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Date: Sat, 8 Mar 2025 00:10:50 -0500
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Subject: mv error building LilyPond tests, maybe MAX_PATH related
To: cygwin@cygwin.com
From: Saul Tobin via Cygwin <cygwin@cygwin.com>
Reply-To: Saul Tobin <saul.james.tobin@gmail.com>
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Hello,

I've encountered a kind of bizarre error when trying to build GNU LilyPond
regression tests on Cygwin 3.5.7-1 on Windows 11. For one and only one
folder, `mv` fails with `mv: cannot move './out-test' to
'./out-test-baseline': Permission denied`. The distinguishing feature of
the failing folder seems to be that it contains its own subfolder with a
copy of all the regtest files, some of which have rather long names. When I
remove this subfolder, the error goes away. The error also goes away if I
execute the rename in a way that forces a physical move of the files.

Based on this, it appears to me that when an in-place rename is performed
by `mv`, it calls into a Win32 API that enforces the 260 character
MAX_PATH. I can see in the trace that the error is occurring within a Win32
call stack for resolving absolute path names, though the error code isn't
specific enough to distinguish the precise reason for the failure.

I tried enabling LongPathsEnabled in the registry, but I get the same `mv`
error after doing so and rebooting.

I reported this as a LilyPond bug with some further detail here
https://gitlab.com/lilypond/lilypond/-/issues/6799, but the initial
sentiment seems to be that this is an upstream issue.

In some respect this doesn't seem like a specifically Cygwin issue, since I
encountered the same error in the same spot on WSL2 if the build tree was
on the Windows filesystem. But I'm guessing if anybody knows how to answer
this, it's probably folks on this list.

Any ideas what's going on here and how I might get it working? Is this a
known type of issue? Is it a bug? If it's a bug, what is it a bug in?

Right now, LilyPond's developer documentation basically just says not to
bother trying to compile on Windows. It would be REALLY nice to change
that, and this is the only blocking issue from recommending Cygwin as a
viable compilation environment for LilyPond development.

Thanks in advance for your help,

Saul

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