Strip insignificant whitespace at compile time (#23385)

* Define @preservewhitespace directive attribute

* Have ComponentWhitespacePass respect preservewhitespace option

* Tests for overriding the preservewhitespace option (and fix implementation)

* Begin adding test infrastucture for ComponentWhitespacePass

* Remove leading/trailing whitespace from markup elements recursively

* Update baselines

* Add test showing we don't remove whitespace between sibling elements

* Remove whitespace before/after C# code statements (not expressions)

* Update baselines

* Slight improvements to test

* Remove leading/trailing whitespace inside component child content

* Update baselines

* Fix Razor tests

* Fix MVC test

* Better fix for MVC test

* CR: Make ComponentPreserveWhitespaceDirective conditional on langversion >= 5.0

src/Mvc/test/WebSites/BasicWebSite/RazorComponents/FetchData.razor

@@ -1,6 +1,6 @@
 @using BasicWebSite.Services
 @inject WeatherForecastService ForecastService
-
+@preservewhitespace true
 <h1>Weather forecast</h1>
 
 <p>This component demonstrates fetching data from the server.</p>
@@ -34,7 +34,6 @@ else
         </tbody>
     </table>
 }
-
 @code {
     [Parameter] public DateTime StartDate { get; set; }
 

src/Razor/Microsoft.AspNetCore.Mvc.Razor.Extensions/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/BasicComponent_Runtime.codegen.cs

@@ -34,7 +34,6 @@ protected override void BuildRenderTree(Microsoft.AspNetCore.Components.Renderin
 #line hidden
 #nullable disable
             );
-            __builder.AddMarkupContent(4, "\r\n");
             __builder.CloseElement();
         }
         #pragma warning restore 1998

src/Razor/Microsoft.AspNetCore.Mvc.Razor.Extensions/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/BasicComponent_Runtime.ir.txt

@@ -16,7 +16,5 @@ Document -
                         LazyIntermediateToken - (74:3,0 [4] BasicComponent.cshtml) - Html -     
                     CSharpExpression - (79:3,5 [29] BasicComponent.cshtml)
                         LazyIntermediateToken - (79:3,5 [29] BasicComponent.cshtml) - CSharp - string.Format("{0}", "Hello")
-                    HtmlContent - (108:3,34 [2] BasicComponent.cshtml)
-                        LazyIntermediateToken - (108:3,34 [2] BasicComponent.cshtml) - Html - \n
             CSharpCode - (132:6,12 [37] BasicComponent.cshtml)
                 LazyIntermediateToken - (132:6,12 [37] BasicComponent.cshtml) - CSharp - \n    void IDisposable.Dispose(){ }\n

src/Razor/Microsoft.AspNetCore.Razor.Language/src/ComponentResources.resx

@@ -201,6 +201,15 @@
   <data name="PageDirective_RouteToken_Name" xml:space="preserve">
     <value>route template</value>
   </data>
+  <data name="PreserveWhitespaceDirective_BooleanToken_Description" xml:space="preserve">
+    <value>True if whitespace should be preserved, otherwise false.</value>
+  </data>
+  <data name="PreserveWhitespaceDirective_BooleanToken_Name" xml:space="preserve">
+    <value>Preserve</value>
+  </data>
+  <data name="PreserveWhitespaceDirective_Description" xml:space="preserve">
+    <value>Specifies whether or not whitespace should be preserved exactly. Defaults to false for better performance.</value>
+  </data>
   <data name="RefTagHelper_Documentation" xml:space="preserve">
     <value>Populates the specified field or property with a reference to the element or component.</value>
   </data>

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentPreserveWhitespaceDirective.cs

@@ -0,0 +1,30 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Razor.Language.Components
+{
+    internal static class ComponentPreserveWhitespaceDirective
+    {
+        public static readonly DirectiveDescriptor Directive = DirectiveDescriptor.CreateDirective(
+            "preservewhitespace",
+            DirectiveKind.SingleLine,
+            builder =>
+            {
+                builder.AddBooleanToken(ComponentResources.PreserveWhitespaceDirective_BooleanToken_Name, ComponentResources.PreserveWhitespaceDirective_BooleanToken_Description);
+                builder.Usage = DirectiveUsage.FileScopedMultipleOccurring;
+                builder.Description = ComponentResources.PreserveWhitespaceDirective_Description;
+            });
+
+        public static void Register(RazorProjectEngineBuilder builder)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            builder.AddDirective(Directive, FileKinds.Component, FileKinds.ComponentImport);
+        }
+    }
+}

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentWhitespacePass.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
 using Microsoft.AspNetCore.Razor.Language.Intermediate;
 
 namespace Microsoft.AspNetCore.Razor.Language.Components
@@ -38,17 +39,45 @@ protected override void ExecuteCore(RazorCodeDocument codeDocument, DocumentInte
                 return;
             }
 
+            // Respect @preservewhitespace directives
+            if (PreserveWhitespaceIsEnabled(documentNode))
+            {
+                return;
+            }
+
             var method = documentNode.FindPrimaryMethod();
             if (method != null)
             {
                 RemoveContiguousWhitespace(method.Children, TraversalDirection.Forwards);
                 RemoveContiguousWhitespace(method.Children, TraversalDirection.Backwards);
+
+                var visitor = new Visitor();
+                visitor.Visit(method);
+            }
+        }
+
+        private static bool PreserveWhitespaceIsEnabled(DocumentIntermediateNode documentNode)
+        {
+            // If there's no @preservewhitespace attribute, the default is that we *don't* preserve whitespace
+            var shouldPreserveWhitespace = false;
+
+            foreach (var preserveWhitespaceDirective in documentNode.FindDirectiveReferences(ComponentPreserveWhitespaceDirective.Directive))
+            {
+                var token = ((DirectiveIntermediateNode)preserveWhitespaceDirective.Node).Tokens.FirstOrDefault();
+                var shouldPreserveWhitespaceContent = token?.Content;
+                if (shouldPreserveWhitespaceContent != null)
+                {
+                    shouldPreserveWhitespace = string.Equals(shouldPreserveWhitespaceContent, "true", StringComparison.Ordinal);
+                }
             }
+
+            return shouldPreserveWhitespace;
         }
 
-        private static void RemoveContiguousWhitespace(IntermediateNodeCollection nodes, TraversalDirection direction)
+        private static int RemoveContiguousWhitespace(IntermediateNodeCollection nodes, TraversalDirection direction, int? startIndex = null)
         {
-            var position = direction == TraversalDirection.Forwards ? 0 : nodes.Count - 1;
+            var position = startIndex.GetValueOrDefault(direction == TraversalDirection.Forwards ? 0 : nodes.Count - 1);
+            var countRemoved = 0;
             while (position >= 0 && position < nodes.Count)
             {
                 var node = nodes[position];
@@ -76,7 +105,7 @@ private static void RemoveContiguousWhitespace(IntermediateNodeCollection nodes,
                         shouldContinueIteration = false;
                         break;
 
-                    case CSharpCodeIntermediateNode codeIntermediateNode:
+                    case CSharpCodeIntermediateNode _:
                         shouldRemoveNode = false;
                         shouldContinueIteration = false;
                         break;
@@ -90,6 +119,7 @@ private static void RemoveContiguousWhitespace(IntermediateNodeCollection nodes,
                 if (shouldRemoveNode)
                 {
                     nodes.RemoveAt(position);
+                    countRemoved++;
                     if (direction == TraversalDirection.Forwards)
                     {
                         position--;
@@ -103,12 +133,48 @@ private static void RemoveContiguousWhitespace(IntermediateNodeCollection nodes,
                     break;
                 }
             }
+
+            return countRemoved;
         }
 
         enum TraversalDirection
         {
             Forwards,
             Backwards
         }
+
+        class Visitor : IntermediateNodeWalker
+        {
+            public override void VisitMarkupElement(MarkupElementIntermediateNode node)
+            {
+                RemoveContiguousWhitespace(node.Children, TraversalDirection.Forwards);
+                RemoveContiguousWhitespace(node.Children, TraversalDirection.Backwards);
+                VisitDefault(node);
+            }
+
+            public override void VisitTagHelperBody(TagHelperBodyIntermediateNode node)
+            {
+                // The goal here is to remove leading/trailing whitespace inside component child content. However,
+                // at the time this whitespace pass runs, ComponentChildContent is still TagHelperBody in the tree.
+                RemoveContiguousWhitespace(node.Children, TraversalDirection.Forwards);
+                RemoveContiguousWhitespace(node.Children, TraversalDirection.Backwards);
+                VisitDefault(node);
+            }
+
+            public override void VisitDefault(IntermediateNode node)
+            {
+                // For any CSharpCodeIntermediateNode children, remove their preceding and trailing whitespace
+                for (var childIndex = 0; childIndex < node.Children.Count; childIndex++)
+                {
+                    if (node.Children[childIndex] is CSharpCodeIntermediateNode)
+                    {
+                        childIndex -= RemoveContiguousWhitespace(node.Children, TraversalDirection.Backwards, childIndex - 1);
+                        RemoveContiguousWhitespace(node.Children, TraversalDirection.Forwards, childIndex + 1);
+                    }
+                }
+
+                base.VisitDefault(node);
+            }
+        }
     }
 }

src/Razor/Microsoft.AspNetCore.Razor.Language/src/DirectiveDescriptorBuilderExtensions.cs

@@ -117,6 +117,28 @@ public static IDirectiveDescriptorBuilder AddAttributeToken(this IDirectiveDescr
             return builder;
         }
 
+        public static IDirectiveDescriptorBuilder AddBooleanToken(this IDirectiveDescriptorBuilder builder)
+        {
+            return AddBooleanToken(builder, name: null, description: null);
+        }
+
+        public static IDirectiveDescriptorBuilder AddBooleanToken(this IDirectiveDescriptorBuilder builder, string name, string description)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            builder.Tokens.Add(
+                DirectiveTokenDescriptor.CreateToken(
+                    DirectiveTokenKind.Boolean,
+                    optional: false,
+                    name: name,
+                    description: description));
+
+            return builder;
+        }
+
         public static IDirectiveDescriptorBuilder AddOptionalMemberToken(this IDirectiveDescriptorBuilder builder)
         {
             return AddOptionalMemberToken(builder, name: null, description: null);

src/Razor/Microsoft.AspNetCore.Razor.Language/src/DirectiveTokenKind.cs

@@ -10,5 +10,6 @@ public enum DirectiveTokenKind
         Member,
         String,
         Attribute,
+        Boolean,
     }
 }

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

@@ -1322,7 +1322,8 @@ private void ParseExtensibleDirective(in SyntaxListBuilder<RazorSyntaxNode> buil
                             if (tokenDescriptor.Kind == DirectiveTokenKind.Member ||
                                 tokenDescriptor.Kind == DirectiveTokenKind.Namespace ||
                                 tokenDescriptor.Kind == DirectiveTokenKind.Type ||
-                                tokenDescriptor.Kind == DirectiveTokenKind.Attribute)
+                                tokenDescriptor.Kind == DirectiveTokenKind.Attribute ||
+                                tokenDescriptor.Kind == DirectiveTokenKind.Boolean)
                             {
                                 SpanContext.ChunkGenerator = SpanChunkGenerator.Null;
                                 SpanContext.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.Whitespace;
@@ -1417,6 +1418,22 @@ private void ParseExtensibleDirective(in SyntaxListBuilder<RazorSyntaxNode> buil
                                     return;
                                 }
                                 break;
+
+                            case DirectiveTokenKind.Boolean:
+                                if (AtBooleanLiteral() && !CurrentToken.ContainsDiagnostics)
+                                {
+                                    AcceptAndMoveNext();
+                                }
+                                else
+                                {
+                                    Context.ErrorSink.OnError(
+                                        RazorDiagnosticFactory.CreateParsing_DirectiveExpectsBooleanLiteral(
+                                            new SourceSpan(CurrentStart, CurrentToken.Content.Length), descriptor.Directive));
+                                    builder.Add(BuildDirective());
+                                    return;
+                                }
+                                break;
+
                             case DirectiveTokenKind.Attribute:
                                 if (At(SyntaxKind.LeftBracket))
                                 {
@@ -1699,6 +1716,12 @@ private bool TryParseKeyword(in SyntaxListBuilder<RazorSyntaxNode> builder, IRea
             return false;
         }
 
+        private bool AtBooleanLiteral()
+        {
+            var result = CSharpTokenizer.GetTokenKeyword(CurrentToken);
+            return result.HasValue && (result.Value == CSharpKeyword.True || result.Value == CSharpKeyword.False);
+        }
+
         private void SetupExpressionParsers()
         {
             MapExpressionKeyword(ParseAwaitExpression, CSharpKeyword.Await);

src/Razor/Microsoft.AspNetCore.Razor.Language/src/RazorDiagnosticFactory.cs

@@ -426,6 +426,16 @@ public static RazorDiagnostic CreateParsing_DirectiveExpectsCSharpAttribute(Sour
         {
             return RazorDiagnostic.Create(Parsing_DirectiveExpectsCSharpAttribute, location, directiveName);
         }
+
+        internal static readonly RazorDiagnosticDescriptor Parsing_DirectiveExpectsBooleanLiteral =
+            new RazorDiagnosticDescriptor(
+                $"{DiagnosticPrefix}1038",
+                () => Resources.DirectiveExpectsBooleanLiteral,
+                RazorDiagnosticSeverity.Error);
+        public static RazorDiagnostic CreateParsing_DirectiveExpectsBooleanLiteral(SourceSpan location, string directiveName)
+        {
+            return RazorDiagnostic.Create(Parsing_DirectiveExpectsBooleanLiteral, location, directiveName);
+        }
         #endregion
 
         #region Semantic Errors

src/Razor/Microsoft.AspNetCore.Razor.Language/src/RazorProjectEngine.cs

@@ -120,7 +120,7 @@ public static RazorProjectEngine Create(
                 NamespaceDirective.Register(builder);
                 AttributeDirective.Register(builder);
 
-                AddComponentFeatures(builder);
+                AddComponentFeatures(builder, configuration.LanguageVersion);
             }
 
             LoadExtensions(builder, configuration.Extensions);
@@ -206,7 +206,7 @@ private static void AddDefaultFeatures(ICollection<IRazorFeature> features)
             });
         }
 
-        private static void AddComponentFeatures(RazorProjectEngineBuilder builder)
+        private static void AddComponentFeatures(RazorProjectEngineBuilder builder, RazorLanguageVersion razorLanguageVersion)
         {
             // Project Engine Features
             builder.Features.Add(new ComponentImportProjectFeature());
@@ -218,6 +218,11 @@ private static void AddComponentFeatures(RazorProjectEngineBuilder builder)
             ComponentPageDirective.Register(builder);
             ComponentTypeParamDirective.Register(builder);
 
+            if (razorLanguageVersion.CompareTo(RazorLanguageVersion.Version_5_0) >= 0)
+            {
+                ComponentPreserveWhitespaceDirective.Register(builder);
+            }
+
             // Document Classifier
             builder.Features.Add(new ComponentDocumentClassifierPass());
 

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

@@ -559,4 +559,7 @@
   <data name="TagHelper_InvalidRequiredDirectiveAttributeName" xml:space="preserve">
     <value>Invalid tag helper required directive attribute '{0}'. The directive attribute '{1}' should start with a '@' character.</value>
   </data>
+  <data name="DirectiveExpectsBooleanLiteral" xml:space="preserve">
+    <value>The '{0}' directive expects a boolean literal.</value>
+  </data>
 </root>

src/Razor/Microsoft.AspNetCore.Razor.Language/test/Components/ComponentMarkupBlockPassTest.cs

@@ -47,11 +47,9 @@ public void Execute_RewritesHtml_Basic()
 </html>");
 
             var expected = NormalizeContent(@"
-<html>
-  <head cool=""beans"">
+<html><head cool=""beans"">
     Hello, World!
-  </head>
-</html>");
+  </head></html>");
 
             var documentNode = Lower(document);
 
@@ -163,7 +161,7 @@ public void Execute_RewritesHtml_CSharpInAttributes()
   </head>
 </html>");
 
-            var expected = NormalizeContent("<div>foo</div>\n  ");
+            var expected = NormalizeContent("<div>foo</div>");
 
             var documentNode = Lower(document);
 
@@ -349,11 +347,8 @@ public void Execute_CanRewriteHtml_OptionWithNoSelectAncestor()
 </html>");
 
             var expected = NormalizeContent(@"
-<head cool=""beans"">
-    <option value=""1"">One</option>
-    <option selected value=""2"">Two</option>
-  </head>
-");
+<head cool=""beans""><option value=""1"">One</option>
+    <option selected value=""2"">Two</option></head>");
 
             var documentNode = Lower(document);