handle .pacnew files automatically on Arch Linux

By installing a libalpm hook, as supported by Pacman 5.0+.

Makefile

@@ -41,5 +41,6 @@ install: default conf/holorc conf/holorc.holo-files src/holo-test util/autocompl
 	install -D -m 0644 build/man/holo-files.8            "$(DESTDIR)/usr/share/man/man8/holo-files.8"
 	install -D -m 0644 build/man/holo-test.7             "$(DESTDIR)/usr/share/man/man7/holo-test.7"
 	install -D -m 0644 build/man/holo-plugin-interface.7 "$(DESTDIR)/usr/share/man/man7/holo-plugin-interface.7"
+	env DESTDIR=$(DESTDIR) ./src/distribution-integration/install.sh
 
 .PHONY: prepare-build test check install

src/distribution-integration/alpm-hook.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+set -euo pipefail
+
+# enumerate files that are managed by holo-files
+holo scan --short | grep '^file:' | cut -d: -f2- | sort > /tmp/files-managed-by-holo
+
+# changed files come from stdin (but without leading slash!); find files
+# managed by Holo among these
+sort | sed 's+^+/+' | comm -12 - /tmp/files-managed-by-holo | sed 's/^/file:/' | xargs holo apply
+
+# cleanup
+rm /tmp/files-managed-by-holo

src/distribution-integration/alpm.hook

@@ -0,0 +1,11 @@
+[Trigger]
+Operation = Upgrade
+Type = File
+Target = *
+
+[Action]
+Description = Checking for .pacnew files that can be resolved by Holo...
+When = PostTransaction
+Depends = holo
+Exec = /usr/lib/holo/alpm-hook-resolve-pacnew
+NeedsTargets

src/distribution-integration/install.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+CURRENT_DIR="$(dirname $0)"
+
+# check distribution and install appropriate integrations
+[ -f /etc/os-release ] && source /etc/os-release || source /usr/lib/os-release
+DIST_IDS="$(echo "$ID $ID_LIKE" | tr ' ' ',')"
+
+case ",$DIST_IDS," in
+    *,arch,*)
+        set -ex
+        install -D -m 0644 "${CURRENT_DIR}/alpm.hook"    "${DESTDIR}/usr/share/libalpm/hooks/01-holo-resolve-pacnew.hook"
+        install -D -m 0755 "${CURRENT_DIR}/alpm-hook.sh" "${DESTDIR}/usr/lib/holo/alpm-hook-resolve-pacnew"
+        ;;
+    *)
+        echo No specialized integration for this distribution.
+        ;;
+esac