Add githooks from alpine (MR 4008)

Get the githooks from alpine, with the following changes:

* Make it possible to parse the additionally nested "device" folder
  with the exceptions mentioned in our COMMITSTYLE
* Ignore "device/*" as a possible prefix for the commit
* Replace abuild references with pmbootstrap

Relates #2055
[ci:skip-build]: already built successfully in CI

.githooks/pre-commit

@@ -0,0 +1,119 @@
+#!/bin/sh
+#
+# This hook checks that all local sources specified in the staged APKBUILDs
+# are staged too or already committed and that checksums are correct.
+#
+set -eu
+
+# Maximal allowed size (in bytes) of a file.
+FILE_SIZE_LIMIT=262144  # 256 kiB
+
+
+if ! command -v sha512sum >/dev/null; then
+	# macOS / BSDs (?) don't have sha512sum, but shasum.
+	alias sha512sum='shasum -a 512'
+fi
+
+error() {
+	printf '\033[0;31mpre-commit:\033[0m %s\n' "$1" >&2  # red
+}
+
+# Prints paths of created or modified files being committed.
+changed_files() {
+	git diff-index \
+		--name-only \
+		--cached \
+		--diff-filter=ACMR HEAD \
+		-- "$@"
+}
+
+# Prints file names and checksums (in format <SHA-512>:<filename>) of local
+# sources specified in the APKBUILD ($1).
+apkbuild_local_sources() {
+	apkbuild="$1"
+
+	set +eu
+	. "$apkbuild" || {
+		error "$apkbuild is invalid"
+		return 1
+	}
+	set -eu
+
+	status=0
+	: ${source:=""}
+	for src in $source; do
+		# Skip remote sources.
+		case "$src" in */*) continue;; esac
+
+		echo "$sha512sums" | awk -v src="$src" '
+				{ if ($2 == src) { ok=1; print($2 ":" $1) } }
+				END { if (ok != 1) exit 1 }' || {
+			status=1
+			error "${apkbuild%/*}: file \"$src\" is missing in \$sha512sums (hint: run pmbootstrap checksum)"
+		}
+	done
+
+	return $status
+}
+
+# check if given object is a symlink
+is_symlink() {
+	test "$(git ls-files --stage "$1" | awk '{print $1}')" = "120000"
+}
+
+# Checks that all local sources specified in the APKBUILD file ($1) are
+# available in git tree and checksums are correct.
+check_local_sources() {
+	local apkbuild="$1"
+	local startdir="${apkbuild%/*}"
+	local status=0
+	local checksum_act checksum_exp content filename line sources
+
+	sources=$(apkbuild_local_sources "$apkbuild")
+	for line in $sources; do
+		filename=${line%%:*}
+		checksum_exp=${line#*:}
+
+		if ! git cat-file -e ":$startdir/$filename" 2>/dev/null; then
+			error "$startdir: missing file \"$filename\""
+			status=1
+			continue
+		fi
+
+		if is_symlink ":$startdir/$filename"; then
+			continue
+		fi
+
+		checksum_act=$(git show ":$startdir/$filename" | sha512sum)
+		if [ "$checksum_act" != "$checksum_exp  -" ]; then
+			local cmd="pmbootstrap checksum $(basename "$startdir")"
+			error "$startdir: bad checksum for file \"$filename\" (hint: run $cmd)"
+			status=1
+		fi
+	done
+
+	return $status
+}
+
+# Checks if the file ($1) being committed is not bigger than FILE_SIZE_LIMIT.
+check_file_size() {
+	local path="$1"
+	local size
+
+	size=$(git cat-file -s ":$path")
+	if [ $size -gt $FILE_SIZE_LIMIT ]; then
+		local size_kb=$(( size / 1024 ))
+
+		error "file \"$path\" is quite big ($(( size / 1024 )) kiB), better put a remote url in source="
+		return 1
+	fi
+}
+
+
+for apkbuild in $(changed_files '**/APKBUILD'); do
+	check_local_sources "$apkbuild"
+done
+
+for path in $(changed_files); do
+	check_file_size "$path"
+done

.githooks/prepare-commit-msg

@@ -0,0 +1,49 @@
+#!/bin/sh
+#
+# This hook adds prefix "<repo>/<pkgname>: " to the commit message when
+# committing changes of a single package.
+#
+MSG_FILE="$1"
+SOURCE="$2"
+
+longest_common_prefix() {
+	awk -F/ '
+		(NR == 1) { split($0, prefix); prefix_len = NF }
+		(NR > 1) {
+			for (i = 1; i <= prefix_len; i++) {
+				if (prefix[i] != $i) {
+					prefix_len = i - 1; break
+				}
+			}
+		}
+		(prefix_len == 0) { exit }
+		END {
+			res = prefix[1]
+			for (i = 2; i <= prefix_len; i++) {
+				res = res FS prefix[i]
+			}
+			print(res)
+		}'
+}
+
+prepend_msg() {
+	local prefix="$1"
+
+	printf '%s\n%s\n' "$prefix" "$(cat "$MSG_FILE")" > "$MSG_FILE"
+}
+
+
+# Do nothing if message has been given using -m, template, merge etc.
+[ -z "$SOURCE" ] || exit 0
+
+lcp=$(git diff-index --name-only --cached HEAD | longest_common_prefix)
+
+case "$lcp" in
+	device/*/*) prepend_msg "$(echo "$lcp" | cut -d/ -f3): ";;
+	# Multiple packages touched for same device category
+	# More logic could be added to detect if they all belong to same device
+	device/*)  ;;
+	[^.]*/*) prepend_msg "$(echo "$lcp" | cut -d/ -f1-2): ";;
+esac
+
+exit 0