diff: add --inverse option
Most of the time, one can reverse a diff by swapping the revisions passed with
-r but it happens that if you use the global -R, and diff against the tip of
the current repo, you can't swap the revisions. One use-case for that is
reviewing changes from a bundle before unbundling. One could also pipe the
output of `hg diff` to a command line filter that reverses the diff, but that
would remove the benefit from color diffs. Therefore, having an option in
`hg diff` to reverse a diff is a good thing.
The option flag selection was tricky. GNU patch uses -R/--reverse but -R is
already used as a global option and --reverse would make --rev ambiguous.
#!/bin/sh
hg init
cat > a <<EOF
a
b
c
EOF
hg ci -Am adda
cat > a <<EOF
d
e
f
EOF
hg ci -m moda
hg diff --inverse -r0 -r1
cat >> a <<EOF
g
h
EOF
hg diff --inverse --nodates