$ branches=.hg/cache/branchheads

  $ echo '[extensions]' >> $HGRCPATH

  $ echo 'mq =' >> $HGRCPATH

  $ show_branch_cache()

  > {

  >     # force cache (re)generation

  >     hg log -r does-not-exist 2> /dev/null

  >     hg log -r tip --template 'tip: {rev}\n'

  >     if [ -f $branches ]; then

  >       sort $branches

  >     else

  >       echo No branch cache

  >     fi

  >     if [ "$1" = 1 ]; then

  >       for b in foo bar; do

  >         hg log -r $b --template "branch $b: "'{rev}\n'

  >       done

  >     fi

  > }

  $ hg init a

  $ cd a

  $ hg qinit -c

mq patch on an empty repo

  $ hg qnew -d '0 0' p1

  $ show_branch_cache

  tip: 0

  No branch cache

  $ echo > pfile

  $ hg add pfile

  $ hg qrefresh -m 'patch 1'

  $ show_branch_cache

  tip: 0

some regular revisions

  $ hg qpop

  popping p1

  patch queue now empty

  $ echo foo > foo

  $ hg add foo

  $ echo foo > .hg/branch

  $ hg ci -m 'branch foo'

  $ echo bar > bar

  $ hg add bar

  $ echo bar > .hg/branch

  $ hg ci -m 'branch bar'

  $ show_branch_cache

  tip: 1

  c229711f16da3d7591f89b1b8d963b79bda22714 1

  c229711f16da3d7591f89b1b8d963b79bda22714 bar

  dc25e3827021582e979f600811852e36cbe57341 foo

add some mq patches

  $ hg qpush

  applying p1

  now at: p1

  $ show_branch_cache

  tip: 2

  c229711f16da3d7591f89b1b8d963b79bda22714 1

  c229711f16da3d7591f89b1b8d963b79bda22714 bar

  dc25e3827021582e979f600811852e36cbe57341 foo

  $ hg qnew -d '0 0' p2

  $ echo foo > .hg/branch

  $ echo foo2 >> foo

  $ hg qrefresh -m 'patch 2'

  $ show_branch_cache 1

  tip: 3

  dc25e3827021582e979f600811852e36cbe57341 foo

  branch foo: 3

  branch bar: 2

removing the cache

  $ rm $branches

  $ show_branch_cache 1

  tip: 3

  c229711f16da3d7591f89b1b8d963b79bda22714 1

  c229711f16da3d7591f89b1b8d963b79bda22714 bar

  dc25e3827021582e979f600811852e36cbe57341 foo

  branch foo: 3

  branch bar: 2

importing rev 1 (the cache now ends in one of the patches)

  $ hg qimport -r 1 -n p0

  $ show_branch_cache 1

  tip: 3

  c229711f16da3d7591f89b1b8d963b79bda22714 1

  c229711f16da3d7591f89b1b8d963b79bda22714 bar

  dc25e3827021582e979f600811852e36cbe57341 foo

  branch foo: 3

  branch bar: 2

  $ hg log -r qbase --template 'qbase: {rev}\n'

  qbase: 1

detect an invalid cache

  $ hg qpop -a

  popping p2

  popping p1

  popping p0

  patch queue now empty

  $ hg qpush -a

  applying p0

  applying p1

  applying p2

  now at: p2

  $ show_branch_cache

  tip: 3

  dc25e3827021582e979f600811852e36cbe57341 0

  dc25e3827021582e979f600811852e36cbe57341 foo