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.

1 files changed, 3 insertions, 0 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 @@ The indicator type which Flymake should use to indicate lines with
 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