Use Minimal APIs JSON options when MVC is not registered

[RaphaelFakhri]

Fixes #3097.

IOptions<Microsoft.AspNetCore.Mvc.JsonOptions> resolves in any application, whether or not MVC was ever registered, so the existing fallback to IOptions<Microsoft.AspNetCore.Http.Json.JsonOptions> never ran: in a Minimal APIs application the MVC defaults were returned and the options set through ConfigureHttpJsonOptions were ignored. The generated document then contradicted what the endpoints actually serialize, which is the case in the report: the endpoint returns {"HelloWorld":"hi"} while the schema documents helloWorld.

The MVC options are now preferred only when MVC is actually registered, detected through IControllerFactory. I checked that it is registered by AddControllers(), AddMvcCore() and AddMvc(), and by nothing a Minimal APIs application uses, including AddEndpointsApiExplorer(), which is why IActionDescriptorCollectionProvider is not the marker here.

When an application registers both, MVC keeps precedence exactly as before: one document is generated with one set of serializer options, so a tie-break is unavoidable and this is the one that does not change existing behaviour. An application that configures neither is unaffected, since both option types default to the same web defaults.

Four tests in SwaggerGenServiceCollectionExtensionsTests: Minimal APIs only, MVC only, both registered, and neither configured. Swashbuckle.AspNetCore.SwaggerGen.Test passes on net8.0, net9.0 and net10.0 with 764 tests, 0 failed.

It turns out the repo's own Minimal APIs sample already demonstrates the bug: test/WebSites/WebApi adds a JsonStringEnumConverter through Microsoft.AspNetCore.Http.Json.JsonOptions and never registers MVC, but the committed snapshots document DateTimeKind as an int32 enum (0, 1, 2) while the endpoints actually serialize "Unspecified", "Utc" and "Local". With this change the generated document matches what the sample really returns, and the six snapshots are updated accordingly; every changed hunk is that one schema.

This deliberately takes the no-new-public-API route rather than reviving what #3378 attempted, since that PR was closed with an invitation to start fresh.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.24%. Comparing base (d0b1e26) to head (fdd4aa1).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4116   +/-   ##
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  Coverage   95.24%   95.24%           
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  Files         111      111           
  Lines        4142     4143    +1     
  Branches      848      848           
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+ Hits         3945     3946    +1     
  Misses        197      197           

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Linux	95.24% <100.00%> (+<0.01%)	⬆️
Windows	95.24% <100.00%> (+<0.01%)	⬆️
macOS	95.24% <100.00%> (+<0.01%)	⬆️

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[RaphaelFakhri]

The branch is rebased onto current master and the change is now limited to SwaggerGenServiceCollectionExtensions and its test class.

One set of snapshots still changes, and it is a direct result of the fix rather than a wider code change. The WebApi sample registers JsonStringEnumConverter through Configure<JsonOptions> (Minimal APIs) and does not register MVC. Before this change, Swashbuckle read MVC's default options and ignored that registration, so the DateTimeKind enum was documented as integers even though the application serializes it as strings. The VerifyTests snapshots for WebApi (net8.0, net9.0, net10.0) and the Kiota and NSwag client snapshots generated from them now show the string values. The last commit contains only those regenerated files.

If you prefer that the sample stays unchanged, the alternative is to add AddControllers() to the sample, which keeps the old output but no longer exercises the Minimal APIs path.

[github-actions]

Thanks for your contribution @RaphaelFakhri - the changes from this pull request have been published as part of version 10.3.0 📦, which is now available from NuGet.org 🚀