gnulib-tool: .XXXignore files generation

[Dmitry Selyutin]

Hi again,

that's yet another question on gnulib-tool. Now I'm implementing the code 
which takes care of .gitignore and .cvsignore files, and I must admit that the 
overall algorithm is a bit tricky (perhaps the only reason is that it was 
designed so that it is generic and can be applied both to git and CVS with 
small changes, which is a nice property). Could someone describe how it works? 
As far as I understand, we must iterate over added_files and removed_files so 
that on each iteration we yield the following information:
1. dirname
2. operation
3. basename
4. previous dirname

FWIW, this likely resembles the following in Python:
    added_files = ["lib/bitrotate.c", "m4/cond.m4"]
    removed_files = ["prefix/tests/zerosize-ptr.h", "dir/m4/ctype.m4"]
    items = [tuple(["A"] + list(os.path.split(path))) for path in added_files]
    items += [tuple(["D"] + list(os.path.split(path))) for path in 
removed_files]
    for (head, tail) in zip(items, items[1:]):
        print(head, tail)

This code will lead to the following output:
    ('A', 'lib', 'bitrotate.c') ('A', 'm4', 'cond.m4')
    ('A', 'm4', 'cond.m4') ('D', 'prefix/tests', 'zerosize-ptr.h')
    ('D', 'prefix/tests', 'zerosize-ptr.h') ('D', 'm4', 'ctype.m4')

However, the tricky part is what to do with that information. Could you help 
me on this part, please? Thank you for your help!

-- 
With best regards,
Dmitry Selyutin