Add new Use middleware extension method

[BrennanConroy]

Description

Add a new app.Use overload that requires users to pass the HttpContext to the next function which will save 2 per-request allocations over the previous extension method.

Customer Impact

Less per-request allocations when using simple middleware.

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

[Justify the selection above]
Terminal middleware that used app.Use will need to update to use app.Run otherwise they'll get an ambiguous method compile error. We'd like to get this in early to get feedback on how bad that is, or if it isn't a problem.

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

Fixes #31463

---

Main change is located at https://github.com/dotnet/aspnetcore/compare/brecon/use?expand=1#diff-e80bc3e234b6da05aea986e2aaa5b92bf492f085e00e7497d268e107169c9c6c
and
https://github.com/dotnet/aspnetcore/compare/brecon/use?expand=1#diff-dcc7a146ff62319dc1f9ab1847a9697596a4d899e7f75b588ed3c74d594ea305

The rest is changing all our tests and samples to use the new overload, or switch to app.Run if they never called next.

Should we file a breaking change announcement that people calling app.Use without calling next will be broken?

Note: We should apply this same change to the ConnectionBuilder

aspnetcore/src/Servers/Connections.Abstractions/src/ConnectionBuilderExtensions.cs

Line 42 in 686da2e

Func<Task> simpleNext = () => next(context);

TODO: File docs issue to update code to use new overload

[davidfowl]

Is this a breaking change?

[pranavkm]

Could you also add a quip about preferring Run if next is unused?

[BrennanConroy]

Done

[Tratcher]

I'm curious to get this into a preview and see if we get any feedback about it. People will only notice it on re-compile, and I wonder how obvious it will be if they need to switch to Run.

[davidfowl]

This should be in for preview4 if we're going to do it.

[ghost]

Hello human! Please make sure you've included the Shiproom Template in a comment or (preferably) the PR description. Also, make sure this PR is not marked as a draft and is ready-to-merge.

[halter73]

I like it, and I think we should do this for preview4. I'm not sure the risk is "low" though. This breaking change broke a couple samples and a lot of tests that were using Use instead of Run for terminal middleware, right? I don't think it's that uncommon of a pattern.

This is at least "medium" risk, right?

[BrennanConroy]

I see risk as more of "possibility of breaking your applications behavior unexpectedly". This wont break your apps behavior, you might just need to modify your code slightly to compile.

[halter73]

So compile-time breaking changes that don't change runtime behavior of apps that still compile without changes are considered "low" risk? And the number existing apps that work in .NET 5 and won't compile after this change has absolutely no impact on the risk?

I guess I can get behind that for previews since we can always revert and there's a simple code fix. I'm just surprised that's the standard.

[BrennanConroy]

I mean, that's my opinion, not a standard. And risk in this case doesn't mean the same thing as it does for patches and RC releases. If we were making a compile time breaking change in a patch, then this would be Extremely high risk.

But like you noted, since this is a preview and we can revert it later, low risk.

[halter73]

Should we file a breaking change announcement that people calling app.Use without calling next will be broken?

Yes. What does the compile error look like exactly BTW?

[BrennanConroy]

CS0121 The call is ambiguous between the following methods or properties: 'UseExtensions.Use(IApplicationBuilder, Func<HttpContext, Func, Task>)' and 'UseExtensions.Use(IApplicationBuilder, Func<HttpContext, RequestDelegate, Task>)'

[BrennanConroy]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[BrennanConroy]

@dotnet/aspnet-build
Feel free to merge whenever

[Rick-Anderson]

TODO: File docs issue to update code to use new overload

dotnet/AspNetCore.Docs#23688

[ghost]

Hi @Rick-Anderson. It looks like you just commented on a closed PR. The team will most probably miss it. If you'd like to bring something important up to their attention, consider filing a new issue and add enough details to build context.