>From 0f3a50fa311e6ec1ccb1a0d03d521cc2ef9b309a Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Sun, 28 Aug 2016 17:23:04 -0400
Subject: [PATCH v1 2/3] Don't count mode line for scroll-margin limit

* src/window.c (window_scroll_margin): Subtract mode line height from
upper limit applied to scroll margin (Bug #5718).
* test/src/window-tests.el: New tests for scroll-margin behavior.
---
 src/window.c             |  3 +-
 test/src/window-tests.el | 86 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 test/src/window-tests.el

diff --git a/src/window.c b/src/window.c
index 2046fe7..dbda435 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4800,7 +4800,8 @@ window_scroll_margin (struct window *window, enum margin_unit unit)
     {
       int frame_line_height = default_line_pixel_height (window);
       int window_total_lines
-        = window->total_lines * WINDOW_FRAME_LINE_HEIGHT (window)
+        = (window->total_lines * WINDOW_FRAME_LINE_HEIGHT (window)
+           - WINDOW_MODE_LINE_HEIGHT (window))
         / frame_line_height;
       int margin = min (scroll_margin, window_total_lines / 4);
       if (unit == MARGIN_IN_PIXELS)
diff --git a/test/src/window-tests.el b/test/src/window-tests.el
new file mode 100644
index 0000000..88ded18
--- /dev/null
+++ b/test/src/window-tests.el
@@ -0,0 +1,86 @@
+;;; window-tests.el -- tests for window.c -*- lexical-binding: t -*-
+
+;; Copyright (C) 2016 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert)
+
+(defun window-test-scrolling (margin &optional effective-margin)
+  (unless effective-margin
+    (setq effective-margin margin))
+  (erase-buffer)
+  (insert (mapconcat #'number-to-string
+                     (number-sequence 1 200) "\n"))
+  (goto-char 1)
+  (sit-for 0)
+  (let ((scroll-margin margin)
+        (mode-lines (/ (window-mode-line-height) (line-pixel-height)))
+        (wstart (window-start)))
+    ;; Stopping before `scroll-margin' so we shouldn't have
+    ;; scrolled.
+    (let ((current-prefix-arg (- (window-height)
+                                 mode-lines (window-start) effective-margin)))
+      (call-interactively 'next-line))
+    (sit-for 0)
+    (should (= wstart (window-start)))
+    ;; Passing `scroll-margin' should trigger scrolling.
+    (call-interactively 'next-line)
+    (sit-for 0)
+    (should (/= wstart (window-start)))
+    ;; Scroll back to top.
+    (let ((current-prefix-arg (window-start)))
+      (call-interactively 'scroll-down-command))
+    (sit-for 0)
+    (should (= 1 (window-start)))))
+
+(defmacro window-with-test-buffer-window (&rest body)
+  (let ((bufvar (make-symbol "buf")))
+    `(let ((,bufvar (get-buffer-create "*test*")))
+       (with-selected-window (display-buffer ,bufvar)
+         (with-current-buffer ,bufvar
+           ,@body)))))
+
+(ert-deftest window-test-scroll-margin-0 ()
+  (skip-unless (not noninteractive))
+  (window-with-test-buffer-window
+   (window-test-scrolling 0)))
+
+(ert-deftest window-test-scroll-margin-negative ()
+  "A negative `scroll-margin' should be the same as 0."
+  (skip-unless (not noninteractive))
+  (window-with-test-buffer-window
+   (window-test-scrolling -10 0)))
+
+(ert-deftest window-test-scroll-margin-max ()
+  (skip-unless (not noninteractive))
+  (window-with-test-buffer-window
+   (let* ((mode-lines (/ (window-mode-line-height) (line-pixel-height)))
+          (max-margin (/ (- (window-height) mode-lines) 4)))
+     (window-test-scrolling max-margin))))
+
+(ert-deftest window-test-scroll-margin-over-max ()
+  "A `scroll-margin' more than max should be the same as max."
+  (skip-unless (not noninteractive))
+  (window-with-test-buffer-window
+   ;; Check that mode line is not counted for determining max margin.
+   (set-window-text-height nil 7)
+   (let* ((mode-lines (/ (window-mode-line-height) (line-pixel-height)))
+          (max-margin (/ (- (window-height) mode-lines) 4)))
+     (window-test-scrolling (+ max-margin 1) max-margin)
+     (window-test-scrolling (+ max-margin 2) max-margin))))
-- 
2.9.3