New functions to switch back and forth to another major mode

* subr.el (major-mode--suspended): New var.
(major-mode-suspend, major-mode-restore): New funs, extracted from doc-view.
* doc-view.el (doc-view--previous-major-mode): Remove.
(doc-view-mode): Use major-mode-suspend.
(doc-view-fallback-mode): Use major-mode-restore.
* hexl-mode.el (hexl-mode--minor-mode-p, hexl-mode--setq-local): Remove.
(hexl-mode): Use major-mode-suspend and hexl-follow-ascii-mode.
(hexl-mode-exit): Use major-mode-restore.
(hexl-activate-ruler, hexl-follow-line): Don't bother trying to preserve
earlier state, now that entering/leaving hexl-mode kills local vars.
(hexl-follow-ascii-mode): New proper local minor mode.
(hexl-follow-ascii): Rewrite, using it.
* image-mode.el (image-mode-previous-major-mode): Remove.
(image-mode): Use major-mode-suspend.
(image-mode-to-text): Use major-mode-restore.

1 files changed, 4 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 537e99c90e8..83e106ced8c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -658,6 +658,10 @@ manual for more details.
 
 * Lisp Changes in Emacs 27.1
 
+** New functions 'major-mode-suspend' and 'major-mode-restore'
+Used when switching temporarily to another major mode, e.g. for hexl-mode,
+or to switch between c-mode and image-mode in XPM.
+
 +++
 ** New macro 'dolist-with-progress-reporter'.
 This works like 'dolist', but reports progress similar to