Subject: Re: [PATCH v11] setup: improve error diagnosis for invalid .git files

From: Tian Yuchen <[email-masked]>
Date: Sat, 28 Feb 2026 12:38:54 +0800

Hi Junio,

Thanks for pushing back on my previous suggestion.

> It sounds like saying "oh, this is too hard, let's punt and roll all
> failures from stat() into 'nothing there, move on'", which is how
> the code used to work before this patch X-<.

Yeah, that's why I said this idea was pretty dumb. XD

Regarding your question about how 'stat()' gets into the picture, I 
tried GDB debugging and simulated Windows behavior by 'GIT_DIR=nul' (I'm 
NOT sure if it's correct). Here is the back trace caught:

(gdb) print path
$1 = 0x555555a86dd0 "nul"
(gdb) bt
#0  read_gitfile_gently (path=0x555555a86dd0 "nul", return_error_code=0x0)
     at setup.c:936
#1  0x000055555589dea1 in setup_explicit_git_dir (
     gitdirenv=0x555555a86dd0 "nul", cwd=0x555555a58070 <cwd>,
     repo_fmt=0x7fffffffcbe0, nongit_ok=0x7fffffffccc4) at setup.c:1107
#2  0x000055555589fd53 in setup_git_directory_gently 
(nongit_ok=0x7fffffffccc4)
     at setup.c:1867
#3  0x00005555555c1383 in cmd_diff (argc=4, argv=0x555555a86ce0, 
prefix=0x0,
     repo=0x0) at builtin/diff.c:458
#4  0x0000555555575e30 in run_builtin (p=0x555555a48368 <commands+840>,
     argc=4, argv=0x555555a86ce0, repo=0x555555a7bdc0 <the_repo>) at 
git.c:506
#5  0x0000555555576354 in handle_builtin (args=0x7fffffffdc10) at git.c:780
#6  0x000055555557667e in run_argv (args=0x7fffffffdc10) at git.c:863
#7  0x0000555555576b44 in cmd_main (argc=4, argv=0x7fffffffdda0) at 
git.c:985
#8  0x00005555556a73bf in main (argc=5, argv=0x7fffffffdd98) at 
common-main.c:9

Sorry it might be a bit messy. It turns out that 
'setup_explicit_git_dir()' calls 'read_gitfile_gently()' right away to 
check whether GIT_DIR is actually a gitfile, right?

Since stat("nul") fails on windows, STAT_FAILED was caught and 
immediately triggered die(), blowing up corresponding CI tests.

Still, I don't know Windows well. These thoughts are just to stimulate 
discussions. （　´_ゝ`）

Thanks,

Yuchen