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Re: [PATCH] build: do not require help2man at build-from-tarball time

From: Jim Meyering
Subject: Re: [PATCH] build: do not require help2man at build-from-tarball time
Date: Mon, 10 Sep 2012 12:46:23 +0200

Stefano Lattarini wrote:
> Hi Jim.
> On 09/10/2012 09:41 AM, Jim Meyering wrote:
>> We can't have build-from-tarball requiring perl (via help2man)
>> or regenerating a distributed .1 file when its .c file has not changed.
>> From 57da212a95054cc230ffb00f38ea655c798926f8 Mon Sep 17 00:00:00 2001
>> From: Jim Meyering <address@hidden>
>> Date: Sun, 9 Sep 2012 19:27:25 +0200
>> Subject: [PATCH] build: do not require help2man at build-from-tarball time
>> But do retain full dependencies when building from a git clone.
>> We do this by converting the full dependency (of the .1 file on
>> the binary we run with --help) into a dependency on the .c file.
>> * (do-not-require-help2man): New rule.
>> (dist-hook): depend on it.
> I believe this is incorrect.  Think of what happens if a user building from
> the tarball modifies, say, 'src/ls.c', and then runs "make -j8" to rebuild
> everything: make will see that it has to rebuild the man page 'man/ls.1'
> (because its prerequisite 'src/ls.c' has changed), but won't see that it
> has to rebuild 'src/ls' before re-running 'help2man' ro generate that man
> page; so, if 'man/ls.1' is rebuilt before 'src/ls' (which can happen with
> concurrent make), our user will get either a build error (if 'src/ls' was
> non-existent) or, worse, a man page with an up-to-date timestamp but an
> out-of-date content.  And what's even worse is that this problem will be
> present also for users who have perl installed!
> So we are breaking correctness for all tarball users only to accommodate
> those few crippled systems lacking a decent perl.
> I think the right way to go is "graceful degradation": we should keep the
> correct dependency for man pages ("man/ls.1: src/ls"); and if perl is not
> present, we should use, instead of help2man, a shell script that just
> emit a "placeholder" man page stating that a real man page couldn't be
> built due to lack of perl, and redirecting the user back to either the
> info documentation or the '--help' output.

Hi Stefano,

Thanks for reviewing that.

I have mixed feelings.  If someone is modifying sources and expecting
to be able to rebuild, they'd better have developer tools like perl.

On the other hand, I dislike distributing a deliberately hamstrung, even though this wart is only in a generated file, that
could easily be regenerated without the reduced dependency -- again,
assuming proper tools.

An added bonus of your approach: we would no longer need to distribute
the man/*.1 files, and instead would generate them unconditionally, even
from tarballs.

Do you feel like writing the patch, and especially documenting what
would amount to a new, soft, build-from-tarball dependency on Perl?


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