rh-utils: add script find-backports.sh

When backporting commits, we should do `git cherry-pick -x`,
so that the commit message contains:
    (cherry picked from commit $SHA)

Similarly, when fixing an actual bug of a previous commit, we
mark the faulty commit with:
    Fixes: $SHA

This script walks through a commit range of a stable branch,
and finds all $BACKPORTED_COMMITS (the sources from where we
cherry-picked).
Then it walks through a commit range of upstream/unstable branch,
and searches for $FIXES of the $BACKPORTED_COMMITS.

Then it prints all $FIXES, that are not yet backported. You probably
should backport those commits as well.

contrib/rh-utils/find-backports.sh

@@ -0,0 +1,87 @@
+#!/bin/bash
+
+die() {
+	echo "$@" >&2
+	exit 1
+}
+
+print_usage() {
+	echo "$0 [REF_BASE REF_STABLE REF_UPSTREAM]"
+	echo "   for example $0 1.1.0-dev~ nm-1-0 master"
+}
+
+ref_exists() {
+	git rev-parse --verify "$1" &> /dev/null
+}
+
+get_cherry_picked_from() {
+	local H="$1"
+	local B
+
+	for B in $(git log -n1 "$H" 2>&1 | sed -n -e 's/.*cherry.picked.*\<\([0-9a-f]\{6,40\}\)\>.*/\1/p'); do
+		if ref_exists "$B"; then
+			echo $B
+
+			# if the original patch was cherry-picked too, continue
+			# recursively.
+			get_cherry_picked_from "$B"
+		fi
+	done
+}
+
+get_backported_all() {
+	local RANGE="$1"
+	local H
+
+	for H in $(git log --pretty="%H" "$RANGE"); do
+	    get_cherry_picked_from "$H"
+	done |
+	sort | uniq
+}
+
+get_fixes() {
+	local RANGE="$1"
+	local BACKPORTED="$2"
+	local H B
+
+	for H in $BACKPORTED; do
+		for B in $(git log --format="%H" --no-walk --grep '[Ff]ixes: *'"${H:0:7}" "$RANGE"); do
+			echo "$B"
+
+			# if commit $B fixes $H, and commit $B was itself backported (cherry-picked),
+			# then also all original versions of $B fix $H.
+			get_cherry_picked_from "$B"
+		done
+	done |
+	sort | uniq
+}
+
+if [[ "$#" != 3 && "$#" != 0 ]]; then
+	print_usage
+	die "Wrong arguments"
+fi
+
+if [[ "$#" == 3 ]]; then
+	REF_BASE="$1"
+	REF_STABLE="$2"
+	REF_UPSTREAM="$3"
+else
+	REF_BASE=1.1.0-dev~
+	REF_STABLE=nm-1-0
+	REF_UPSTREAM=master
+fi
+
+ref_exists "$REF_BASE" || die "Invalid REF_BASE=\"$REF_BASE\""
+ref_exists "$REF_UPSTREAM"  || die "Invalid REF_UPSTREAM=\"$REF_UPSTREAM\""
+ref_exists "$REF_STABLE"  || die "Invalid REF_STABLE=\"$REF_STABLE\""
+
+BACKPORTED="$(get_backported_all "$REF_BASE..$REF_STABLE")"
+
+FIXES="$(get_fixes "$REF_BASE..$REF_UPSTREAM" "$BACKPORTED")"
+
+MISSING_BACKPORTS="$(printf '%s' "$FIXES" | grep $(printf '%s' "$BACKPORTED" | sed 's/^/-e /') - -v)"
+if [ -n "$MISSING_BACKPORTS" ]; then
+	git log -p --no-walk $(echo "$MISSING_BACKPORTS")
+	printf "%s\n" "$MISSING_BACKPORTS"
+fi
+