https://github.com/rust-lang/rust is not bisectable

Hi. It seems that either "git bisect" has a bug, either repo at https://github.com/rust-lang/rust is broken.

(Keep in mind that Rust project has somehow custom git setup: https://doc.rust-lang.org/nightly/clippy/development/infrastructure/sync.html#patching-git-subtree-to-work-with-big-repos )

So, here are steps to reproduce. I use fresh debian sid with git 2.39.0.

root@f6ca188fd101:/# git clone https://github.com/rust-lang/rust Cloning into 'rust'... remote: Enumerating objects: 2107155, done. remote: Counting objects: 100% (145/145), done. remote: Compressing objects: 100% (79/79), done. remote: Total 2107155 (delta 73), reused 102 (delta 64), pack-reused 2107010 Receiving objects: 100% (2107155/2107155), 1009.95 MiB | 2.74 MiB/s, done. Resolving deltas: 100% (1647434/1647434), done. Updating files: 100% (38754/38754), done. root@f6ca188fd101:/# cd rust

Now let's notice that commit 7175c499ecc32cb3ff713be0bbac9fd12990a34e has word "bootstrap" in file "compiler/rustc_target/src/abi/mod.rs", but commit 49c2279ef658d8732597c4da93897d84838f3df5 (master as of 2022-12-17) - does not.

Also, let's notice that 7175c499ecc32cb3ff713be0bbac9fd12990a34e is an ancestor of 49c2279ef658d8732597c4da93897d84838f3df5. (Everywhere I say that X is an ancestor of Y, I mean that X can be found in "git log Y", in other words "git log Y | grep -q '^commit X' " returns true.)

Now let's find the first commit, which doesn't contain "bootstrap" in that file in this interval. Let's do it using "git bisect".

root@f6ca188fd101:/rust# git bisect start
status: waiting for both good and bad commits
root@f6ca188fd101:/rust# git bisect good
7175c499ecc32cb3ff713be0bbac9fd12990a34e
status: waiting for bad commit, 1 good commit known
root@f6ca188fd101:/rust# git bisect bad 49c2279ef658d8732597c4da93897d84838f3df5
Bisecting: 23901 revisions left to test after this (roughly 15 steps)
[26562973b3482a635416b2b663a13016d4d90e20] Auto merge of #13653 -
VannTen:fix/doc-typo-vim-lsp, r=Veykril

Okay, so "git bisect" gave us commit 26562973b3482a635416b2b663a13016d4d90e20. And here I see a bug: 7175c499ecc32cb3ff713be0bbac9fd12990a34e is NOT ancestor of 26562973b3482a635416b2b663a13016d4d90e20! But I think "git bisect" should give us some commit between "good" and "bad", so presumably "good" should be an ancestor of the commit returned by "git bisect".