Subject: bug#21777: 25.0.50; gud-gdb uses a pager, which is harmful inside emacs

From: Lars Ingebrigtsen <[email-masked]>
Date: Sun, 20 Sep 2020 23:18:32 +0200

Eli Zaretskii <[email-masked]> writes:

> IME, users sometimes have some use cases that look really weird to me,
> but are somehow very important to them.  So I'm trying to avoid
> stepping on their toes as much as possible, even if I cannot imagine
> those use cases in advance.

I worked up a patch for this, but in testing, there's a number of
problems.

1) When resizing a frame, the height in gdb is overwritten.  Where does
that come from?  I tried grepping, but couldn't find anything.

2) Sending a command this way to gdb gives us an extra prompt, which
isn't nice.

3) If you start gdb with M-x gdb instead of M-x gud-gdb, the height
variable in gdb is always switched off:

  (gdb-input "-gdb-set height 0" 'ignore)

So why shouldn't gud-gdb do the same thing?

diff --git a/doc/emacs/building.texi b/doc/emacs/building.texi
index 7074bd45d7..ac54c570cd 100644
--- a/doc/emacs/building.texi
+++ b/doc/emacs/building.texi
@@ -1040,6 +1040,15 @@ GDB User Interface Layout
 need to check that the breakpoints in recently edited source files are
 still in the right places.
 
+@vindex gud-pager-height
+  GDB normally uses a pager when displaying output (like backtraces).
+This can be inconvenient when running inside Emacs, so the default
+value of @code{gud-pager-height} is @code{unlimited}, meaning that the
+pager is disabled.  This variable can also be a number (which is used
+as the number of lines by the pager), or @code{nil}, meaning that the
+pager setting shouldn't be changed from the gdb defaults (or
+@file{.gdbinit} settings).
+
 @node Source Buffers
 @subsubsection Source Buffers
 @cindex fringes, for debugging
diff --git a/etc/NEWS b/etc/NEWS
index 1f52341ae4..3014eddbdd 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1034,6 +1034,10 @@ window after starting).  This variable defaults to nil.
 
 ** Miscellaneous
 
+*** New user option 'gud-pager-height'
+This variable is used to set up the gdb pager, and defaults to
+`unlimited', meaning that a pager won't be used.
+
 +++
 *** Interactive regular expression search now uses faces for sub-groups.
 E.g., 'C-M-s foo-\([0-9]+\)' will now use the 'isearch-group-1' face
diff --git a/lisp/progmodes/gud.el b/lisp/progmodes/gud.el
index 84c473ddb7..7acc540b01 100644
--- a/lisp/progmodes/gud.el
+++ b/lisp/progmodes/gud.el
@@ -67,6 +67,19 @@ gud-key-prefix
   :type 'key-sequence
   :group 'gud)
 
+(defcustom gud-pager-height 'unlimited
+  "The size of a page when gdb displays output.
+gdb normally uses a pager when displaying things like
+backtraces (or other things that take a lot of room).  This
+variable allows customizing the pager when gdb is run from Emacs.
+
+This can be a number (the number of lines), `unlimited' (don't
+use the pager at all), or nil (don't change the defaults)."
+  :type '(choice (const :tag "No paging" unlimited)
+                 integer
+                 (const :tag "Don't set" nil))
+  :version "28.1")
+
 (global-set-key (vconcat gud-key-prefix "\C-l") 'gud-refresh)
 ;; (define-key ctl-x-map " " 'gud-break); backward compatibility hack
 
@@ -796,6 +809,9 @@ gud-gdb
   (setq gdb-first-prompt t)
   (setq gud-running nil)
   (setq gud-filter-pending-text nil)
+
+  (when gud-pager-height
+    (gud-basic-call (format "set height %s" gud-pager-height)))
   (run-hooks 'gud-gdb-mode-hook))
 
 ;; The completion process filter indicates when it is finished.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no