[CMake] Why is obj.dir/depend.make.tmp not renamed to obj.dir/depend.make?

[Steffen Dettmer]

Hi,

One (of really many) build trees contains a file "depend.make.tmp" and
ignores dependencies leading to broken (incremental) builds. There
also is a "depend.make" file in the same directory saying "Empty
dependencies file. This may be replaced when dependencies are built.",
so I assume the tmp file should be rename to it. The timestamp of the
tmp file is newer. I like to understand the cause and how to solve it.
I did not find any makefile rule that should do the rename.

The problem became visible in form of a SIGSEGV of a test application.
Analysing this down to the "depend.make.tmp" issue took quite a bit of
time, so I like to understand the root cause and learn how to avoid
it. Since only one build tree seems to be affected it seems to be a
very rare issue, maybe a race condition or such.

Any suggestions how I could analyse further?

Steffen