Add test demonstrating the issue

Author: khellang

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/OperationTests.Controllers.cs

@@ -124,7 +124,7 @@ public class TestController : ControllerBase
 {
     /// <param name="userId">The id of the user.</param>
     [HttpGet("{userId}")]
-    public string Get()
+    public string Get(int userId)
     {
         return "Hello, World!";
     }
@@ -141,4 +141,49 @@ await SnapshotTestHelper.VerifyOpenApi(compilation, document =>
             Assert.Equal("The id of the user.", path.Parameters[0].Description);
         });
     }
+
+    [Fact]
+    public async Task SupportsRouteParametersWithCustomNamesFromControllers()
+    {
+        var source = """
+                     using Microsoft.AspNetCore.Builder;
+                     using Microsoft.AspNetCore.Mvc;
+                     using Microsoft.Extensions.DependencyInjection;
+
+                     var builder = WebApplication.CreateBuilder();
+
+                     builder.Services
+                         .AddControllers()
+                         .AddApplicationPart(typeof(TestController).Assembly);
+                     builder.Services.AddOpenApi();
+
+                     var app = builder.Build();
+
+                     app.MapControllers();
+
+                     app.Run();
+
+                     [ApiController]
+                     [Route("[controller]")]
+                     public class TestController : ControllerBase
+                     {
+                         /// <param name="userId">The id of the user.</param>
+                         [HttpGet("{user_id}")]
+                         public string Get([FromRoute(Name = "user_id")] int userId)
+                         {
+                             return "Hello, World!";
+                         }
+                     }
+
+                     public partial class Program {}
+
+                     """;
+        var generator = new XmlCommentGenerator();
+        await SnapshotTestHelper.Verify(source, generator, out var compilation);
+        await SnapshotTestHelper.VerifyOpenApi(compilation, document =>
+        {
+            var path = document.Paths["/Test/{user_id}"].Operations[HttpMethod.Get];
+            Assert.Equal("The id of the user.", path.Parameters[0].Description);
+        });
+    }
 }

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsRouteParametersFromControllers#OpenApiXmlCommentSupport.generated.verified.cs

@@ -71,7 +71,7 @@ private static Dictionary<string, XmlComment> GenerateCacheEntries()
         {
             var cache = new Dictionary<string, XmlComment>();
 
-            cache.Add(@"M:TestController.Get", new XmlComment(null, null, null, null, null, false, null, [new XmlParameterComment(@"userId", @"The id of the user.", null, false)], null));
+            cache.Add(@"M:TestController.Get(System.Int32)", new XmlComment(null, null, null, null, null, false, null, [new XmlParameterComment(@"userId", @"The id of the user.", null, false)], null));
 
             return cache;
         }