Capture exceptions when trying to parse files and return parse errors.

#808

src/Microsoft.AspNetCore.Razor/RazorResources.resx

@@ -428,4 +428,7 @@ Instead, wrap the contents of the block in "{{}}":
   <data name="ParseError_IncompleteQuotesAroundDirective" xml:space="preserve">
     <value>Optional quote around the directive '{0}' is missing the corresponding opening or closing quote.</value>
   </data>
+  <data name="FatalException" xml:space="preserve">
+    <value>A fatal exception occurred when trying to parse '{0}':{1}{2}</value>
+  </data>
 </root>

src/Microsoft.AspNetCore.Razor/RazorTemplateEngine.cs

@@ -2,14 +2,19 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Security.Cryptography;
 using System.Text;
 using System.Threading;
+using Microsoft.AspNetCore.Razor.Chunks;
 using Microsoft.AspNetCore.Razor.Chunks.Generators;
 using Microsoft.AspNetCore.Razor.CodeGenerators;
+using Microsoft.AspNetCore.Razor.Compilation.TagHelpers;
 using Microsoft.AspNetCore.Razor.Parser;
+using Microsoft.AspNetCore.Razor.Parser.SyntaxTree;
 using Microsoft.AspNetCore.Razor.Text;
 
 namespace Microsoft.AspNetCore.Razor
@@ -363,26 +368,50 @@ protected internal virtual GeneratorResults GenerateCodeCore(
                 throw new ArgumentNullException(nameof(input));
             }
 
-            className = (className ?? Host.DefaultClassName) ?? DefaultClassName;
-            rootNamespace = (rootNamespace ?? Host.DefaultNamespace) ?? DefaultNamespace;
-
-            // Run the parser
-            var parser = CreateParser(sourceFileName);
-            Debug.Assert(parser != null);
-            var results = parser.Parse(input);
-
-            // Generate code
-            var chunkGenerator = CreateChunkGenerator(className, rootNamespace, sourceFileName);
-            chunkGenerator.DesignTimeMode = Host.DesignTimeMode;
-            chunkGenerator.Visit(results);
-
-            var codeGeneratorContext = new CodeGeneratorContext(chunkGenerator.Context, results.ErrorSink);
-            codeGeneratorContext.Checksum = checksum;
-            var codeGenerator = CreateCodeGenerator(codeGeneratorContext);
-            var codeGeneratorResult = codeGenerator.Generate();
-
-            // Collect results and return
-            return new GeneratorResults(results, codeGeneratorResult, codeGeneratorContext.ChunkTreeBuilder.Root);
+            try
+            {
+                className = (className ?? Host.DefaultClassName) ?? DefaultClassName;
+                rootNamespace = (rootNamespace ?? Host.DefaultNamespace) ?? DefaultNamespace;
+
+                // Run the parser
+                var parser = CreateParser(sourceFileName);
+                Debug.Assert(parser != null);
+                var results = parser.Parse(input);
+
+                // Generate code
+                var chunkGenerator = CreateChunkGenerator(className, rootNamespace, sourceFileName);
+                chunkGenerator.DesignTimeMode = Host.DesignTimeMode;
+                chunkGenerator.Visit(results);
+
+                var codeGeneratorContext = new CodeGeneratorContext(chunkGenerator.Context, results.ErrorSink);
+                codeGeneratorContext.Checksum = checksum;
+                var codeGenerator = CreateCodeGenerator(codeGeneratorContext);
+                var codeGeneratorResult = codeGenerator.Generate();
+
+                // Collect results and return
+                return new GeneratorResults(results, codeGeneratorResult, codeGeneratorContext.ChunkTreeBuilder.Root);
+            }
+            // During runtime we want code generation explosions to flow up into the calling code. At design time
+            // we want to capture these exceptions to prevent IDEs from crashing.
+            catch (Exception ex) when (Host.DesignTimeMode)
+            {
+                var errorSink = new ErrorSink();
+                errorSink.OnError(
+                    SourceLocation.Undefined,
+                    RazorResources.FormatFatalException(sourceFileName, Environment.NewLine, ex.Message),
+                    length: -1);
+                var emptyBlock = new BlockBuilder();
+                emptyBlock.Type = default(BlockType);
+
+                return new GeneratorResults(
+                    document: emptyBlock.Build(),
+                    tagHelperDescriptors: Enumerable.Empty<TagHelperDescriptor>(),
+                    errorSink: errorSink,
+                    codeGeneratorResult: new CodeGeneratorResult(
+                        code: string.Empty,
+                        designTimeLineMappings: new List<LineMapping>()),
+                    chunkTree: new ChunkTree());
+            }
         }
 
         protected internal virtual RazorChunkGenerator CreateChunkGenerator(

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

@@ -1,6 +1,7 @@
 // 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 System;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;
@@ -18,6 +19,53 @@ namespace Microsoft.AspNetCore.Razor
 {
     public class RazorTemplateEngineTest
     {
+        [Fact]
+        public void InvalidRazorEngineHostReturnsParseErrorsAtDesignTime()
+        {
+            // Arrange
+            var host = new InvalidRazorEngineHost(new CSharpRazorCodeLanguage())
+            {
+                DesignTimeMode = true
+            };
+            var razorEngine = new RazorTemplateEngine(host);
+            var input = new StringTextBuffer("<div>Hello @(\"World\")</div>");
+            var exception = new InvalidOperationException("Hello World");
+            var expectedError = RazorResources.FormatFatalException("test", Environment.NewLine, exception.Message);
+
+            // Act
+            var result = razorEngine.GenerateCode(input, className: null, rootNamespace: null, sourceFileName: "test");
+
+            // Assert
+            Assert.Empty(result.Document.Children);
+            Assert.Empty(result.ChunkTree.Children);
+            Assert.Empty(result.DesignTimeLineMappings);
+            Assert.Empty(result.GeneratedCode);
+
+            var error = Assert.Single(result.ParserErrors);
+            Assert.Equal(expectedError, error.Message, StringComparer.Ordinal);
+            Assert.Equal(SourceLocation.Undefined, error.Location);
+            Assert.Equal(-1, error.Length);
+        }
+
+        [Fact]
+        public void InvalidRazorEngineHostThrowsAtRuntime()
+        {
+            // Arrange
+            var host = new InvalidRazorEngineHost(new CSharpRazorCodeLanguage())
+            {
+                DesignTimeMode = false
+            };
+            var razorEngine = new RazorTemplateEngine(host);
+            var input = new StringTextBuffer("<div>Hello @(\"World\")</div>");
+
+            // Act
+            var thrownException = Assert.Throws<InvalidOperationException>(() =>
+                razorEngine.GenerateCode(input, className: null, rootNamespace: null, sourceFileName: "test"));
+
+            // Assert
+            Assert.Equal("Hello World", thrownException.Message, StringComparer.Ordinal);
+        }
+
         [Fact]
         public void ConstructorInitializesHost()
         {
@@ -339,5 +387,23 @@ protected internal override GeneratorResults GenerateCodeCore(
                 return null;
             }
         }
+
+        private class InvalidRazorEngineHost : RazorEngineHost
+        {
+            public InvalidRazorEngineHost(RazorCodeLanguage codeLanguage) : base(codeLanguage)
+            {
+            }
+
+            public override string DefaultClassName
+            {
+                get
+                {
+                    throw new InvalidOperationException("Hello World");
+                }
+                set
+                {
+                }
+            }
+        }
     }
 }