders;
@@ -23,6 +22,7 @@ public class RazorCompilationService : IRazorCompilationService
     {
         private readonly ICompilationService _compilationService;
         private readonly IMvcRazorHost _razorHost;
+        private readonly IMvcRazorHostWithTemplateEngineContext _razorHostWithContext;
         private readonly IFileProvider _fileProvider;
         private readonly ILogger _logger;
 
@@ -41,6 +41,7 @@ public class RazorCompilationService : IRazorCompilationService
         {
             _compilationService = compilationService;
             _razorHost = razorHost;
+            _razorHostWithContext = razorHost as IMvcRazorHostWithTemplateEngineContext;
             _fileProvider = fileProviderAccessor.FileProvider;
             _logger = loggerFactory.CreateLogger<RazorCompilationService>();
         }
@@ -53,16 +54,29 @@ public CompilationResult Compile(RelativeFileInfo file)
                 throw new ArgumentNullException(nameof(file));
             }
 
+            var filePath = file.FileInfo.PhysicalPath ?? file.RelativePath;
             GeneratorResults results;
             using (var inputStream = file.FileInfo.CreateReadStream())
             {
-                _logger.RazorFileToCodeCompilationStart(file.RelativePath);
+                _logger.RazorFileToCodeCompilationStart(filePath);
 
                 var startTimestamp = _logger.IsEnabled(LogLevel.Debug) ? Stopwatch.GetTimestamp() : 0;
 
-                results = GenerateCode(file.RelativePath, inputStream);
+                if (_razorHostWithContext != null)
+                {
+                    var context = new TemplateEngineContext(inputStream, filePath)
+                    {
+                        RelativePath = file.RelativePath,
+                    };
+
+                    results = _razorHostWithContext.GenerateCode(context);
+                }
+                else
+                {
+                    results = _razorHost.GenerateCode(filePath, inputStream);
+                }
 
-                _logger.RazorFileToCodeCompilationEnd(file.RelativePath, startTimestamp);
+                _logger.RazorFileToCodeCompilationEnd(filePath, startTimestamp);
             }
 
             if (!results.Success)
@@ -73,36 +87,21 @@ public CompilationResult Compile(RelativeFileInfo file)
             return _compilationService.Compile(file, results.GeneratedCode);
         }
 
-        /// <summary>
-        /// Generate code for the Razor file at <paramref name="relativePath"/> with content
-        /// <paramref name="inputStream"/>.
-        /// </summary>
-        /// <param name="relativePath">
-        /// The path of the Razor file relative to the root of the application. Used to generate line pragmas and
-        /// calculate the class name of the generated type.
-        /// </param>
-        /// <param name="inputStream">A <see cref="Stream"/> that contains the Razor content.</param>
-        /// <returns>A <see cref="GeneratorResults"/> instance containing results of code generation.</returns>
-        protected virtual GeneratorResults GenerateCode(string relativePath, Stream inputStream)
-        {
-            return _razorHost.GenerateCode(relativePath, inputStream);
-        }
-
         // Internal for unit testing
         internal CompilationResult GetCompilationFailedResult(RelativeFileInfo file, IEnumerable<RazorError> errors)
         {
             // If a SourceLocation does not specify a file path, assume it is produced
             // from parsing the current file.
             var messageGroups = errors
-                .GroupBy(razorError =>
-                razorError.Location.FilePath ?? file.RelativePath,
-                StringComparer.Ordinal);
+                .GroupBy(
+                    razorError => razorError.Location.FilePath ?? file.RelativePath,
+                    StringComparer.Ordinal);
 
             var failures = new List<CompilationFailure>();
             foreach (var group in messageGroups)
             {
                 var filePath = group.Key;
-                var fileContent = ReadFileContentsSafely(filePath);
+                var fileContent = ReadFileContentsSafely(file.FileInfo);
                 var compilationFailure = new CompilationFailure(
                     filePath,
                     fileContent,
@@ -127,9 +126,8 @@ private DiagnosticMessage CreateDiagnosticMessage(RazorError error, string fileP
                 endColumn: error.Location.CharacterIndex + error.Length);
         }
 
-        private string ReadFileContentsSafely(string relativePath)
+        private string ReadFileContentsSafely(IFileInfo fileInfo)
         {
-            var fileInfo = _fileProvider.GetFileInfo(relativePath);
             if (fileInfo.Exists)
             {
                 try