bug#36832: Supply option to suppress scrolling in compilation mode buffers.

[Alan Mackenzie <acm@muc.de>]

Hello, Emacs.

In a compilation mode buffer, hit CR on one of the error lines so as to
go to the pertinent line in the erroneous source code.

WHAM!  The compilation mode buffer is unavoidably scrolled so that the
line CR'd upon is at the top of the window.  Well, it's unavoidable
unless you're running under a GUI and have fringes enabled.

This forced scrolling is irritating for at least one Emacs developer.

I propose enhancing the customisation variable compilation-context-lines
with the extra value t meaning "never scroll the compilation mode buffer".

Here is a patch to achieve this:



diff --git a/lisp/progmodes/compile.el b/lisp/progmodes/compile.el
index 4b2fc516c3..5a8680fd0c 100644
--- a/lisp/progmodes/compile.el
+++ b/lisp/progmodes/compile.el
@@ -2546,26 +2546,30 @@ compilation-context-lines
   "Display this many lines of leading context before the current message.
 If nil and the left fringe is displayed, don't scroll the
 compilation output window; an arrow in the left fringe points to
-the current message.  If nil and there is no left fringe, the message
-displays at the top of the window; there is no arrow."
-  :type '(choice integer (const :tag "No window scrolling" nil))
+the current message.  If nil and there is no left fringe, the
+message displays at the top of the window; there is no arrow.  If
+t, don't scroll the compilation output window at all."
+  :type '(choice integer
+                 (const :tag "Scroll window when no fringe" nil)
+                 (const :tag  "No window scrolling" t))
   :version "22.1")
 
 (defsubst compilation-set-window (w mk)
-  "Align the compilation output window W with marker MK near top."
-  (if (integerp compilation-context-lines)
-      (set-window-start w (save-excursion
-			    (goto-char mk)
-			    (compilation-beginning-of-line
-			     (- 1 compilation-context-lines))
-			    (point)))
+  "Maybe align the compilation output window W with marker MK near top."
+  (cond ((integerp compilation-context-lines)
+         (set-window-start w (save-excursion
+			       (goto-char mk)
+			       (compilation-beginning-of-line
+			        (- 1 compilation-context-lines))
+			       (point))))
+        ((eq compilation-context-lines t))
     ;; If there is no left fringe.
-    (when (equal (car (window-fringes w)) 0)
-      (set-window-start w (save-excursion
-                            (goto-char mk)
-			    (beginning-of-line 1)
-			    (point)))))
-    (set-window-point w mk))
+        ((equal (car (window-fringes w)) 0)
+         (set-window-start w (save-excursion
+                               (goto-char mk)
+			       (beginning-of-line 1)
+			       (point)))
+         (set-window-point w mk))))
 
 (defvar next-error-highlight-timer)
 

-- 
Alan Mackenzie (Nuremberg, Germany).