i've set up darcsweb using darcs 2.3.0 and the cgi module of lighttpd. when i
click on a commitdiff link then darcs is invoked so that it (or one of its
dependencies) calls getEnv (instead of getEnvironment) which throws an exception
if $PATH is not set. the error message is this:

darcs: PATH: getEnv: does not exist (no environment variable)

any words on this? thanks in advance!

Atilla: thanks for the report!  Is there any way could could convince darcsweb
to log the darcs commands it's executing?  What happens when you click on that
commitdiff link?

Darcs developers: when I grepped the darcs source looking for PATH, I got
nothing which indicates that darcs ever directly looks for this.

% grep -r PATH src 
src/best_practices.tex:It can cause surprises if you have a ``wrong'' darcs in
your PATH.
src/Darcs/Commands/Push.lhs:ssh login@remote.machine 'echo $PATH'
src/Darcs/Resolution.lhs:you should make sure the command is in your \verb!PATH!. 
src/Darcs/Utils.hs: "found in your PATH, emacs, emacs -nw, nano and (on Windows)
edit are",

i don't know what darcsweb issues, but it's very easy to reproduce this:

$ darcs --version
2.3.1 (release)
$ unset PATH
$ ~/bin/darcs diff
darcs: PATH: getEnv: does not exist (no environment variable)

fyi, i had to add "PATH=/usr/bin" for the environment when we invoke darcsweb
with our home-grown cgi engine.

i think this happens because darcs invokes the diff executable from the path,
which is a bit surprising... it should at least emit a useful error message
along the line of "hey, i need to exec diff and i cannot find it in the PATH!"

other than that, now everything works here.

Thanks to this follow-up I was able to do a tiny bit of digging through the
Darcs code, I can reproduce the problem with a tiny Haskell program:

-- blows up if you unset PATH
import System.Directory
main = findExecutable "diff"

The good news is that you can catch the exception that findExecutable throws.

Looks like some fairly straightforward improvements to add to Darcs.External

Any new news on this bug? 
Perhaps it may be wiser to use a default path if there is none available
as a fix?
That would be very simple to implement, and could be done per-platform.
A worse case could use the path of the darcs executable.