Subject: Re: bug#77313: 30.1.50; Regression: flymake indicators are erroneously using margins

From: Spencer Baugh <[email-masked]>
Date: Tue, 08 Apr 2025 17:50:38 -0400

Eli Zaretskii <[email-masked]> writes:
>> From: Spencer Baugh <[email-masked]>
>> Date: Tue, 8 Apr 2025 08:43:37 -0400
>> Subject: [PATCH] flymake: fall back to margins on text terminals
>> 
>> Previously, flymake-indicator-type defaulted to either fringes
>> or margins.  But fringes should be used on graphical frames, and
>> margins on TTY frames.  So default to fringes instead, and
>> simply fall back to margins automatically on text frames.
>
> The above needs to be updated to mention the disabled fringes.

Updated.

>> * lisp/progmodes/flymake.el (flymake-indicator-type): Set to
>> fringes.  (bug#77313)
>> (flymake-mode): Fallback to margins if there's no fringes.
>
> This needs a NEWS entry, but other than that it LGTM.  Let's wait for
> a couple of days to let others a chance to comment.

Added a NEWS entry.

>From 792d90c4f01a6b054a4a05ae7dc2598716def7ea Mon Sep 17 00:00:00 2001
From: Spencer Baugh <[email-masked]>
Date: Tue, 8 Apr 2025 08:43:37 -0400
Subject: [PATCH] flymake: fall back to margins on text terminals

Previously, flymake-indicator-type defaulted to either fringes
or margins.  But fringes should be used on graphical frames, and
margins on TTY frames.  So default to fringes instead, and
simply fall back to margins automatically on text frames.

* lisp/progmodes/flymake.el (flymake-indicator-type): Set to
fringes.  (bug#77313)
(flymake-mode): Fallback to margins if there's no fringes.
* doc/misc/flymake.texi (Customizable variables): Mention
fallback behavior.
* etc/NEWS: Announce fallback behavior.
---
 doc/misc/flymake.texi     |  3 +++
 etc/NEWS                  |  8 ++++++++
 lisp/progmodes/flymake.el | 20 ++++++++++++++------
 3 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/doc/misc/flymake.texi b/doc/misc/flymake.texi
index 54835767928..668a72b4cd1 100644
--- a/doc/misc/flymake.texi
+++ b/doc/misc/flymake.texi
@@ -313,6 +313,9 @@ Customizable variables
 errors or warnings.
 Depending on your preference, this can either use @code{fringes} or
 @code{margins} for indicating errors.
+If set to @code{fringes} (the default), it will automatically fall back
+to using margins in windows or frames without fringes, such as text
+terminals.
 
 @item flymake-error-bitmap
 A bitmap used in the fringe to mark lines for which an error has
diff --git a/etc/NEWS b/etc/NEWS
index b2286236d57..123a04527c4 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1720,6 +1720,14 @@ change their face if the current line exceeds the 'fill-column'.  The
 new face 'display-fill-column-indicator-warning-face' is used to
 highlight the fill-column indicators.  By default this is disabled.
 
+---
+** Flymake
+
+*** Windows without fringes now automatically use margin indicators
+When flymake-indicator-type is set to 'fringes', as is now the default,
+flymake will automatically fall back to using margin indicators in
+windows without fringes, including any window in a text terminal.
+
 
 * New Modes and Packages in Emacs 31.1
 
diff --git a/lisp/progmodes/flymake.el b/lisp/progmodes/flymake.el
index 6cc7e1f7a79..7340fed9be4 100644
--- a/lisp/progmodes/flymake.el
+++ b/lisp/progmodes/flymake.el
@@ -185,22 +185,23 @@ flymake-fringe-indicator-position
 		 (const right-fringe)
 		 (const :tag "No fringe indicators" nil)))
 
-(defcustom flymake-indicator-type (if (display-graphic-p)
-                                      'fringes
-                                    'margins)
+(defcustom flymake-indicator-type 'fringes
   "Indicate which indicator type to use for display errors.
 
 The value can be nil (don't indicate errors but just highlight them),
-fringes (use fringes) or margins (use margins)
+the symbol `fringes' (use fringes) or the symbol `margins' (use
+margins).
 
 Difference between fringes and margin is that fringes support displaying
 bitmaps on graphical displays and margins display text in a blank area
 from current buffer that works in both graphical and text displays.
+Thus, even when `fringes' is selected, margins will still be used on
+text displays and also when fringes are disabled.
 
 See Info node `Fringes' and Info node `(elisp)Display Margins'."
-  :version "30.1"
+  :version "31.1"
   :type '(choice (const :tag "Use Fringes" fringes)
-                 (const :tag "Use Margins "margins)
+                 (const :tag "Use Margins" margins)
                  (const :tag "No indicators" nil)))
 
 (defcustom flymake-margin-indicators-string
@@ -1439,6 +1440,13 @@ flymake-mode
     (add-hook 'kill-buffer-hook 'flymake-kill-buffer-hook nil t)
     (add-hook 'eldoc-documentation-functions 'flymake-eldoc-function t t)
 
+    (when (and (eq flymake-indicator-type 'fringes)
+               (not (cl-case flymake-fringe-indicator-position
+                      (left-fringe (< 0 (nth 0 (window-fringes))))
+                      (right-fringe (< 0 (nth 1 (window-fringes)))))))
+      ;; There are no fringes in the buffer, fallback to margins.
+      (setq-local flymake-indicator-type 'margins))
+
     ;; AutoResize margins.
     (flymake--resize-margins)
 
-- 
2.39.3