Abort sl root call if output resembles a steam locomotive

[rmartine-ias]

Summary

Jest detects whether a repository is a sapling repo by calling the sl
binary, and getting the output. If sl (steam locomotive) is installed,
the output of sl root 1) takes forever to get and 2) is not the root,
but a moving image of a steam locomotive. This change monitors the
stdout stream, and aborts the sl call if the first character is an
escape character, which indicates that the terminal is being cleared to
make way for a train to come through.

See also: #14046

Test plan

This was tested manually. I don't think I have the time to figure out
automated testing for this, as it requires installing a binary, which
means mucking around in the CI code.

With the existing main branch, with sl on $PATH:

$ node ~/dev/jest/packages/jest/bin/jest.js --watch
Determining test suites to run...

  ● Test suite failed to run

thrown: [Error]

With the existing main branch, in a repo with sapling roots, with sapling on $PATH:

$ node ~/dev/jest/packages/jest/bin/jest.js --watch

<a bunch of output>

With the proposed changes, with sl on $PATH:

$ node ~/dev/jest/packages/jest/bin/jest.js --watch
No tests found related to files changed since last commit.

With the proposed changes, in a repo with sapling roots, with sapling on $PATH:

$ node ~/dev/jest/packages/jest/bin/jest.js --watch

<a bunch of output>

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[vegerot]

Choo-choo-choose to celebrate! 🎊 This bug has been a runaway train 🚆, derailing devs for years since I laid down the tracks for this feature. 🛤️ Let's conduct a thorough inspection 🕵️‍♂️ and write a test to ensure this patch stays on the right track 🛤️ and doesn't cause any more train wrecks. 💥🚈

[SimenB]

this is awesome!

Should we set some module scoped variable so we can reuse in findChangedFiles (and also skip the spawn)?

(in addition, please add a changelog entry 🙂 )

[rmartine-ias]

Added changelog entry.

Should we set some module scoped variable so we can reuse in findChangedFiles (and also skip the spawn)?

Do you mean like this @SimenB? Not sure what we'd be re-using in sl.findChangedFiles, since I don't think it gets called if we don't find any roots. This new change means we spawn at most 5 sl processes. I could move the logic into index.ts and delay calling sl.getRoot until we know what type of sl is installed, if that's what you mean?

[SimenB]

Should we set some module scoped variable so we can reuse in findChangedFiles (and also skip the spawn)?

Do you mean like this @SimenB?

That, yes 🙂

---

Not sure what we'd be re-using in sl.findChangedFiles, since I don't think it gets called if we don't find any roots.

Right, that makes sense

[SimenB]

thank you! This has long been a pain point, hopefully this is good enough 🙂

[SimenB]

https://github.com/jestjs/jest/releases/tag/v30.0.0-alpha.4

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