bug#26471: Automake 1.15 generates a recheck target that depends on all, breaking parallel builds

[Seth Fowler]

Hi folks,

I recently ran into what appears to be a bug in automake and I thought it would 
be a good idea to let you know.

We had noticed that running “make recheck -j8” if some source files were dirty 
would cause random build failures. The symptom was that the same file was 
getting built more than once by different make processes, which led to the 
resulting objects being corrupted. We’d see messages like this:

    libtool:   error: ‘foo.lo’ is not a valid libtool object

I dug into this a little and the root cause of the problem seems to be that 
unlike the other top-level targets generated by automake (check, install, 
etc.), recheck depends on “all” instead of “all-am”. “all” doesn’t declare very 
many dependencies - it just launches a new copy of make that builds “all-am”. 
Because recheck also depends on other targets (e.g. everything in 
check_PROGRAMS) which might depend on some of the same things as “all-am”, in a 
parallel build the original make process and the make process spawned by “all” 
can end up attempting to build the same targets.

I fixed this for our project by copying the generated recheck rule into our 
Makefile.am and replacing “all” with “all-am”. After doing this, I could no 
longer reproduce the problem with “make recheck -j8”.

It seems like that change should be made in automake itself. Or maybe I just 
missed something - I’m far from an automake guru. =)

Thanks,
- Seth