[PATCH 2/4] piem-am-ready-mbox: Adjust header regex for format-patch change

[Kyle Meyer <kyle@kyleam.com>]

As of git.git's ba4324c4e1 (e-mail workflow: Message-ID is spelled
with ID in both capital letters, 2023-04-03), git-format-patch inserts
a Message-ID header instead of Message-Id.  Teach
piem--insert-message-id-header to look for either variants when it
checks for an existing header.

Another option would be to ignore the header case entirely.  However,
piem--insert-message-id-header is intended to work only for
format-patch output, so stick with the stricter header matching.
---
 piem.el             |  5 ++++-
 tests/piem-tests.el | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/piem.el b/piem.el
index 63c358a2..9dc7f3e3 100644
--- a/piem.el
+++ b/piem.el
@@ -601,8 +601,11 @@ (defun piem--insert-message-id-header (mid)
                             (rx line-start (zero-or-one space) line-end))))
             (cond
              ((looking-at-p
+               ;; git-format-patch switched to "Message-ID" spelling
+               ;; in v2.41.
                (rx line-start
-                   "Message-Id: <" (one-or-more not-newline) ">"
+                   "Message-" (or "Id" "ID")
+                   ": <" (one-or-more not-newline) ">"
                    line-end))
               (throw 'has-message-id nil))
              ((looking-at-p
diff --git a/tests/piem-tests.el b/tests/piem-tests.el
index 79d8591e..6f39a53e 100644
--- a/tests/piem-tests.el
+++ b/tests/piem-tests.el
@@ -179,6 +179,24 @@ (ert-deftest piem--insert-message-id-header ()
   (should-not
    (with-temp-buffer
      (piem--insert-message-id-header "msg@id")))
+  (should-not
+   (string-match-p
+    "Message-Id: <msg@id>"
+    (with-temp-buffer
+      (insert "\
+From 0d732713af1f3fb48b37430e2cd0a3033cea14f3 Mon Sep 17 00:00:00 2001
+From: Foo Bar <f@example.com>
+Message-ID: <existing@id>
+Date: Fri, 22 Jan 2021 22:35:58 -0500
+Subject: [PATCH] a
+
+---
+ a | 1 +
+ 1 file changed, 1 insertion(+)
+ create mode 100644 a")
+      (goto-char (point-min))
+      (piem--insert-message-id-header "msg@id")
+      (buffer-string))))
   (should
    (string-match-p
     (concat
-- 
2.39.2