rustdoc: Tracking issue for command-line flag `--test-builder`

[ojeda]

FIXME: Write a proper synopsis.

Original description

The flag was added in the second commit of #64328, but I couldn't find a tracking issue (like #87022 for --no-run).

Is it meant to be stabilized?

• If yes: please feel free to reuse this as the tracking issue like in the --no-run one.
• If not: we are currently using it (together with --no-run) in the kernel to extract the source code of the tests, i.e. to achieve something similar to --persist-doctests, but for source code; or like --scrape-examples, but for doctests. Would there be a better/stable way to do that?

In the PR above [@]Mark-Simulacrum mentions:

This is largely intended for "advanced" users at this point (I'm not sure if we'll ever stabilize it)

[@]GuillaumeGomez

Note

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.

A tracking issue is however not meant for large scale discussion, questions, or bug reports.
Instead, open a dedicated issue for the specific matter or post in the #t-rustdoc Zulip channel.

Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Implementation PR
• Stabilization PR

Implementation history

• rustdoc: change doctests locating rustc binary #64328

[GuillaumeGomez]

I don't think it was intended for being stabilized.

[Mark-Simulacrum]

That PR tried to make it unstable (see the call to unstable in lib.rs), so we should track down the gap or PR that stabilized it.

[aDotInTheVoid]

Relevent zulip discussion on rust-for-linux's use of this to enable running doctests in kernelspace.