Explicitly specify --patch-format in git-am calls

The sources of mbox patches fed to git-am are 1) threads downloaded
from a public-inbox HTTP instance, 2) mboxes generated via
piem-mid-to-thread-functions, and 3) those generated via
piem-am-ready-mbox-functions.  The first source should always be
mboxrd.  For the second, piem-notmuch-mid-to-thread is currently the
only function suitable for piem-mid-to-thread-functions, and it uses
mboxrd.  The third source is a mix between mbox and mboxrd.

By default, git-am tries to auto-detect the patch format, but let's
explicitly specify --patch-format to avoid any incorrect guesses.

Message-Id: <20200810020704.30150-1-kyle@kyleam.com>

4 files changed, 49 insertions, 30 deletions

diff --git a/piem-b4.el b/piem-b4.el
index d1ec157..3381b01 100644
--- a/piem-b4.el
+++ b/piem-b4.el
@@ -126,6 +126,7 @@ am-ready mbox, feed the result to `git am'."
                 (piem-b4--get-am-files mid coderepo args))
                (default-directory coderepo))
     (piem-am mbox-file
+             nil
              (with-temp-buffer
                (insert-file-contents (or cover mbox-file))
                (piem-extract-mbox-info))
diff --git a/piem-gnus.el b/piem-gnus.el
index fcfb08e..9e42185 100644
--- a/piem-gnus.el
+++ b/piem-gnus.el
@@ -77,9 +77,10 @@ message itself if it looks like a patch."
                                      (point-min) (point-max)))))
                            gnus-article-mime-handles))))
         (when patches
-          (lambda ()
-            (dolist (patch patches)
-              (insert patch))))))
+          (list (lambda ()
+                  (dolist (patch patches)
+                    (insert patch)))
+                "mbox"))))
      (gnus-article-buffer
       (let ((patch (with-current-buffer gnus-article-buffer
                      (save-restriction
@@ -89,7 +90,8 @@ message itself if it looks like a patch."
                             (buffer-substring-no-properties
                              (point-min) (point-max)))))))
         (when patch
-          (lambda () (insert patch))))))))
+          (list (lambda () (insert patch))
+                "mbox")))))))
 
 ;;;###autoload
 (define-minor-mode piem-gnus-mode
diff --git a/piem-notmuch.el b/piem-notmuch.el
index 1e4dbb2..c9c3bed 100644
--- a/piem-notmuch.el
+++ b/piem-notmuch.el
@@ -88,9 +88,10 @@ message itself if it looks like a patch."
                                      (plist-get part :content)))
                               (plist-get body :content)))))
            (when patches
-             (lambda ()
-               (dolist (patch patches)
-                 (insert patch))))))))))
+             (list (lambda ()
+                     (dolist (patch patches)
+                       (insert patch)))
+                   "mbox"))))))))
 
 ;;;###autoload
 (define-minor-mode piem-notmuch-mode
diff --git a/piem.el b/piem.el
index 6dc531d..e70c259 100644
--- a/piem.el
+++ b/piem.el
@@ -91,14 +91,17 @@ message ID associated with the current buffer or nil."
 Each function should accept one argument, the message ID.  If the
 function knows how to create an mbox for the message ID, it
 should return a function that takes no arguments and inserts the
-mbox's contents in the current buffer."
+mbox's contents (in mboxrd format) in the current buffer."
   :type 'hook)
 
 (defcustom piem-am-ready-mbox-functions nil
   "Functions tried to get an mbox to be fed to `git am'.
 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."
+arguments and inserts the mbox's contents in the current buffer.
+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)
 
 (defcustom piem-add-message-id-header nil
@@ -333,13 +336,16 @@ intended to be used by libraries implementing a function for
             (insert (format "Message-Id: <%s>\n" mid))))))))
 
 (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))
       (with-current-buffer buffer
         (funcall fn)
         (setq has-content (< 1 (point-max)))
@@ -347,7 +353,7 @@ Callers are responsible for killing the buffer."
           (goto-char (point-min))
           (piem--insert-message-id-header mid)))
       (if has-content
-          buffer
+          (list buffer format)
         (kill-buffer buffer)
         nil))))
 
@@ -524,24 +530,31 @@ in `piem-default-branch-function'."
 (defvar piem-am-args (list "--scissors" "--3way"))
 
 ;;;###autoload
-(defun piem-am (mbox &optional info coderepo)
+(defun piem-am (mbox &optional format info coderepo)
   "Feed an am-ready mbox to `git am'.
 
 MBOX is a buffer whose contents are an am-ready mbox (obtained
-via `piem-am-ready-mbox' when called interactively).  INFO is a
-plist that with information to help choose a default branch name
-or starting point (see `piem-default-branch-function' for a list
-of possible properties).
+via `piem-am-ready-mbox' when called interactively).  FORMAT
+controls the value passed as the --patch-format option of `git
+am'.  \"mbox\" and \"mboxrd\" are valid values, and \"mboxrd\" is
+the default.
+
+INFO is a plist that with information to help choose a default
+branch name or starting point (see `piem-default-branch-function'
+for a list of possible properties).
 
 If CODEREPO is given, switch to this directory before calling
 `git am'."
   (interactive
-   (let ((mbox (or (piem-am-ready-mbox)
-                   (user-error
-                    "Could not find am-ready mbox for current buffer"))))
+   (pcase-let ((`(,mbox ,format)
+                (or (piem-am-ready-mbox)
+                    (user-error
+                     "Could not find am-ready mbox for current buffer"))))
      (list mbox
+           format
            (piem-extract-mbox-info mbox)
            (piem-inbox-coderepo-maybe-read))))
+  (setq format (or format "mboxrd"))
   (let ((default-directory (or coderepo default-directory)))
     (let ((new-branch (read-string
                        "New branch (empty for detached): "
@@ -559,11 +572,13 @@ If CODEREPO is given, switch to this directory before calling
                        (list "-b" new-branch))
                      (and (not (string-blank-p base))
                           (list base)))))
-    (if (bufferp mbox)
-        (apply #'piem-process-call-with-buffer-input
-               nil mbox piem-git-executable "am" piem-am-args)
-      (apply #'piem-process-call nil piem-git-executable "am"
-             (append piem-am-args (list mbox))))
+    (let ((args (cons (concat "--patch-format=" format)
+                      piem-am-args)))
+      (if (bufferp mbox)
+          (apply #'piem-process-call-with-buffer-input
+                 nil mbox piem-git-executable "am" args)
+        (apply #'piem-process-call nil piem-git-executable "am"
+               (append args (list mbox)))))
     (if (and piem-use-magit
              (fboundp 'magit-status-setup-buffer))
         (magit-status-setup-buffer)