Tracking Issue for rustdoc --test-builder

[ojeda]

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

[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.