From 29c44e1f1e505071df35335b144e2d8bef7219c9 Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@1wt.eu>
Date: Mon, 16 May 2016 17:01:12 +0200
Subject: [PATCH] SCRIPTS: make git-show-backports capable of limiting its
 history

When comparing very different branches, it can take a very long time
to scan all commits from the very old common ancestor (eg: haproxy
1.4 to 1.7). Now it is possible to specify a range of commits instead
of a specific branch, and the analysis will be limited to this range
for all commits. The user is responsible for ensuring that the range
covers all possible backports from base to ref, otherwise some of them
may be reported missing while they are not.

This also works with linux kernels, for example :

   git-show-backports -u -q -m -r v3.14.69 -b v3.14.65 v3.10.101..HEAD
---
 scripts/git-show-backports | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/scripts/git-show-backports b/scripts/git-show-backports
index d8854bf82..cbe40bbc2 100755
--- a/scripts/git-show-backports
+++ b/scripts/git-show-backports
@@ -28,7 +28,8 @@
 #   show-backports -q -m -r hapee-r2 hapee-r1
 
 
-USAGE="Usage: ${0##*/} [-q] [-m] [-u] [-r reference] [-l logexpr] [-s subject] [-b base] branch [...]"
+USAGE="Usage: ${0##*/} [-q] [-m] [-u] [-r reference] [-l logexpr] [-s subject] [-b base] {branch|range} [...]"
+BASES=( )
 BRANCHES=( )
 REF=master
 BASE=
@@ -140,7 +141,22 @@ while [ -n "$1" -a -z "${1##-*}" ]; do
 	esac
 done
 
-BRANCHES=( "$@" )
+# branches may also appear as id1..id2 to limit the history instead of looking
+# back to the common base. The field is left empty if not set.
+BRANCHES=( )
+BASES=( )
+while [ $# -gt 0 ]; do
+	branch="${1##*..}"
+	if [ "$branch" == "$1" ]; then
+		base=""
+	else
+		base="${1%%..*}"
+	fi
+	BASES[${#BRANCHES[@]}]="$base"
+	BRANCHES[${#BRANCHES[@]}]="$branch"
+	shift
+done
+
 if [ ${#BRANCHES[@]} = 0 ]; then
 	die "$USAGE"
 fi
@@ -170,12 +186,18 @@ rm -f "$WORK/${REF//\//_}"
 git log --reverse ${LOGEXPR:+--grep $LOGEXPR} --pretty="%H %s" "$BASE".."$REF" | grep "${SUBJECT}" > "$WORK/${branch//\//_}" > "$WORK/${REF//\//_}"
 
 # for each branch, enumerate all commits and their ancestry
-for branch in "${BRANCHES[@]}"; do
+
+branch_num=0;
+while [ $branch_num -lt "${#BRANCHES[@]}" ]; do
+	branch="${BRANCHES[$branch_num]}"
+	base="${BASES[$branch_num]}"
+	base="${base:-$BASE}"
 	rm -f "$WORK/${branch//\//_}"
-	git log --reverse --pretty="%H %s" "$BASE".."$branch" | grep "${SUBJECT}" | while read h subject; do
+	git log --reverse --pretty="%H %s" "$base".."$branch" | grep "${SUBJECT}" | while read h subject; do
 		echo "$h" $(git log -1 --pretty --format=%B "$h" | \
 			sed -n 's/^commit \([^)]*\) upstream\.$/\1/p;s/^(cherry picked from commit \([^)]*\))/\1/p')
 	done > "$WORK/${branch//\//_}"
+	(( branch_num++ ))
 done
 
 count=0