[nongnu] elpa/pdf-tools 8e500e509b 1/2: Fix: Handle nil return value from `image-scroll` functions

[ELPA Syncer]

branch: elpa/pdf-tools
commit 8e500e509ba20a6f1e2f794211055893774cbdaf
Author: Vedang Manerikar <ved.manerikar@gmail.com>
Commit: Vedang Manerikar <ved.manerikar@gmail.com>

    Fix: Handle nil return value from `image-scroll` functions
    
    *Note*: This is a temporary fix.
    
    What happened?
    
    When the `arg` to `image-scroll-up` is 0, the function disregards the
    argument (scrolling up 0 lines means not changing anything) and
    returns a `nil` value. This causes the equality check in this commit
    to fail (the check is to see if we have hit the top or bottom of the
    page, since in this case "moving the image" will do nothing and we
    will have to move the page).
    
    The current fix adds an explicit null check to ensure that we don't
    compare scroll positions.
    
    Unknowns: under what conditions is the argument to
    `pdf-view-scroll-up-or-next-page` 0?
    
    Things to do: Review the `= window-vscroll image-scroll` pattern all
    over the code-base and refactor it to deal with `arg = 0` problem.
    
    Fixes: #131
---
 lisp/pdf-view.el | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/lisp/pdf-view.el b/lisp/pdf-view.el
index 7f7e57d52a..0820e8f3e4 100644
--- a/lisp/pdf-view.el
+++ b/lisp/pdf-view.el
@@ -705,12 +705,15 @@ next page only on typing SPC (ARG is nil)."
   (interactive "P")
   (if (or pdf-view-continuous (null arg))
       (let ((hscroll (window-hscroll))
-            (cur-page (pdf-view-current-page)))
-        (when (or (= (window-vscroll nil 
pdf-view-have-image-mode-pixel-vscroll)
-                     (image-scroll-up arg))
-                  ;; Workaround rounding/off-by-one issues.
-                  (memq pdf-view-display-size
-                        '(fit-height fit-page)))
+            (cur-page (pdf-view-current-page))
+            (win-scroll (window-vscroll nil 
pdf-view-have-image-mode-pixel-vscroll))
+            (img-scroll (image-scroll-up arg)))
+        (when (or
+               ;; There is no next line for the image to scroll to
+               (and img-scroll (= win-scroll img-scroll))
+               ;; Workaround rounding/off-by-one issues.
+               (memq pdf-view-display-size
+                     '(fit-height fit-page)))
           (pdf-view-next-page)
           (when (/= cur-page (pdf-view-current-page))
             (image-bob)
@@ -727,12 +730,15 @@ to previous page only on typing DEL (ARG is nil)."
   (interactive "P")
   (if (or pdf-view-continuous (null arg))
       (let ((hscroll (window-hscroll))
-            (cur-page (pdf-view-current-page)))
-        (when (or (= (window-vscroll nil 
pdf-view-have-image-mode-pixel-vscroll)
-                     (image-scroll-down arg))
-                  ;; Workaround rounding/off-by-one issues.
-                  (memq pdf-view-display-size
-                        '(fit-height fit-page)))
+            (cur-page (pdf-view-current-page))
+            (win-scroll (window-vscroll nil 
pdf-view-have-image-mode-pixel-vscroll))
+            (img-scroll (image-scroll-down arg)))
+        (when (or
+               ;; There is no previous line for the image to scroll to
+               (and img-scroll (= win-scroll img-scroll))
+               ;; Workaround rounding/off-by-one issues.
+               (memq pdf-view-display-size
+                     '(fit-height fit-page)))
           (pdf-view-previous-page)
           (when (/= cur-page (pdf-view-current-page))
             (image-eob)