AmbiguousCommand is raised too soon. Right now, hg raises AmbiguousCommand as soon as it finds two commands/aliases that start with the substring it's searching for, even though it may still find a full match later on. This is a bit hard to hit on purpose, because hg checks the list of commands in whatever order is returned by table.keys(), which will change when you add an alias to a command. You should be able to hit it by adding an alias "u" to the "identify" command - not that that makes a lot of sense...

#!/bin/sh

hg init

echo foo > a
echo foo > b
hg add a b

hg ci -m "test" -d "0 0"

echo blah > a

hg ci -m "branch a" -d "0 0"

hg co 0

echo blah > b

hg ci -m "branch b" -d "0 0"
HGMERGE=true hg up -m 1

hg ci -m "merge b/a -> blah" -d "0 0"

hg co 1
HGMERGE=true hg up -m 2
hg ci -m "merge a/b -> blah" -d "0 0"

hg log
hg debugindex .hg/00changelog.i

echo

echo 1
hg manifest 1
echo 2
hg manifest 2
echo 3
hg manifest 3
echo 4
hg manifest 4

echo

hg debugindex .hg/data/a.i

hg verify