fix: honor OpenAPI transformer registration order

[baywet]

Fixes the OpenAPI transformer ordering issue discussed in https://github.com/dotnet/aspnetcore/issues/65723#issuecomment-5025789850.\n\nThis keeps the existing per-transformer-type lists while tracking registrations in a unified internal list so document transformers registered before operation/schema transformers can run before operation generation. This allows document transformers to pre-populate document-level tag metadata without operation tag discovery replacing it.\n\nValidation:\n- Docker: dotnet test src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Microsoft.AspNetCore.OpenApi.Tests.csproj --filter 'FullyQualifiedNameDocumentTransformerTests|FullyQualifiedNameOperationTransformerTests'

fixes #65723
closes #67457

[dotnet-policy-service]

Thanks for your PR, @baywet. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Youssef1313]

@halter73 Seems like it was very intentional, but I'm fine trying to change it and get feedback. I think we will still want to not do it in 11 as we are late in the release cycle right?

[Youssef1313]

This was introduced in #56395 by @martincostello

[Copilot]

Pull request overview

This PR updates OpenAPI document generation to honor the registration order of document/operation/schema transformers, enabling document transformers registered early to run before operation/path generation (e.g., to pre-populate tag metadata without later discovery overwriting it).

Changes:

• Track all transformer registrations in a unified internal list (OpenApiOptions.Transformers) while preserving the existing per-type lists.
• Update OpenApiDocumentService to generate paths at the first non-document transformer registration, allowing earlier document transformers to run pre-generation.
• Adjust/add tests to validate ordering behavior and the new unified registration list.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/OpenApi/src/Services/OpenApiOptions.cs	Adds unified Transformers registration list and appends registrations from each Add*Transformer overload.
src/OpenApi/src/Services/OpenApiDocumentService.cs	Applies unified ordering by interleaving document-transformer execution with a “generate paths once” boundary.
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Transformers/OpenApiOptionsTests.cs	Asserts transformers are also registered into the unified Transformers list.
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Transformers/OperationTransformerTests.cs	Updates ordering test to reflect the new semantics (document transformers run where registered).
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Transformers/DocumentTransformerTests.cs	Adds coverage for pre-generation document transformer behavior and ordering relative to operation transformers.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Transformers/DocumentTransformerTests.cs:7

• using Microsoft.AspNetCore.Http; is unused in this test file (all HttpMethod references come from System.Net.Http). With warnings treated as errors, this can break the build; please remove the unused using.

using Microsoft.AspNetCore.Http;

[dotnet-policy-service]

Looks like this PR hasn't been active for some time and the codebase could have been changed in the meantime.
To make sure no conflicting changes have occurred, please rerun validation before merging. You can do this by leaving an /azp run comment here (requires commit rights), or by simply closing and reopening.