Add CI check to ensure that rustdoc JSON FORMAT_VERSION is correctly updated

[GuillaumeGomez]

Follow-up of #142601.

Tested it locally with: BASE_COMMIT=1bb335244c311a07cee165c28c553c869e6f64a9 src/ci/docker/host-x86_64/mingw-check-1/validate-rustdoc-json-format-version-update.sh (where BASE_COMMIT value was the commit before I made a wrong change with the FORMAT_VERSION update).

This is a first version. I plan to send a follow-up to also ensure that FORMAT_VERSION is updated if any code change is done in rustdoc-json-types. For that I just need to check that a line not starting with / and not an empty line was updated. Fun times with grep ahead. :')

cc @aDotInTheVoid
r? @nnethercote

[rustbot]

nnethercote is not on the review rotation at the moment.
They may take a while to respond.

[Kobzol]

Could this be a tidy check instead? It's better to have these things in one centralized place in Rust, rather than scattered around in random bash scripts.

[GuillaumeGomez]

I guess? Didn't even realize that I could do the same in rust much more easily. ^^'

[GuillaumeGomez]

Moved it to tidy. I'll do the same with the other bash tidy check I added.

[GuillaumeGomez]

Oh also:

r? @Kobzol

[Kobzol]

I guess it could also work locally, but it's always a PITA to figure out a diff vs master, so this is fine. Could you please try to break the CI job in this PR to see if it works on PR CI?

[rustbot]

rustdoc-json-types is a public (although nightly-only) API. If possible, consider changing src/librustdoc/json/conversions.rs; otherwise, make sure you bump the FORMAT_VERSION constant.

cc @CraftSpider, @aDotInTheVoid, @Enselic, @obi1kenobi

[Kobzol]

2025-06-19T11:27:57.5354234Z [TIMING] core::build_steps::tool::Tidy { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu } -- 0.000
2025-06-19T11:27:57.5354975Z fmt check
2025-06-19T11:28:04.5397272Z fmt: checked 6074 files
2025-06-19T11:28:05.0397217Z tidy check
2025-06-19T11:28:24.2535092Z Running eslint on rustdoc JS files
2025-06-19T11:28:29.4054908Z tidy: Skipping binary file check, read-only filesystem
2025-06-19T11:28:36.0337263Z removing old virtual environment
2025-06-19T11:28:36.0359346Z creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'venv'
2025-06-19T11:28:36.0843019Z creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'virtualenv'
2025-06-19T11:28:37.6050421Z Requirement already satisfied: pip in ./build/venv/lib/python3.10/site-packages (25.1.1)
2025-06-19T11:28:38.8879878Z linting python files
2025-06-19T11:28:39.0477863Z All checks passed!
2025-06-19T11:28:39.0488259Z checking python file formatting
2025-06-19T11:28:39.1812151Z 28 files already formatted
2025-06-19T11:28:39.1822499Z checking C++ file formatting
2025-06-19T11:28:41.0313008Z x.py completions check

Looks like the check didn't run, hmm. Probably adding some logging before the return; statements would be useful, to figure out why. And also printing the output of git diff.

[GuillaumeGomez]

It's because BASE_COMMIT is not set in tidy. Changing that.