[release/8.0] Fix route analyzer performance with highly concatenated strings

src/Framework/AspNetCoreAnalyzers/src/Analyzers/RouteEmbeddedLanguage/Infrastructure/RouteStringSyntaxDetector.cs

@@ -149,6 +149,19 @@ private static bool HasLanguageComment(
             return true;
         }
 
+        // Check for the common case of a string literal in a large binary expression.  For example `"..." + "..." +
+        // "..."` We never want to consider these as regex/json tokens as processing them would require knowing the
+        // contents of every string literal, and having our lexers/parsers somehow stitch them all together.  This is
+        // beyond what those systems support (and would only work for constant strings anyways).  This prevents both
+        // incorrect results *and* avoids heavy perf hits walking up large binary expressions (often while a caller is
+        // themselves walking down such a large expression).
+        if (token.Parent.IsLiteralExpression() &&
+            token.Parent.Parent.IsBinaryExpression() &&
+            token.Parent.Parent.RawKind == (int)SyntaxKind.AddExpression)
+        {
+            return false;
+        }
+
         for (var node = token.Parent; node != null; node = node.Parent)
         {
             if (HasLanguageComment(node.GetLeadingTrivia(), out identifier, out options))

src/Framework/AspNetCoreAnalyzers/src/Analyzers/RouteEmbeddedLanguage/Infrastructure/SyntaxNodeExtensions.cs

@@ -33,6 +33,12 @@ public static SyntaxNode GetRequiredParent(this SyntaxNode node)
         return parent;
     }
 
+    public static bool IsLiteralExpression([NotNullWhen(true)] this SyntaxNode? node)
+        => node is LiteralExpressionSyntax;
+
+    public static bool IsBinaryExpression([NotNullWhen(true)] this SyntaxNode? node)
+        => node is BinaryExpressionSyntax;
+
     [return: NotNullIfNotNull("node")]
     public static SyntaxNode? WalkUpParentheses(this SyntaxNode? node)
     {

src/Framework/AspNetCoreAnalyzers/test/Microsoft.AspNetCore.App.Analyzers.Test.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>$(DefaultNetCoreTargetFramework)</TargetFramework>

src/Framework/AspNetCoreAnalyzers/test/RouteEmbeddedLanguage/RoutePatternAnalyzerTests.cs

@@ -1,17 +1,28 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using System.Globalization;
+using System.Text;
 using Microsoft.AspNetCore.Analyzer.Testing;
 using Microsoft.AspNetCore.Analyzers.RenderTreeBuilder;
 using Microsoft.AspNetCore.Analyzers.RouteEmbeddedLanguage.Infrastructure;
+using Microsoft.CodeAnalysis;
+using Xunit.Abstractions;
 
 namespace Microsoft.AspNetCore.Analyzers.RouteEmbeddedLanguage;
 
 public partial class RoutePatternAnalyzerTests
 {
+    private readonly ITestOutputHelper _testOutputHelper;
+
     private TestDiagnosticAnalyzerRunner Runner { get; } = new(new RoutePatternAnalyzer());
 
+    public RoutePatternAnalyzerTests(ITestOutputHelper testOutputHelper)
+    {
+        _testOutputHelper = testOutputHelper;
+    }
+
     [Fact]
     public async Task CommentOnString_ReportResults()
     {
@@ -512,4 +523,125 @@ public object TestAction(int id)
         // Assert
         Assert.Empty(diagnostics);
     }
+
+    [Fact]
+    public async Task ConcatString_PerformanceTest()
+    {
+        // Arrange
+        var builder = new StringBuilder();
+        builder.AppendLine("""
+    class Program
+    {
+        static void Main() { }
+        static readonly string _s =
+    """);
+        for (var i = 0; i < 2000; i++)
+        {
+            builder.AppendLine("        \"a{}bc\" +");
+        }
+        builder.AppendLine("""
+            "";
+    }
+    """);
+        var source = TestSource.Read(builder.ToString());
+
+        // Act 1
+        // Warm up.
+        var diagnostics1 = await Runner.GetDiagnosticsAsync(source.Source);
+
+        // Assert 1
+        Assert.Empty(diagnostics1);
+
+        // Act 2
+        // Measure analysis.
+        var stopwatch = Stopwatch.StartNew();
+
+        var diagnostics2 = await Runner.GetDiagnosticsAsync(source.Source);
+        _testOutputHelper.WriteLine($"Elapsed time: {stopwatch.Elapsed}");
+
+        // Assert 2
+        Assert.Empty(diagnostics2);
+    }
+
+    [Fact]
+    public async Task ConcatString_DetectLanguage_NoWarningsBecauseConcatString()
+    {
+        // Arrange
+        var builder = new StringBuilder();
+        builder.AppendLine("""
+    class Program
+    {
+        static void Main() { }
+        // lang=Route
+        static readonly string _s =
+    """);
+        for (var i = 0; i < 2000; i++)
+        {
+            builder.AppendLine("        \"a{}bc\" +");
+        }
+        builder.AppendLine("""
+            "";
+    }
+    """);
+        var source = TestSource.Read(builder.ToString());
+
+        // Act
+        var diagnostics = await Runner.GetDiagnosticsAsync(source.Source);
+
+        // Assert
+        Assert.Empty(diagnostics);
+    }
+
+    [Fact]
+    public async Task NestedLangComment_NoWarningsBecauseConcatString()
+    {
+        // Arrange
+        var builder = new StringBuilder();
+        builder.AppendLine("""
+    class Program
+    {
+        static void Main() { }
+        static readonly string _s =
+            "{/*MM0*/te*st0}" +
+            // lang=Route
+            "{/*MM1*/te*st1}" +
+            "{/*MM2*/te*st2}" +
+            "{test3}";
+    }
+    """);
+        var source = TestSource.Read(builder.ToString());
+
+        // Act
+        var diagnostics = await Runner.GetDiagnosticsAsync(source.Source);
+
+        // Assert
+        Assert.Empty(diagnostics);
+    }
+
+    [Fact]
+    public async Task TopLangComment_NoWarningsBecauseConcatString()
+    {
+        // Arrange
+        var builder = new StringBuilder();
+        builder.AppendLine("""
+    class Program
+    {
+        static void Main() { }
+        static readonly string _s =
+            // lang=Route
+            "{/*MM0*/te*st0}" +
+            "{/*MM1*/te*st1}" +
+            "{/*MM2*/te*st2}" +
+            // lang=regex
+            "{test3}";
+    }
+    """);
+        var source = TestSource.Read(builder.ToString());
+
+        // Act
+        var diagnostics = await Runner.GetDiagnosticsAsync(source.Source);
+
+        // Assert
+        Assert.Empty(diagnostics);
+    }
 }