Move commands.forget over to using new walk code. With no names, it now recursively forgets everything, as is the default behaviour of other commands. And prints the names of all files it hasn't specifically been told to forget.

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "0 0"

echo 123 > b
hg add b
hg diff | sed "s/\(\(---\|+++\) [^ \t]*\)[ \t].*/\1/"

hg diff -r tip | sed "s/\(\(---\|+++\) [^ \t]*\)[ \t].*/\1/"