Merge the ctest2 repository into libc

[tgross35]

libc's testing is pretty tightly coupled to ctest2, which is a reasonably simple crate that maps Rust syntax to C syntax and creates tests based off of that. ctest2 itself is a fork of ctest.

Unfortunately, relying on ctest(2) has been somewhat of a problem since it supports only a very outdated version of Rust's syntax, and there are a handful of other bugs. There have been some GSoC proposals to modernize libc and its test crates; moving ctest to a rust-lang repo makes that easier and should come with some maintenance benefits.

On Zulip, @alexcrichton confirmed ownership of the original ctest crate could be transferred to rust-lang so we can continue publishing under that name, for other repos that make use of ctest/ctest2.

This pull only brings over the repo source and history as it currently exists. I will need to follow up with integration of the CI and release workflows.

[rustbot]

@tgross35: no appropriate reviewer found, use r? to override

[tgross35]

@JohnTitor would you be okay with libc absorbing ctest2, or do you have any concerns? You can continue to maintain it here if you wish of course.

[tgross35]

Also, does anyone know of a better way to merge unrelated histories? The blame works fine but the log appears empty.

[alexcrichton]

I think I've done something like this in the past using git filter-branch which rewrites the history as-if it all happened in a subfolder which should help with log/blame by ensuring the filenames don't change abruptly

[tgross35]

r? @JohnTitor

I of course don't want to poach your fork without your okay, so I'll assign you :) if you're fine going forward, I'll get the history better integrated as Alex suggested before merging.

[JohnTitor]

Yeah, no objection. Thank you!

[JohnTitor]

Some crates use ctest2 in their tests, so maybe I should add a deprecation notice and encourage to migrate in the ctest2 once the ctest supports the modern Rust.

[tgross35]

Github closed this on me when I pushed some unrelated history and won't let me reopen. Recreated as #4361

[tgross35]

Merged! 🎉 https://github.com/rust-lang/libc/tree/d5278fd7a746572c0c0b31d4a3d74366fbf5243e/ctest. Thanks Alex and Yuki for the help here.

I think I've done something like this in the past using git filter-branch which rewrites the history as-if it all happened in a subfolder which should help with log/blame by ensuring the filenames don't change abruptly

I wound up using git filter-repo (external tool recommended by git) rather than git filter-branch which worked out quite nice because it also rewrites shas mentioned in commit messages (e.g. reverts) and has a nice UI. The resulting history and blame look correct.

For future reference since I'm sure I'll need to do this again at some point:

# This was done on a fresh clone from ctest2

# Move to a subdirectory
git filter-repo --to-subdirectory-filter ctest

# Prefix all tags with `ctest-`
git filter-repo --tag-rename ':ctest-'

# The default merge messages are "merge pull request #nnn from user/branch"
# GH links these incorrectly in the new repo, so rename from `#nnn` to
# `JohnTitor/ctest2#nnn` (doesn't work for anything from the original `ctest`
# repo, but close enough).
echo 'regex:(^|\s)(#\d+)==>\1JohnTitor/ctest2\2' > messages.txt
git filter-repo --replace-message messages.txt

# After configuring a new remote (mine), push everything
git push --force --tags --prune tg-ctest2

# Now in the `libc` directory...

# Add that remote, fetch to update, etc
git remote add origin tg-ctest2 ...

# Merge, put something reasonable in the message
git merge tg-ctest2/... --allow-unrelated-histories

# Add whatever fixup commits are needed so CI passes,
# then push to `main` or use a PR.

# Tags didn't come through, so I just pushed them directly to rust-lang/libc
git push upstream tag 'ctest-*'