--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/discovery-helper.sh	Wed Nov 28 05:06:58 2018 +0100
@@ -0,0 +1,64 @@
+#!/bin/bash
+#
+# produces two repositories with different common and missing subsets
+#
+#   $ discovery-helper.sh REPO NBHEADS DEPT
+#
+# The Goal is to produce two repositories with some common part and some
+# exclusive part on each side. Provide a source repository REPO, it will
+# produce two repositories REPO-left and REPO-right.
+#
+# Each repository will be missing some revisions exclusive to NBHEADS of the
+# repo topological heads. These heads and revisions exclusive to them (up to
+# DEPTH depth) are stripped.
+#
+# The "left" repository will use the NBHEADS first heads (sorted by
+# description). The "right" use the last NBHEADS one.
+#
+# To find out how many topological heads a repo has, use:
+#
+#   $ hg heads -t -T '{rev}\n' | wc -l
+#
+# Example:
+#
+#  The `pypy-2018-09-01` repository has 192 heads. To produce two repositories
+#  with 92 common heads and ~50 exclusive heads on each side.
+#
+#    $ ./discovery-helper.sh pypy-2018-08-01 50 10
+
+set -euo pipefail
+
+if [ $# -lt 3 ]; then
+     echo "usage: `basename $0` REPO NBHEADS DEPTH"
+     exit 64
+fi
+
+repo="$1"
+shift
+
+nbheads="$1"
+shift
+
+depth="$1"
+shift
+
+leftrepo="${repo}-left"
+rightrepo="${repo}-right"
+
+left="first(sort(heads(all()), 'desc'), $nbheads)"
+right="last(sort(heads(all()), 'desc'), $nbheads)"
+
+leftsubset="ancestors($left, $depth) and only($left, heads(all() - $left))"
+rightsubset="ancestors($right, $depth) and only($right, heads(all() - $right))"
+
+echo '### building left repository:' $left-repo
+echo '# cloning'
+hg clone --noupdate "${repo}" "${leftrepo}"
+echo '# stripping' '"'${leftsubset}'"'
+hg -R "${leftrepo}" --config extensions.strip= strip --rev "$leftsubset" --no-backup
+
+echo '### building right repository:' $right-repo
+echo '# cloning'
+hg clone --noupdate "${repo}" "${rightrepo}"
+echo '# stripping:' '"'${rightsubset}'"'
+hg -R "${rightrepo}" --config extensions.strip= strip --rev "$rightsubset" --no-backup