Add support for optional directives

src/Microsoft.AspNetCore.Razor.Evolution/DirectiveDescriptorBuilder.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;
 
 namespace Microsoft.AspNetCore.Razor.Evolution
@@ -27,6 +28,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution
             private readonly List<DirectiveTokenDescriptor> _tokenDescriptors;
             private readonly string _name;
             private readonly DirectiveDescriptorKind _type;
+            private bool _optional;
 
             public DefaultDirectiveDescriptorBuilder(string name, DirectiveDescriptorKind type)
             {
@@ -39,7 +41,8 @@ namespace Microsoft.AspNetCore.Razor.Evolution
             {
                 var descriptor = new DirectiveTokenDescriptor()
                 {
-                    Kind = DirectiveTokenKind.Type
+                    Kind = DirectiveTokenKind.Type,
+                    Optional = _optional,
                 };
                 _tokenDescriptors.Add(descriptor);
 
@@ -50,7 +53,8 @@ namespace Microsoft.AspNetCore.Razor.Evolution
             {
                 var descriptor = new DirectiveTokenDescriptor()
                 {
-                    Kind = DirectiveTokenKind.Member
+                    Kind = DirectiveTokenKind.Member,
+                    Optional = _optional,
                 };
                 _tokenDescriptors.Add(descriptor);
 
@@ -61,13 +65,26 @@ namespace Microsoft.AspNetCore.Razor.Evolution
             {
                 var descriptor = new DirectiveTokenDescriptor()
                 {
-                    Kind = DirectiveTokenKind.String
+                    Kind = DirectiveTokenKind.String,
+                    Optional = _optional,
                 };
                 _tokenDescriptors.Add(descriptor);
 
                 return this;
             }
 
+            public IDirectiveDescriptorBuilder BeginOptionals()
+            {
+                if (_optional)
+                {
+                    throw new InvalidOperationException(
+                        Resources.FormatDirectiveDescriptor_BeginOptionalsAlreadyInvoked(nameof(BeginOptionals)));
+                }
+
+                _optional = true;
+                return this;
+            }
+
             public DirectiveDescriptor Build()
             {
                 var descriptor = new DirectiveDescriptor

src/Microsoft.AspNetCore.Razor.Evolution/DirectiveTokenDescriptor.cs

@@ -6,5 +6,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution
     public class DirectiveTokenDescriptor
     {
         public DirectiveTokenKind Kind { get; set; }
+
+        public bool Optional { get; set; }
     }
 }

src/Microsoft.AspNetCore.Razor.Evolution/DirectiveTokenDescriptorComparer.cs

@@ -23,7 +23,8 @@ namespace Microsoft.AspNetCore.Razor.Evolution
             }
 
             return descriptorX != null &&
-                descriptorX.Kind == descriptorY.Kind;
+                descriptorX.Kind == descriptorY.Kind &&
+                descriptorX.Optional == descriptorY.Optional;
         }
 
         public int GetHashCode(DirectiveTokenDescriptor descriptor)
@@ -33,7 +34,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution
                 throw new ArgumentNullException(nameof(descriptor));
             }
 
-            return descriptor.Kind.GetHashCode();
+            var hashCodeCombiner = HashCodeCombiner.Start();
+            hashCodeCombiner.Add(descriptor.Kind);
+            hashCodeCombiner.Add(descriptor.Optional ? 1 : 0);
+
+            return hashCodeCombiner.CombinedHash;
         }
     }
 }

src/Microsoft.AspNetCore.Razor.Evolution/IDirectiveDescriptorBuilder.cs

@@ -11,6 +11,8 @@ namespace Microsoft.AspNetCore.Razor.Evolution
 
         IDirectiveDescriptorBuilder AddString();
 
+        IDirectiveDescriptorBuilder BeginOptionals();
+
         DirectiveDescriptor Build();
     }
 }

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/CSharpCodeParser.cs

@@ -83,7 +83,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
         private Dictionary<CSharpKeyword, Action<bool>> _keywordParsers = new Dictionary<CSharpKeyword, Action<bool>>();
 
         public CSharpCodeParser(ParserContext context)
-            : this (directiveDescriptors: Enumerable.Empty<DirectiveDescriptor>(), context: context)
+            : this(directiveDescriptors: Enumerable.Empty<DirectiveDescriptor>(), context: context)
         {
         }
 
@@ -223,7 +223,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
                         // No "@" => Jump straight to AfterTransition
                         AfterTransition();
                     }
-                    
+
                     Output(SpanKind.Code);
                 }
             }
@@ -1507,7 +1507,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
                     Output(SpanKind.Markup, AcceptedCharacters.WhiteSpace);
                 }
 
-                if (EndOfFile)
+                if (tokenDescriptor.Optional && (EndOfFile || At(CSharpSymbolType.NewLine)))
+                {
+                    break;
+                }
+                else if (EndOfFile)
                 {
                     Context.ErrorSink.OnError(
                         CurrentStart,

src/Microsoft.AspNetCore.Razor.Evolution/Properties/Resources.Designer.cs

@@ -186,6 +186,22 @@ namespace Microsoft.AspNetCore.Razor.Evolution
             return GetString("RazorProject_PathMustStartWithForwardSlash");
         }
 
+        /// <summary>
+        /// The method '{0}' has already been invoked.
+        /// </summary>
+        internal static string DirectiveDescriptor_BeginOptionalsAlreadyInvoked
+        {
+            get { return GetString("DirectiveDescriptor_BeginOptionalsAlreadyInvoked"); }
+        }
+
+        /// <summary>
+        /// The method '{0}' has already been invoked.
+        /// </summary>
+        internal static string FormatDirectiveDescriptor_BeginOptionalsAlreadyInvoked(object p0)
+        {
+            return string.Format(CultureInfo.CurrentCulture, GetString("DirectiveDescriptor_BeginOptionalsAlreadyInvoked"), p0);
+        }
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);

src/Microsoft.AspNetCore.Razor.Evolution/Resources.resx

@@ -150,4 +150,7 @@
   <data name="RazorProject_PathMustStartWithForwardSlash" xml:space="preserve">
     <value>Path must begin with a forward slash '/'.</value>
   </data>
+  <data name="DirectiveDescriptor_BeginOptionalsAlreadyInvoked" xml:space="preserve">
+    <value>The method '{0}' has already been invoked.</value>
+  </data>
 </root>

test/Microsoft.AspNetCore.Razor.Evolution.Test/Legacy/CSharpDirectivesTest.cs

@@ -734,6 +734,23 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
                            .Accepts(AcceptedCharacters.None)));
         }
 
+        [Fact]
+        public void OptionalDirectiveTokens_AreSkipped()
+        {
+            // Arrange
+            var descriptor = DirectiveDescriptorBuilder.Create("custom").BeginOptionals().AddString().Build();
+
+            // Act & Assert
+            ParseCodeBlockTest(
+                "@custom ",
+                new[] { descriptor },
+                new DirectiveBlock(
+                    new DirectiveChunkGenerator(descriptor),
+                    Factory.CodeTransition(),
+                    Factory.MetaCode("custom").Accepts(AcceptedCharacters.None),
+                    Factory.Span(SpanKind.Markup, " ", markup: false).Accepts(AcceptedCharacters.WhiteSpace)));
+        }
+
         internal virtual void ParseCodeBlockTest(
             string document,
             IEnumerable<DirectiveDescriptor> descriptors,