build/bootstrap/.last-warned-change-id gets removed by workaround for #125578

[lolbinarycat]

bootstrap.py contains this snippet:

                # FIXME: A cheap workaround for https://github.com/rust-lang/rust/issues/125578,
                # remove this once the issue is closed.
                bootstrap_out = self.bootstrap_out()
                if os.path.exists(bootstrap_out):
                    shutil.rmtree(bootstrap_out)

                p.map(unpack_component, tarballs_download_info)

when updating to a new master, bootstrap gets rebuilt, causing the "last warned change id" file to be deleted, so you see all the "new changes to x.py", even if there are no new changes to x.py.

[lolbinarycat]

We are deleting .last-warned-change-id again.

We probably want to write a regression test this time.

[Kobzol]

I wonder if we should just write that file to the source root and add it to .gitignore.. 🤔

[Kobzol]

Could you post some reproduction of how was the file deleted for you?

[lolbinarycat]

@Kobzol just running ./x clean deletes it (but not .rustc_info.json, weirdly).

just tested and reproduced on bfc046a

here's the config:

profile = "tools"  # Includes one of the default files in src/bootstrap/defaults
change-id = 143300

rust.debuginfo-level = 1
#rust.jemalloc = true
rust.download-rustc = false
rust.deny-warnings = false
build.docs-minification = false
#build.incremental = false
build.tidy-extra-checks = "auto:py"

[Kobzol]

Looks like it's kind of expected?

rust/src/bootstrap/src/core/build_steps/clean.rs

Line 148 in cda9bfe

rm_rf(&build.out.join("bootstrap").join(".last-warned-change-id"));

[lolbinarycat]

strange, wonder why that is...

I mean, the change-id system isn't actually super reliable, because PRs aren't always merged in the order they are opened, but removing .last-warned-change-id doesn't really seem like the best answer to that.