discovery-helper: add an extra argument to generate only one repo

This is useful to generate left and right in parallel when dealing with very
large repositories.

contrib/perf-utils/discovery-helper.sh

@@ -28,8 +28,12 b''
 
 set -euo pipefail
 
+printusage () {
+     echo "usage: `basename $0` REPO NBHEADS DEPTH [left|right]" >&2
+}
+
 if [ $# -lt 3 ]; then
-     echo "usage: `basename $0` REPO NBHEADS DEPTH"
+    printusage
      exit 64
 fi
 
@@ -42,6 +46,24 b' shift'
 depth="$1"
 shift
 
+doleft=1
+doright=1
+if [ $# -gt 1 ]; then
+    printusage
+    exit 64
+elif [ $# -eq 1 ]; then
+    if [ "$1" == "left" ]; then
+        doleft=1
+        doright=0
+    elif [ "$1" == "right" ]; then
+        doleft=0
+        doright=1
+    else
+        printusage
+        exit 64
+    fi
+fi
+
 leftrepo="${repo}-${nbheads}h-${depth}d-left"
 rightrepo="${repo}-${nbheads}h-${depth}d-right"
 
@@ -52,17 +74,25 b' leftsubset="ancestors($left, $depth) and'
 rightsubset="ancestors($right, $depth) and only($right, heads(all() - $right))"
 
 echo '### creating left/right repositories with missing changesets:'
+if [ $doleft -eq 1 ]; then
 echo '# left  revset:' '"'${leftsubset}'"'
+fi
+if [ $doright -eq 1 ]; then
 echo '# right revset:' '"'${rightsubset}'"'
+fi
 
+if [ $doleft -eq 1 ]; then
 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
+fi
 
+if [ $doright -eq 1 ]; then
 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
+fi