Fix exception sorting operation tags

src/Shared/OpenApiTagComparer.cs

@@ -0,0 +1,124 @@
+/*
+ * Copyright (c) Microsoft Corporation. All rights reserved.
+
+ * MIT License
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED *AS IS*, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ * 
+ */
+
+// Adapted from https://github.com/microsoft/OpenAPI.NET/blob/3b61b45991dded1aaecb16330430628d26a406de/src/Microsoft.OpenApi/OpenApiTagComparer.cs#L1
+
+namespace Microsoft.OpenApi;
+
+/// <summary>
+/// This comparer is used to maintain a globally unique list of tags encountered
+/// in a particular OpenAPI document.
+/// </summary>
+internal sealed class OpenApiTagComparer :
+    IComparer<IOpenApiTag>,
+    IComparer<OpenApiTagReference>,
+    IEqualityComparer<IOpenApiTag>,
+    IEqualityComparer<OpenApiTagReference>
+{
+    private static readonly Lazy<OpenApiTagComparer> _lazyInstance = new(() => new OpenApiTagComparer());
+
+    // Tag comparisons are case-sensitive by default. Although the OpenAPI specification
+    // only outlines case sensitivity for property names, we extend this principle to
+    // property values for tag names as well.
+    // See https://spec.openapis.org/oas/v3.1.0#format.
+    private static readonly StringComparer StringComparer = StringComparer.Ordinal;
+
+    /// <summary>
+    /// Default instance for the comparer.
+    /// </summary>
+    internal static OpenApiTagComparer Instance => _lazyInstance.Value;
+
+    public int Compare(IOpenApiTag x, IOpenApiTag y)
+    {
+        if (x is null)
+        {
+            return -1;
+        }
+
+        if (y is null)
+        {
+            return 1;
+        }
+
+        if (ReferenceEquals(x, y))
+        {
+            return 0;
+        }
+
+        if (x is OpenApiTagReference referenceX && y is OpenApiTagReference referenceY)
+        {
+            return StringComparer.Compare(referenceX.Name ?? referenceX.Reference.Id, referenceY.Name ?? referenceY.Reference.Id);
+        }
+
+        return StringComparer.Compare(x.Name, y.Name);
+    }
+
+    public int Compare(OpenApiTagReference x, OpenApiTagReference y)
+    {
+        if (x is null)
+        {
+            return -1;
+        }
+
+        if (y is null)
+        {
+            return 1;
+        }
+
+        if (ReferenceEquals(x, y))
+        {
+            return 0;
+        }
+
+        return StringComparer.Compare(x.Name ?? x.Reference.Id, y.Name ?? y.Reference.Id);
+    }
+
+    /// <inheritdoc/>
+    public bool Equals(IOpenApiTag x, IOpenApiTag y) => Compare(x, y) == 0;
+
+    /// <inheritdoc/>
+    public bool Equals(OpenApiTagReference x, OpenApiTagReference y) => Compare(x, y) == 0;
+
+    /// <inheritdoc/>
+    public int GetHashCode(IOpenApiTag obj)
+    {
+        string value = obj?.Name;
+
+        if (value is null && obj is OpenApiTagReference reference)
+        {
+            value = reference.Reference.Id;
+        }
+
+        return string.IsNullOrEmpty(value) ? 0 : StringComparer.GetHashCode(value);
+    }
+
+    /// <inheritdoc/>
+    public int GetHashCode(OpenApiTagReference obj)
+    {
+        string value = obj?.Name ?? obj?.Reference?.Id;
+
+        return string.IsNullOrEmpty(value) ? 0 : StringComparer.GetHashCode(value);
+    }
+}

src/Swashbuckle.AspNetCore.Annotations/AnnotationsDocumentFilter.cs

@@ -8,7 +8,7 @@ public class AnnotationsDocumentFilter : IDocumentFilter
 {
     public void Apply(OpenApiDocument swaggerDoc, DocumentFilterContext context)
     {
-        swaggerDoc.Tags ??= new SortedSet<OpenApiTag>();
+        swaggerDoc.Tags ??= new SortedSet<OpenApiTag>(OpenApiTagComparer.Instance);
 
         // Collect (unique) controller names and custom attributes in a dictionary
         var controllerNamesAndAttributes = context.ApiDescriptions

src/Swashbuckle.AspNetCore.Annotations/AnnotationsOperationFilter.cs

@@ -69,7 +69,7 @@ private static void ApplySwaggerOperationAttribute(
 
         if (swaggerOperationAttribute.Tags is { } tags)
         {
-            operation.Tags = new SortedSet<OpenApiTagReference>(tags.Select(tagName => new OpenApiTagReference(tagName)));
+            operation.Tags = new SortedSet<OpenApiTagReference>(tags.Select(tagName => new OpenApiTagReference(tagName)), OpenApiTagComparer.Instance);
         }
     }
 

src/Swashbuckle.AspNetCore.Annotations/Swashbuckle.AspNetCore.Annotations.csproj

@@ -24,5 +24,9 @@
     <AdditionalFiles Include="PublicAPI\$(TargetFramework)\PublicAPI.Shipped.txt" />
     <AdditionalFiles Include="PublicAPI\$(TargetFramework)\PublicAPI.Unshipped.txt" />
   </ItemGroup>
+
+  <ItemGroup>
+    <Compile Include="..\Shared\OpenApiTagComparer.cs" Link="OpenApiTagComparer.cs" />
+  </ItemGroup>
 
 </Project>

test/Swashbuckle.AspNetCore.Annotations.Test/AnnotationsOperationFilterTests.cs

@@ -28,7 +28,7 @@ public void Apply_EnrichesOperationMetadata_IfActionDecoratedWithSwaggerOperatio
         Assert.Equal("Summary for ActionWithSwaggerOperationAttribute", operation.Summary);
         Assert.Equal("Description for ActionWithSwaggerOperationAttribute", operation.Description);
         Assert.Equal("actionWithSwaggerOperationAttribute", operation.OperationId);
-        Assert.Equal(["foobar"], [.. operation.Tags.Select(t => t.Reference.Id)]);
+        Assert.Equal(["bar", "foo"], [.. operation.Tags.Select(t => t.Reference.Id)]);
     }
 
     [Fact]

test/Swashbuckle.AspNetCore.Annotations.Test/Fixtures/FakeControllerWithSwaggerAnnotations.cs

@@ -10,7 +10,7 @@ internal class FakeControllerWithSwaggerAnnotations
     [SwaggerOperation("Summary for ActionWithSwaggerOperationAttribute",
         Description = "Description for ActionWithSwaggerOperationAttribute",
         OperationId = "actionWithSwaggerOperationAttribute",
-        Tags = new[] { "foobar" }
+        Tags = ["foo", "bar"]
     )]
     public void ActionWithSwaggerOperationAttribute()
     { }