Add a script to add git branches for each channel.

maintainers/scripts/update-channel-branches.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+: ${NIXOS_CHANNELS:=https://nixos.org/channels/}
+
+# Find the name of all channels which are listed in the directory.
+for channelName in : $(curl -s $NIXOS_CHANNELS | sed -n '/folder/ { s,.*href=",,; s,/".*,,; p }'); do
+    test "$channelName" = : && continue;
+
+    # Do not follow redirections, such that we can extract the
+    # short-changeset from the name of the directory where we are
+    # redirected to.
+    sha1=$(curl -s --max-redirs 0 $NIXOS_CHANNELS$channelName | sed -n '/has moved/ { s,.*\.\([a-z0-9A-Z]*\)".*,\1,; p; }')
+    test -z "$sha1" -o -z "$channelName" && continue;
+
+    # Update the local channels/* branches to be in-sync with the
+    # channel references.
+    git update-ref refs/heads/channels/$channelName $sha1
+done