contributing: add tooling for git send-email

Add a gitconfig target in the Makefile to configure a new clone with
sane defaults:

- set subject prefix
- set correct mailing list address
- enable sendemail.validate
- install sendemail-validate hook

The sendemail-validate hook will make a shallow clone of the current
upstream repo, apply every patch on it and run some checks (a stripped
down version of what is run by the upstream CI).

Add a new check-patches script that verifies that the commit message
actually contains something and that the Signed-off-by trailer from the
patch author is present.

Call check-patches in both the CI and the sendemail-validate hook.

Update CONTRIBUTING.md accordingly.

Signed-off-by: Robin Jarry <robin@jarry.cc>
Acked-by: Tim Culverhouse <tim@timculverhouse.com>

2 files changed, 50 insertions, 0 deletions

diff --git a/contrib/check-patches b/contrib/check-patches
new file mode 100755
index 00000000..738b1816
--- /dev/null
+++ b/contrib/check-patches
@@ -0,0 +1,39 @@
+#!/bin/sh
+
+set -e
+
+revision_range="${1?revision range}"
+
+total=0
+valid=0
+
+for rev in $(git rev-list --reverse "$revision_range"); do
+	total=$((total + 1))
+	title=$(git log --format='%s' -1 "$rev")
+
+	author=$(git log --format='%aN <%aE>' -1 "$rev")
+	git log --format="%(trailers:key=Signed-off-by,only,valueonly)" -1 "$rev" |
+	grep -qFx "$author" || {
+		echo "error: '$title' 'Signed-off-by: $author' trailer is missing" >&2
+		continue
+	}
+
+	body=$(git log --format='%b' -1 "$rev")
+	body=${body%$(git log --format='%(trailers)' -1 "$rev")}
+	if [ "$(echo "$body" | wc -w)" -lt 3 ]; then
+		echo "error: '$title' body has less than three words, please elaborate" >&2
+		continue
+	fi
+
+	echo "ok: '$title'"
+	valid=$((valid + 1))
+done
+
+if [ "$total" -eq 0 ]; then
+	exit 0
+fi
+
+echo "$valid/$total valid patches"
+if [ "$valid" -ne "$total" ]; then
+	exit 1
+fi
diff --git a/contrib/sendemail-validate b/contrib/sendemail-validate
new file mode 100755
index 00000000..1d18e65c
--- /dev/null
+++ b/contrib/sendemail-validate
@@ -0,0 +1,11 @@
+#!/bin/sh
+
+set -e
+
+email="${1?email file}"
+tmp=$(mktemp -d)
+trap "rm -rf -- $tmp" EXIT
+git clone -q --depth=1 "https://git.sr.ht/~rjarry/aerc" "$tmp"
+export GIT_DIR="$tmp/.git"
+git -C "$tmp" am -q3 "$email"
+make -sC "$tmp" check-patches all lint tests