Bug#677874: lintian: checks/manpages is unreasonably slow on some packages

[Niels Thykier <niels@thykier.net>]

Package: lintian
Version: 2.5.9
Severity: normal

Hi,

I noticed [1] and decided to check what made Lintian a "lengthy
invariant".  Processing the changes (and related files) took about a
minute (accoriding to the shell built-in time).  Running:

 $ time lintian -d -C manpages allegro4-doc_4.4.2-2_all.deb

takes about 40 seconds.

The bottleneck appears to our calls to "man" in checks/manpages.
Manually running man on all the manpages takes roughly 30 seconds.  As
far as I can tell, man is "just slow" (at least with currently
selected options).

Running man in a collection is unlikely to yield any noticable
improvement[2].  Even with xargs we are looking at at least 25 seconds
plus man is unhelpful in this case[3].

~Niels

[1] https://lists.debian.org/debian-release/2012/06/msg00446.html

[2] It will still take 30 seconds and the total time we spend in other
collections do not even compare to that.

[3] It emits errors when running with xargs that do not occur when
running them in serial.  The error messages all use "<standard input>"
rather than a filename, so it will be... difficult to relate them to
the original manpage.