make checkstyle requires GNU parallel, but ./configure checks for any implementation

[Fabian-Gruenbichler]

System information

Debian/Ubuntu, but also applies to other distros where parallel is not (always) the GNU variant.

Describe the problem you're observing

config/always-parallel.m4 only checks for some parallel in $PATH, but the usage later requires that it supports -X0.

also see openzfs/openzfs-docs#489

Describe how to reproduce the problem

On a Debian/Ubuntu system don't install GNU parallel but only the version from moreutils, or set the system up to prefer that variant using alternatives.

Now run make checkstyle.

Include any warning/errors/backtraces from the system logs

parallel: invalid option -- 'X'
parallel [OPTIONS] command -- arguments
        for each argument, run command with argument, in parallel
parallel [OPTIONS] -- commands
        run specified commands in parallel
make: *** [Makefile:14243: cstyle] Error 1

How to fix

something like echo -e 'echo a\0echo b' | parallel -X0 can probably be used as test to determine whether the found parallel is good enough, but I lack the autotools knowledge to encode this in config/always_parallel.m4.

[ole-tange]

The officially supported way to check would be:

parallel --minversion 20220222 || echo parallel is older than 20220222

where 20220222 is the minimal version required.

Also have a look at --embed.

[Fabian-Gruenbichler]

that might be needed as well to catch old versions of GNU parallel, but I am talking about a different parallel from a different package. Debian and Ubuntu have a way to let two packages ship implementations of a certain binary in $PATH, managing which version is used by admin preference.

e.g., there is a /usr/bin/parallel in package moreutils, and one in package parallel. they both do the same job, but they don't have 100% identical parameters. in particular, the moreutils variant doesn't have -X. it also doesn't have --minversion ;)

this is also used for things like which variant of vi provides vi ;)

[ole-tange]

I am aware that you are testing to see if it is a different parallel command.

But that is the clever part: If the installed version is GNU Parallel and too old, it will fail. If it is moreutils' parallel, it will also fail (but for different reasons).

So by using --minversion you are both testing that the installed parallel is GNU and has a usable version. This will work until moreutils' parallel adopts --minversion (which I would reckon is unlikely to happen).