[PATCH] Fix handling of -am-ready-mbox values

[Kyle Meyer <kyle@kyleam.com>]

Kyle Meyer writes:

>  (defun piem-am-ready-mbox ()
> -  "Return buffer containing an am-ready mbox.
> -Callers are responsible for killing the buffer."
> -  (when-let ((fn (run-hook-with-args-until-success
> -                  'piem-am-ready-mbox-functions)))
> -    (let ((buffer (generate-new-buffer " *piem am-ready mbox*"))
> -          (mid (and piem-add-message-id-header (piem-mid)))
> -          has-content)
> +  "Generate a buffer containing an am-ready mbox.
> +The return value is (BUFFER FORMAT), where FORMAT is either
> +\"mbox\" or \"mboxrd\".  Callers are responsible for killing the
> +buffer."
> +  (when-let ((res (run-hook-with-args-until-success
> +                   'piem-am-ready-mbox-functions)))
> +    (pcase-let ((buffer (generate-new-buffer " *piem am-ready mbox*"))
> +                (`(,fn ,format) (if (listp res) res (list res "mboxrd")))
> +                (mid (and piem-add-message-id-header (piem-mid)))
> +                (has-content nil))

Bah, caught only after applying, but this logic is flawed.  res is a
list even if it doesn't include the format.  The issue shows up in the
text/plain code path of piem-notmuch-am-ready-mbox because it doesn't
explicitly specify a format, relying on mboxrd being the default.

-- >8 --
Subject: [PATCH] Fix handling of -am-ready-mbox values

0ee97e9 (Explicitly specify --patch-format in git-am calls,
2020-08-09) made it possible for a piem-am-ready-mbox-functions member
to specify the format of the mbox by returning (FUNCTION FORMAT).  If
FUNCTION is returned, then mboxrd is supposed to be taken as the
default format.  The handling is broken, though, because
piem-am-ready-mbox tries to detect the (FUNCTION FORMAT) form with
listp, but that of course also returns true when the return value is
simply a function.

Instead, check to see whether the element matches a valid format
value.  Switch from (FUNCTION FORMAT) to (FUNCTION . FORMAT) to make
it more convenient to pull out FORMAT with cdr-safe.
---
 piem-gnus.el    |  4 ++--
 piem-notmuch.el |  2 +-
 piem.el         | 13 ++++++++-----
 3 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/piem-gnus.el b/piem-gnus.el
index 9e42185..244c389 100644
--- a/piem-gnus.el
+++ b/piem-gnus.el
@@ -77,7 +77,7 @@ (defun piem-gnus-am-ready-mbox ()
                                      (point-min) (point-max)))))
                            gnus-article-mime-handles))))
         (when patches
-          (list (lambda ()
+          (cons (lambda ()
                   (dolist (patch patches)
                     (insert patch)))
                 "mbox"))))
@@ -90,7 +90,7 @@ (defun piem-gnus-am-ready-mbox ()
                             (buffer-substring-no-properties
                              (point-min) (point-max)))))))
         (when patch
-          (list (lambda () (insert patch))
+          (cons (lambda () (insert patch))
                 "mbox")))))))
 
 ;;;###autoload
diff --git a/piem-notmuch.el b/piem-notmuch.el
index c9c3bed..29f4d27 100644
--- a/piem-notmuch.el
+++ b/piem-notmuch.el
@@ -88,7 +88,7 @@ (defun piem-notmuch-am-ready-mbox ()
                                      (plist-get part :content)))
                               (plist-get body :content)))))
            (when patches
-             (list (lambda ()
+             (cons (lambda ()
                      (dolist (patch patches)
                        (insert patch)))
                    "mbox"))))))))
diff --git a/piem.el b/piem.el
index e70c259..ece30bd 100644
--- a/piem.el
+++ b/piem.el
@@ -99,7 +99,7 @@ (defcustom piem-am-ready-mbox-functions nil
 The functions are called with no arguments.  If a function knows
 how to create an mbox, it should return a function that takes no
 arguments and inserts the mbox's contents in the current buffer.
-The return value can also be (FUNCTION FORMAT), where FORMAT is
+The return value can also be (FUNCTION . FORMAT), where FORMAT is
 either \"mbox\" or \"mboxrd\" and maps to the --patch-format
 value passed to `git am'.  If unspecified, \"mboxrd\" is used."
   :type 'hook)
@@ -337,13 +337,16 @@ (defun piem--insert-message-id-header (mid)
 
 (defun piem-am-ready-mbox ()
   "Generate a buffer containing an am-ready mbox.
-The return value is (BUFFER FORMAT), where FORMAT is either
+The return value is (BUFFER . FORMAT), where FORMAT is either
 \"mbox\" or \"mboxrd\".  Callers are responsible for killing the
 buffer."
   (when-let ((res (run-hook-with-args-until-success
                    'piem-am-ready-mbox-functions)))
     (pcase-let ((buffer (generate-new-buffer " *piem am-ready mbox*"))
-                (`(,fn ,format) (if (listp res) res (list res "mboxrd")))
+                (`(,fn . ,format)
+                 (if (member (cdr-safe res) '("mbox" "mboxrd"))
+                     res
+                   (cons res "mboxrd")))
                 (mid (and piem-add-message-id-header (piem-mid)))
                 (has-content nil))
       (with-current-buffer buffer
@@ -353,7 +356,7 @@ (defun piem-am-ready-mbox ()
           (goto-char (point-min))
           (piem--insert-message-id-header mid)))
       (if has-content
-          (list buffer format)
+          (cons buffer format)
         (kill-buffer buffer)
         nil))))
 
@@ -546,7 +549,7 @@ (defun piem-am (mbox &optional format info coderepo)
 If CODEREPO is given, switch to this directory before calling
 `git am'."
   (interactive
-   (pcase-let ((`(,mbox ,format)
+   (pcase-let ((`(,mbox . ,format)
                 (or (piem-am-ready-mbox)
                     (user-error
                      "Could not find am-ready mbox for current buffer"))))

base-commit: 0ee97e900f7daef3995284d0b4312c371b3427fa
-- 
2.28.0