templates: add filter to reverse list
The filter supports only lists because for lists, it’s straightforward to
implement. Reversing text doesn’t seem very useful and is hard to implement.
Reversing the bytes would break multi-bytes encodings. Reversing the code
points would break characters consisting of multiple code points. Reversing
graphemes is non-trivial without using a library not included in the standard
library.
$ cat > unix2mac.py <<EOF
> import sys
>
> for path in sys.argv[1:]:
> data = open(path, 'rb').read()
> data = data.replace(b'\n', b'\r')
> open(path, 'wb').write(data)
> EOF
$ hg init
$ echo '[hooks]' >> .hg/hgrc
$ echo 'pretxncommit.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
$ echo 'pretxnchangegroup.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
$ cat .hg/hgrc
[hooks]
pretxncommit.cr = python:hgext.win32text.forbidcr
pretxnchangegroup.cr = python:hgext.win32text.forbidcr
$ echo hello > f
$ hg add f
$ hg ci -m 1
$ "$PYTHON" unix2mac.py f
$ hg ci -m 2
attempt to commit or push text file(s) using CR line endings
in dea860dc51ec: f
transaction abort!
rollback completed
abort: pretxncommit.cr hook failed
[40]
$ hg cat f | f --hexdump
0000: 68 65 6c 6c 6f 0a |hello.|
$ f --hexdump f
f:
0000: 68 65 6c 6c 6f 0d |hello.|