teams: Add a "get-maintainer" command.

This can be used as a compatibility mode with the get_maintainer.pl Perl
script included in the Linux (or U-Boot) source tree.

* etc/teams.scm.in (git-patch->commit-id): New procedure.
(main) <get-maintainer>: Register new command.  Document it.

Series-changes: 2
- Move newline character (~%) in usage output to the bottom

etc/teams.scm.in

@@ -5,6 +5,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2022 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2022 Mathieu Othacehe <othacehe@gnu.org>
+;;; Copyright © 2022 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -34,6 +35,7 @@
              (ice-9 format)
              (ice-9 regex)
              (ice-9 match)
+             (ice-9 rdelim)
              (guix ui)
              (git))
 
@@ -623,6 +625,15 @@ and REV-END, two git revision strings."
      (const 0))
     files))
 
+(define (git-patch->commit-id file)
+  "Parse the commit ID from the first line of FILE, a patch produced with git."
+  (call-with-input-file file
+    (lambda (port)
+      (let ((m (string-match "^From ([0-9a-f]{40})" (read-line port))))
+        (unless m
+          (error "invalid patch file:" file))
+        (match:substring m 1)))))
+
 
 (define (main . args)
   (match args
@@ -631,6 +642,12 @@ and REV-END, two git revision strings."
     (("cc-members" rev-start rev-end)
      (apply cc (find-team-by-scope
                 (diff-revisions rev-start rev-end))))
+    (("get-maintainer" patch-file)
+     (let* ((rev-end (git-patch->commit-id patch-file))
+            (rev-start (string-append rev-end "^")))
+       (apply main "list-members"
+              (map (compose symbol->string team-id)
+                   (find-team-by-scope (diff-revisions rev-start rev-end))))))
     (("list-teams" . args)
      (list-teams))
     (("list-members" . team-names)
@@ -646,6 +663,7 @@ Commands:
   cc <team-name>            get git send-email flags for cc-ing <team-name>
   cc-members <start> <end>  cc teams related to files changed between revisions
   list-teams                list teams and their members
-  list-members <team-name>  list members belonging to <team-name>~%"))))
+  list-members <team-name>  list members belonging to <team-name>
+  get-maintainer <patch>    compatibility mode with Linux get_maintainer.pl~%"))))
 
 (apply main (cdr (command-line)))