Fix OpenAPI generator crash on routes starting with '~'

[Copilot]

Fix OpenAPI generator crash on routes starting with '~'

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Store RoutePattern on ApiDescription to avoid reparsing

Description

MapRelativePathToItemPath was reparsing RelativePath with RoutePatternFactory.Parse(), which fails for routes starting with ~ since the stored path lacks the leading / (e.g., ~health vs /~health).

Solution: Add RoutePattern property to ApiDescription and populate it in both providers:

• EndpointMetadataApiDescriptionProvider uses routeEndpoint.RoutePattern
• DefaultApiDescriptionProvider parses from AttributeRouteInfo.Template
• MapRelativePathToItemPath uses stored pattern, falls back to parsing for compatibility

Example:

builder.MapGet("/~health", () => Results.Ok("Healthy"));
builder.MapOpenApi(); // Previously crashed, now works

Changes:

• Added RoutePattern property to ApiDescription
• Updated both API description providers to set the property
• Modified MapRelativePathToItemPath to use pre-parsed pattern
• Added routing assembly reference to Mvc.Abstractions
• Updated PublicAPI files

Tests:

• Added 3 unit tests verifying routes starting with ~
• Added integration test for minimal API endpoints with ~ routes
• Added integration test for MVC controller actions with ~ routes

Fixes #60967

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Microsoft.AspNetCore.OpenApi: The route template cannot start with a '~' character</issue_title>
<issue_description>### Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

The OpenApi generator crashes on routes that starts with a '~' character.

e.g.

app.MapGet("/~health", () => Results.Ok("Works"));

While the endpoint "/~health" works as expected, the openapi endpoint crashes

Expected Behavior

The OpenApi impl should also be compatible with routes that start with ~ (like aspnetcore does).

The ~ may not be pretty from a design approach but the behavior of the OpenApi generator should match the behavior of aspnetcore.

Offtopic:
We are currently considering to migrate from /~endpoint to /.endpoint because we ship internally some default endpoints on every app

Steps To Reproduce

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenApi();

var app = builder.Build();

app.MapGet("/", () => "Hello World!");

app.MapGet("/~health", () => Results.Ok("Works"));

app.MapOpenApi();

app.Run();

Exceptions (if any)

Microsoft.AspNetCore.Routing.Patterns.RoutePatternException: The route template cannot start with a '~' character unless followed by a '/'.
   at Microsoft.AspNetCore.Routing.Patterns.RoutePatternParser.TrimPrefix(String routePattern)
   at Microsoft.AspNetCore.Routing.Patterns.RoutePatternParser.Parse(String pattern)
   at ApiDescriptionExtensions.MapRelativePathToItemPath(ApiDescription apiDescription)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.<>c.<GetOpenApiPathsAsync>b__20_1(ApiDescription apiDescription)
   at System.Linq.Lookup`2.Create(IEnumerable`1 source, Func`2 keySelector, IEqualityComparer`1 comparer)
   at System.Linq.Enumerable.GroupByIterator`2.MoveNext()
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiPathsAsync(OpenApiDocument document, IServiceProvider scopedServiceProvider, IOpenApiOperationTransformer[] operationTransformers, IOpenApiSchemaTransformer[] schemaTransformers, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiDocumentAsync(IServiceProvider scopedServiceProvider, HttpRequest httpRequest, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Builder.OpenApiEndpointRouteBuilderExtensions.<>c__DisplayClass0_0.<<MapOpenApi>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>F0399B8B15BE443123F4BECEE84B112C1912EE3F44D9DDD7BFA38E371FB917343__GeneratedRouteBuilderExtensionsCore.<>c__DisplayClass2_0.<<MapGet0>g__RequestHandler|5>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

.NET Version

10.0.100

Anything else?

This issue only appears if the route starts with ~

e.g.

app.MapGet("/x~health", () => Results.Ok("Works"));

would work</issue_description>

<agent_instructions>Add a RoutePattern field to the ApiDescription type.

Set the field to the correct value in EndpointMetadataApiDescriptionProvider and DefaultApiDescriptionProvider.

Update ApiDescriptionExtensions.MapRelativePathToItemPath to use this new value.

Add tests to Microsoft.AspNetCore.OpenApi.Tests to validate the behavior when the /~health route is used on an endpoint.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@captainsafia @dp-sgr Great bug report! The fact that we pass the relative path to the RoutePatternParser is giving us grieve here.

The best way to address this is probably for us to store the RoutePattern somewhere on the ApiDescription so that we don't have to recreate it here. That'll probably require some tweaks to the shared framework but might be goodness all up.</comment_new>

• Fixes Microsoft.AspNetCore.OpenApi: The route template cannot start with a '~' character #64395

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[captainsafia]

@copilot Add a test that validates the behavior of these types of paths from a controller action.

[Copilot]

Added test GetOpenApiPaths_HandlesRoutesStartingWithTilde_MvcAction that validates routes starting with ~ from MVC controller actions. The test uses a controller action with [Route("/~health")] attribute and verifies the OpenAPI document is generated correctly. Commit: e48e103