When we can't find a .do file, we walk all the way back to the root
directory. When that happens, the root directory is actually searched
twice. This is harmless (since a .do file doesn't exist there anyway)
but causes redo-whichdo to produce the wrong output.
Also, add a test, which I forgot to do when writing whichdo in the
first place.
To make the test work from the root directory, we need a way to
initialize redo without actually creating a .redo directory. Add a
init_no_state() function for that purpose, and split the necessary path
functions into their own module so we can avoid importing builder.py.
If a depends on b which depends on a, redo would just freeze. Now it
aborts with a somewhat helpful error message.
[Updated by apenwarr for coding style and to add a test.]
We already did this in minimal/do, and redo-ifchange already did this, but
plain redo didn't. This made constructs like:
for d in *.x; do
echo "${d%.x}"
done | xargs redo
dangerous, because if there were no matching files, we'd try to 'redo all'.
This includes a fairly detailed test of various known shell bugs from the
autoconf docs.
The idea here is that if redo works on your system, you should be able to
rely on a *good* shell to run your .do files; you shouldn't have to work
around zillions of bugs like autoconf does.
