git-email: Add function to extract multi-line subjects.

‘git-format-patch’ adds a newline in the subject if it is too long, if
we just use ‘git-email--extract-header’, part of the subject is going
to be cut off.

  Subject: [PATCH] services: configuration: Show default value when it is a
   package.

* git-email.el (git-email-subject-regexp): New variable.
  (git-email--extract-subject): New function.
  (git-email--extract-header): Use it.

Signed-off-by: Xinglu Chen <public@yoctocell.xyz>

1 files changed, 31 insertions, 6 deletions

diff --git a/git-email.el b/git-email.el
index 0fc0e43..fedd03d 100644
--- a/git-email.el
+++ b/git-email.el
@@ -231,13 +231,38 @@ Falls back to `default-directory'."
 
 ;;;; Get contents from patch
 (defun git-email--extract-header (header)
-  "Extract HEADER from current buffer."
+  "Extract HEADER from the current buffer."
   (goto-char (point-min))
-  (buffer-substring-no-properties
-   (if (re-search-forward (format " *%s: +" header) nil t)
-       (point)
-     (point-at-eol))
-   (point-at-eol)))
+  (if (eq header 'subject)
+      (git-email--extract-subject)
+    (buffer-substring-no-properties
+     (if (re-search-forward (format " *%s: +" header) nil t)
+         (point)
+       (point-at-eol))
+     (point-at-eol))))
+
+(defvar git-email-subject-regexp
+  (rx bol "Subject:"
+      (zero-or-more space) "["
+      (zero-or-more (not (any "]" "\n")))
+      "PATCH"
+      (zero-or-more (not (any "]" "\n")))
+      "]" (one-or-more space)
+      (one-or-more not-newline)
+      (or (and eol (= 2 space)
+               (one-or-more (not (any "\n" "\t" "$"))) eol)
+          eol)))
+
+(defun git-email--extract-subject ()
+  "Extract the subject from the current buffer.  git-format-patch
+will add a newline in the subject if the subject is too long.
+Just using `git-email--extract-header' would result in part of
+the subject being cut of.  See what I did there?  ;-)"
+  (let ((string (buffer-substring-no-properties (point-min) (point-max))))
+    (string-match git-email-subject-regexp string)
+    (string-remove-prefix
+     "Subject: " (replace-regexp-in-string
+                  "\n" "" (match-string-no-properties 0 string)))))
 
 (defun git-email--extract-headers (patch-file)
   "Extract headers from PATCH-FILE.