Add warning wave support and warn for unnecessary @ in component parameters

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Components/ComponentLoweringPass.cs

@@ -12,9 +12,16 @@ namespace Microsoft.AspNetCore.Razor.Language.Components;
 
 internal class ComponentLoweringPass : ComponentIntermediateNodePassBase, IRazorOptimizationPass
 {
+    private readonly int? _razorWarningLevel;
+
     // This pass runs earlier than our other passes that 'lower' specific kinds of attributes.
     public override int Order => 0;
 
+    public ComponentLoweringPass(RazorConfiguration configuration)
+    {
+        _razorWarningLevel = configuration.RazorWarningLevel;
+    }
+
     protected override void ExecuteCore(RazorCodeDocument codeDocument, DocumentIntermediateNode documentNode)
     {
         if (!IsComponentDocument(documentNode))
@@ -137,7 +144,7 @@ static TagHelperDescriptor GetTagHelperOrAddDiagnostic(TagHelperIntermediateNode
         }
     }
 
-    private static ComponentIntermediateNode RewriteAsComponent(TagHelperIntermediateNode node, TagHelperDescriptor tagHelper)
+    private ComponentIntermediateNode RewriteAsComponent(TagHelperIntermediateNode node, TagHelperDescriptor tagHelper)
     {
         var component = new ComponentIntermediateNode()
         {
@@ -163,6 +170,7 @@ private static ComponentIntermediateNode RewriteAsComponent(TagHelperIntermediat
         }
 
         ValidateRequiredAttributes(node, tagHelper, component);
+        WarnForUnnecessaryAt(component);
 
         return component;
     }
@@ -213,6 +221,27 @@ static bool IsPresentAsAttribute(string attributeName, ComponentIntermediateNode
         }
     }
 
+    private void WarnForUnnecessaryAt(ComponentIntermediateNode component)
+    {
+        if (_razorWarningLevel is not >= 9)
+        {
+            return;
+        }
+
+        foreach (var attribute in component.Attributes)
+        {
+            // IntParam="@x" has unnecessary `@`, can just use IntParam="x" -> warn
+            // StrParam="@x" is different than StrParam="x" -> don't warn
+            if (!attribute.BoundAttribute.IsStringProperty &&
+                attribute.Source is { } originalSource &&
+                attribute.Children is [CSharpExpressionIntermediateNode])
+            {
+                var source = originalSource.With(length: 1, endCharacterIndex: originalSource.CharacterIndex + 1);
+                attribute.Diagnostics.Add(RazorDiagnosticFactory.CreateComponentParameter_UnnecessaryAt(source));
+            }
+        }
+    }
+
     private static MarkupElementIntermediateNode RewriteAsElement(TagHelperIntermediateNode node)
     {
         var result = new MarkupElementIntermediateNode()

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/RazorConfiguration.cs

@@ -12,7 +12,8 @@ public sealed record class RazorConfiguration(
     string ConfigurationName,
     ImmutableArray<RazorExtension> Extensions,
     LanguageServerFlags? LanguageServerFlags = null,
-    bool UseConsolidatedMvcViews = false)
+    bool UseConsolidatedMvcViews = false,
+    int? RazorWarningLevel = null)
 {
     public static readonly RazorConfiguration Default = new(
         RazorLanguageVersion.Latest,
@@ -27,6 +28,7 @@ public bool Equals(RazorConfiguration? other)
            ConfigurationName == other.ConfigurationName &&
            LanguageServerFlags == other.LanguageServerFlags &&
            UseConsolidatedMvcViews == other.UseConsolidatedMvcViews &&
+           RazorWarningLevel == other.RazorWarningLevel &&
            Extensions.SequenceEqual(other.Extensions);
 
     public override int GetHashCode()
@@ -37,6 +39,7 @@ public override int GetHashCode()
         hash.Add(Extensions);
         hash.Add(UseConsolidatedMvcViews);
         hash.Add(LanguageServerFlags);
+        hash.Add(RazorWarningLevel);
         return hash;
     }
 }

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/RazorDiagnosticFactory.cs

@@ -480,6 +480,14 @@ public static RazorDiagnostic CreateTagHelper_InconsistentTagStructure(SourceSpa
     public static RazorDiagnostic CreateComponent_EditorRequiredParameterNotSpecified(SourceSpan? location, string tagName, string parameterName)
         => RazorDiagnostic.Create(Component_EditorRequiredParameterNotSpecified, location, tagName, parameterName);
 
+    internal static readonly RazorDiagnosticDescriptor ComponentParameter_UnnecessaryAt =
+        new($"{DiagnosticPrefix}2013",
+            Resources.ComponentParameter_UnnecessaryAt,
+            RazorDiagnosticSeverity.Warning);
+
+    public static RazorDiagnostic CreateComponentParameter_UnnecessaryAt(SourceSpan? location)
+        => RazorDiagnostic.Create(ComponentParameter_UnnecessaryAt, location);
+
     #endregion
 
     #region TagHelper Errors

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/RazorProjectEngine.cs

@@ -363,7 +363,7 @@ public static RazorProjectEngine Create(
             NamespaceDirective.Register(builder);
             AttributeDirective.Register(builder);
 
-            AddComponentFeatures(builder, configuration.LanguageVersion);
+            AddComponentFeatures(builder, configuration);
         }
 
         configure?.Invoke(builder);
@@ -448,8 +448,10 @@ private static void AddDefaultFeatures(ImmutableArray<IRazorFeature>.Builder fea
         });
     }
 
-    private static void AddComponentFeatures(RazorProjectEngineBuilder builder, RazorLanguageVersion razorLanguageVersion)
+    private static void AddComponentFeatures(RazorProjectEngineBuilder builder, RazorConfiguration configuration)
     {
+        RazorLanguageVersion razorLanguageVersion = configuration.LanguageVersion;
+
         // Project Engine Features
         builder.Features.Add(new ComponentImportProjectFeature());
 
@@ -486,7 +488,7 @@ private static void AddComponentFeatures(RazorProjectEngineBuilder builder, Razo
 
         // Optimization
         builder.Features.Add(new ComponentComplexAttributeContentPass());
-        builder.Features.Add(new ComponentLoweringPass());
+        builder.Features.Add(new ComponentLoweringPass(configuration));
         builder.Features.Add(new ComponentEventHandlerLoweringPass());
         builder.Features.Add(new ComponentKeyLoweringPass());
         builder.Features.Add(new ComponentReferenceCaptureLoweringPass());

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Resources.resx

@@ -574,6 +574,9 @@
   <data name="Component_EditorRequiredParameterNotSpecified" xml:space="preserve">
     <value>Component '{0}' expects a value for the parameter '{1}', but a value may not have been provided.</value>
   </data>
+  <data name="ComponentParameter_UnnecessaryAt" xml:space="preserve">
+    <value>The '@' prefix is not necessary for component parameters whose type is not string.</value>
+  </data>
   <data name="An_item_with_the_same_key_has_already_been_added_Key_0" xml:space="preserve">
     <value>An item with the same key has already been added. Key: {0}</value>
   </data>

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/Diagnostics/DiagnosticIds.cs

@@ -6,6 +6,7 @@ namespace Microsoft.NET.Sdk.Razor.SourceGenerators
     internal static class DiagnosticIds
     {
         public const string InvalidRazorLangVersionRuleId = "RZ3600";
+        public const string InvalidRazorWarningLevelRuleId = "RZ3601";
         public const string ReComputingTagHelpersRuleId = "RSG001";
         public const string TargetPathNotProvidedRuleId = "RSG002";
         public const string GeneratedOutputFullPathNotProvidedRuleId = "RSG003";

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/Diagnostics/RazorDiagnostics.cs

@@ -20,6 +20,14 @@ internal static class RazorDiagnostics
             DiagnosticSeverity.Error,
             isEnabledByDefault: true);
 
+        public static readonly DiagnosticDescriptor InvalidRazorWarningLevelDescriptor = new DiagnosticDescriptor(
+            DiagnosticIds.InvalidRazorWarningLevelRuleId,
+            new LocalizableResourceString(nameof(RazorSourceGeneratorResources.InvalidRazorWarningLevelTitle), RazorSourceGeneratorResources.ResourceManager, typeof(RazorSourceGeneratorResources)),
+            new LocalizableResourceString(nameof(RazorSourceGeneratorResources.InvalidRazorWarningLevelMessage), RazorSourceGeneratorResources.ResourceManager, typeof(RazorSourceGeneratorResources)),
+            "RazorSourceGenerator",
+            DiagnosticSeverity.Error,
+            isEnabledByDefault: true);
+
         public static readonly DiagnosticDescriptor ReComputingTagHelpersDescriptor = new DiagnosticDescriptor(
             DiagnosticIds.ReComputingTagHelpersRuleId,
             new LocalizableResourceString(nameof(RazorSourceGeneratorResources.RecomputingTagHelpersTitle), RazorSourceGeneratorResources.ResourceManager, typeof(RazorSourceGeneratorResources)),

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/Diagnostics/RazorSourceGeneratorResources.resx

@@ -121,7 +121,13 @@
     <value>Invalid RazorLangVersion</value>
   </data>
   <data name="InvalidRazorLangMessage" xml:space="preserve">
-    <value>Invalid value '{0}'' for RazorLangVersion. Valid values include 'Latest' or a valid version in range 1.0 to 8.0.</value>
+    <value>Invalid value '{0}' for RazorLangVersion. Valid values include 'Latest' or a valid version in range 1.0 to 8.0.</value>
+  </data>
+	<data name="InvalidRazorWarningLevelTitle" xml:space="preserve">
+    <value>Invalid RazorWarningLevel</value>
+  </data>
+	<data name="InvalidRazorWarningLevelMessage" xml:space="preserve">
+    <value>Invalid value '{0}' for RazorWarningLevel. Must be empty or an integer.</value>
   </data>
   <data name="RecomputingTagHelpersTitle" xml:space="preserve">
     <value>Recomputing tag helpers</value>

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/IncrementalValueProviderExtensions.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.AspNetCore.Razor;
 using Microsoft.CodeAnalysis;
@@ -39,12 +40,12 @@ internal static IncrementalValuesProvider<TSource> ReportDiagnostics<TSource>(th
             return source.Where((pair) => pair.Item1 != null).Select((pair, ct) => pair.Item1!);
         }
 
-        internal static IncrementalValueProvider<TSource> ReportDiagnostics<TSource>(this IncrementalValueProvider<(TSource?, Diagnostic?)> source, IncrementalGeneratorInitializationContext context)
+        internal static IncrementalValueProvider<TSource> ReportDiagnostics<TSource>(this IncrementalValueProvider<(TSource?, ImmutableArray<Diagnostic>)> source, IncrementalGeneratorInitializationContext context)
         {
             context.RegisterSourceOutput(source, (spc, source) =>
             {
-                var (_, diagnostic) = source;
-                if (diagnostic != null)
+                var (_, diagnostics) = source;
+                foreach (var diagnostic in diagnostics)
                 {
                     spc.ReportDiagnostic(diagnostic);
                 }

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/RazorSourceGenerator.RazorProviders.cs

@@ -2,10 +2,12 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Immutable;
 using System.IO;
 using System.Text;
 using System.Threading;
 using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Diagnostics;
@@ -14,7 +16,7 @@ namespace Microsoft.NET.Sdk.Razor.SourceGenerators
 {
     public partial class RazorSourceGenerator
     {
-        private (RazorSourceGenerationOptions?, Diagnostic?) ComputeRazorSourceGeneratorOptions(((AnalyzerConfigOptionsProvider, ParseOptions), bool) pair, CancellationToken ct)
+        private (RazorSourceGenerationOptions?, ImmutableArray<Diagnostic>) ComputeRazorSourceGeneratorOptions(((AnalyzerConfigOptionsProvider, ParseOptions), bool) pair, CancellationToken ct)
         {
             var ((options, parseOptions), isSuppressed) = pair;
             var globalOptions = options.GlobalOptions;
@@ -31,18 +33,42 @@ public partial class RazorSourceGenerator
             globalOptions.TryGetValue("build_property.SupportLocalizedComponentNames", out var supportLocalizedComponentNames);
             globalOptions.TryGetValue("build_property.GenerateRazorMetadataSourceChecksumAttributes", out var generateMetadataSourceChecksumAttributes);
 
-            Diagnostic? diagnostic = null;
+            using var diagnostics = new PooledArrayBuilder<Diagnostic>();
             if (!globalOptions.TryGetValue("build_property.RazorLangVersion", out var razorLanguageVersionString) ||
                 !RazorLanguageVersion.TryParse(razorLanguageVersionString, out var razorLanguageVersion))
             {
-                diagnostic = Diagnostic.Create(
+                diagnostics.Add(Diagnostic.Create(
                     RazorDiagnostics.InvalidRazorLangVersionDescriptor,
                     Location.None,
-                    razorLanguageVersionString);
+                    razorLanguageVersionString));
                 razorLanguageVersion = RazorLanguageVersion.Latest;
             }
 
-            var razorConfiguration = new RazorConfiguration(razorLanguageVersion, configurationName ?? "default", Extensions: [], UseConsolidatedMvcViews: true);
+            globalOptions.TryGetValue("build_property.RazorWarningLevel", out var razorWarningLevelString);
+            int? razorWarningLevel;
+            if (string.IsNullOrEmpty(razorWarningLevelString))
+            {
+                razorWarningLevel = null;
+            }
+            else if (!int.TryParse(razorWarningLevelString, out var razorWarningLevelInt))
+            {
+                diagnostics.Add(Diagnostic.Create(
+                    RazorDiagnostics.InvalidRazorWarningLevelDescriptor,
+                    Location.None,
+                    razorWarningLevelString));
+                razorWarningLevel = null;
+            }
+            else
+            {
+                razorWarningLevel = razorWarningLevelInt;
+            }
+
+            var razorConfiguration = new RazorConfiguration(
+                razorLanguageVersion,
+                configurationName ?? "default",
+                Extensions: [],
+                UseConsolidatedMvcViews: true,
+                RazorWarningLevel: razorWarningLevel);
 
             var razorSourceGenerationOptions = new RazorSourceGenerationOptions()
             {
@@ -54,7 +80,7 @@ public partial class RazorSourceGenerator
                 TestSuppressUniqueIds = _testSuppressUniqueIds,
             };
 
-            return (razorSourceGenerationOptions, diagnostic);
+            return (razorSourceGenerationOptions, diagnostics.DrainToImmutable());
         }
 
         private static (SourceGeneratorProjectItem?, Diagnostic?) ComputeProjectItems((AdditionalText, AnalyzerConfigOptionsProvider) pair, CancellationToken ct)

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/RazorSourceGeneratorComponentTests.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
@@ -274,6 +275,79 @@ public static class RuntimeHelpers
         Assert.DoesNotContain("AddComponentParameter", source.SourceText.ToString());
     }
 
+    [Theory]
+    [InlineData(null, false)]
+    [InlineData("", false)]
+    [InlineData("8", false)]
+    [InlineData("9", true)]
+    [InlineData("10", true)]
+    [InlineData("999", true)]
+    public async Task ComponentParameter_UnnecessaryAt(string warningLevel, bool hasWarnings)
+    {
+        // Arrange
+        var project = CreateTestProject(new()
+        {
+            ["Views/Home/Index.cshtml"] = """
+                @(await Html.RenderComponentAsync<MyApp.Shared.Component1>(RenderMode.Static))
+                """,
+            ["Shared/Component1.razor"] = """
+                @{
+                    var hi = "str";
+                    var x = 21;
+                }
+                <Component2 IntParam="42" StrParam="hi" />
+                <Component2
+                    IntParam="@(43)"
+                    StrParam="@hi" />
+                <Component2
+                    IntParam="@x"
+                    StrParam="@("lit")" />
+                <Component2 IntParam="x * 3" StrParam="@(hi + "hey")" />
+                <Component2 IntParam=@x />
+                """,
+            ["Shared/Component2.razor"] = """
+                I: @(IntParam + 1), S: @StrParam?.ToUpperInvariant()
+
+                @code {
+                    [Parameter] public int IntParam { get; set; }
+                    [Parameter] public string? StrParam { get; set; }
+                }
+                """
+        });
+        var compilation = await project.GetCompilationAsync();
+        var driver = await GetDriverAsync(project, options =>
+        {
+            if (warningLevel != null)
+            {
+                options.TestGlobalOptions["build_property.RazorWarningLevel"] = warningLevel;
+            }
+        });
+
+        // Act
+        var result = RunGenerator(compilation!, ref driver, out compilation);
+
+        // Assert
+        if (hasWarnings)
+        {
+            result.Diagnostics.VerifyRazor(project,
+                // Shared/Component1.razor(7,15): warning RZ2013: The '@' prefix is not necessary for component parameters whose type is not string.
+                //     IntParam="@(43)"
+                Diagnostic("RZ2013", "@").WithLocation(7, 15),
+                // Shared/Component1.razor(10,15): warning RZ2013: The '@' prefix is not necessary for component parameters whose type is not string.
+                //     IntParam="@x"
+                Diagnostic("RZ2013", "@").WithLocation(10, 15),
+                // Shared/Component1.razor(13,22): warning RZ2013: The '@' prefix is not necessary for component parameters whose type is not string.
+                // <Component2 IntParam=@x />
+                Diagnostic("RZ2013", "@").WithLocation(13, 22));
+        }
+        else
+        {
+            result.Diagnostics.VerifyRazor(project);
+        }
+        Assert.Equal(3, result.GeneratedSources.Length);
+        await VerifyRazorPageMatchesBaselineAsync(compilation, "Views_Home_Index");
+    }
+
     [Fact, WorkItem("https://github.com/dotnet/razor/issues/8660")]
     public async Task TypeArgumentsCannotBeInferred()
     {