[PATCH] WIP/emacs: replace use of indent-rigidly in notmuch-show

[David Bremner <david@tethera.net>]

Several people have observed that the display of patches in
notmuch-emacs is less than ideal because context lines do not line up
properly with changed lines. The underlying cause is that
indent-rigidly adds space in different places for those lines. In this
commit, indent-rigidly is replaced with a more simple-minded function
that always adds spaces to the beginning of the line.
---

This is not really well tested, and somewhat copy-pasta-ed together
code. Looking at this mail, I see the indentation of the call sites is
not great either.

 emacs/notmuch-show.el | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 4de3e423..50ed6f28 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -29,6 +29,8 @@
 (require 'mailcap)
 (require 'icalendar)
 (require 'goto-addr)
+(require 'rect)
+(require 'cl-lib)
 
 (require 'notmuch-lib)
 (require 'notmuch-tag)
@@ -272,6 +274,23 @@ position of the message in the thread."
 
 ;;; Utilities
 
+;; force all indentation to be spaces at BOL
+;; Based on apply-on-rectangle, from rect.el
+(defun notmuch--indent-rigidly (start end count)
+  (if (<= count 0)
+      (indent-rigidly start end count)
+    (save-excursion
+      (let ((startpt (progn (goto-char start) (line-beginning-position)))
+	    (endpt (progn (goto-char end) (line-end-position)))
+	    (spaces (spaces-string count)))
+	(goto-char startpt)
+	(while
+	    (progn
+	      (insert spaces)
+	      (cl-incf endpt count)
+	      (and (zerop (forward-line 1)) (bolp)
+		   (<= (point) endpt))))))))
+
 (defmacro with-current-notmuch-show-message (&rest body)
   "Evaluate body with current buffer set to the text of current message."
   `(save-excursion
@@ -354,7 +373,7 @@ operation on the contents of the current buffer."
     (with-temp-buffer
       (insert all)
       (when indenting
-	(indent-rigidly (point-min)
+	(notmuch--indent-rigidly (point-min)
 			(point-max)
 			(- (* notmuch-show-indent-messages-width depth))))
       ;; Remove the original header.
@@ -654,7 +673,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 	  inner-parts)
 
     (when notmuch-show-indent-multipart
-      (indent-rigidly start (point) 1)))
+      (notmuch--indent-rigidly start (point) 1)))
   t)
 
 (defun notmuch-show-insert-part-multipart/related (msg part _content-type _nth depth _button)
@@ -667,7 +686,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 	    (notmuch-show-insert-bodypart msg inner-part depth t))
 	  (cdr inner-parts))
     (when notmuch-show-indent-multipart
-      (indent-rigidly start (point) 1)))
+      (notmuch--indent-rigidly start (point) 1)))
   t)
 
 (defun notmuch-show-insert-part-multipart/signed (msg part _content-type _nth depth button)
@@ -683,7 +702,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 	    (notmuch-show-insert-bodypart msg inner-part depth))
 	  inner-parts)
     (when notmuch-show-indent-multipart
-      (indent-rigidly start (point) 1)))
+      (notmuch--indent-rigidly start (point) 1)))
   t)
 
 (defun notmuch-show-insert-part-multipart/encrypted (msg part _content-type _nth depth button)
@@ -701,7 +720,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 	    (notmuch-show-insert-bodypart msg inner-part depth))
 	  inner-parts)
     (when notmuch-show-indent-multipart
-      (indent-rigidly start (point) 1)))
+      (notmuch--indent-rigidly start (point) 1)))
   t)
 
 (defun notmuch-show-insert-part-application/pgp-encrypted (_msg _part _content-type _nth _depth _button)
@@ -715,7 +734,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 	    (notmuch-show-insert-bodypart msg inner-part depth))
 	  inner-parts)
     (when notmuch-show-indent-multipart
-      (indent-rigidly start (point) 1)))
+      (notmuch--indent-rigidly start (point) 1)))
   t)
 
 (defun notmuch-show-insert-part-message/rfc822 (msg part _content-type _nth depth _button)
@@ -734,7 +753,7 @@ will return nil if the CID is unknown or cannot be retrieved."
        ;; Show the body
        (notmuch-show-insert-bodypart msg body depth)
        (when notmuch-show-indent-multipart
-	 (indent-rigidly start (point) 1))
+	 (notmuch--indent-rigidly start (point) 1))
        t))))
 
 (defun notmuch-show-insert-part-text/plain (msg part _content-type _nth depth button)
@@ -942,7 +961,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 	(narrow-to-region part-beg part-end)
 	(delete-region part-beg part-end)
 	(apply #'notmuch-show-insert-bodypart-internal part-args)
-	(indent-rigidly part-beg
+	(notmuch--indent-rigidly part-beg
 			part-end
 			(* notmuch-show-indent-messages-width depth)))
       (goto-char part-end)
@@ -1095,7 +1114,7 @@ is t, hide the part initially and show the button."
     (setq content-end (point-marker))
     ;; Indent according to the depth in the thread.
     (when notmuch-show-indent-content
-      (indent-rigidly content-start
+      (notmuch--indent-rigidly content-start
 		      content-end
 		      (* notmuch-show-indent-messages-width depth)))
     (setq message-end (point-max-marker))
-- 
2.33.0