contrib/plan9/9diff

context: switch ctx() use to changectx()

I added `ctx()` to `overlayworkingfilectx`, (and before that, `absentfilectx`),
because `absentfilectx` had reference to this function in its `cmp()` function.

But the standard is actually `changectx()`, and no other class implements
`ctx()`. So let's use the standard name.

(As a result, I'm not sure that part of the `absentfilectx` comparator ever
worked! It was written before I added either function.)

This will be necessary in the next patch.

Differential Revision: https://phab.mercurial-scm.org/D1211

#!/bin/rc
# 9diff - Mercurial extdiff wrapper for diff(1)

rfork e

fn getfiles {
	cd $1 &&
	for(f in `{du -as | awk '{print $2}'})
		test -f $f && echo `{cleanname $f}
}

fn usage {
	echo >[1=2] usage: 9diff [diff options] parent child root
	exit usage
}

opts=()
while(~ $1 -*){
	opts=($opts $1)
	shift
}
if(! ~ $#* 3)
	usage

# extdiff will set the parent and child to a single file if there is
# only one change. If there are multiple changes, directories will be
# set. diff(1) does not cope particularly with directories; instead we
# do the recursion ourselves and diff each file individually.
if(test -f $1)
	diff $opts $1 $2
if not{
	# extdiff will create a snapshot of the working copy to prevent
	# conflicts during the diff. We circumvent this behavior by
	# diffing against the repository root to produce plumbable
	# output. This is antisocial.
	for(f in `{sort -u <{getfiles $1} <{getfiles $2}}){
		file1=$1/$f; test -f $file1 || file1=/dev/null
		file2=$3/$f; test -f $file2 || file2=/dev/null
		diff $opts $file1 $file2
	}
}
exit ''