vim-patch:9.1.0406: Divide by zero with getmousepos() and 'smoothscroll' (#28701)

Problem:  Divide by zero with getmousepos() and 'smoothscroll'.
Solution: Don't compute skip_lines when width1 is zero.
          (zeertzjq)

closes: vim/vim#14747

https://github.com/vim/vim/commit/031a745608d615d56f9d79bb0f76e2a74b2eaf14

3 files changed, 84 insertions, 10 deletions

diff --git a/src/nvim/mouse.c b/src/nvim/mouse.c
index 9d30d7d5ab..f393b0fd0f 100644
--- a/src/nvim/mouse.c
+++ b/src/nvim/mouse.c
@@ -1621,16 +1621,21 @@ bool mouse_comp_pos(win_T *win, int *rowp, int *colp, linenr_T *lnump)
     }
 
     if (win->w_skipcol > 0 && lnum == win->w_topline) {
-      // Adjust for 'smoothscroll' clipping the top screen lines.
-      // A similar formula is used in curs_columns().
       int width1 = win->w_width_inner - win_col_off(win);
-      int skip_lines = 0;
-      if (win->w_skipcol > width1) {
-        skip_lines = (win->w_skipcol - width1) / (width1 + win_col_off2(win)) + 1;
-      } else if (win->w_skipcol > 0) {
-        skip_lines = 1;
+
+      if (width1 > 0) {
+        int skip_lines = 0;
+
+        // Adjust for 'smoothscroll' clipping the top screen lines.
+        // A similar formula is used in curs_columns().
+        if (win->w_skipcol > width1) {
+          skip_lines = (win->w_skipcol - width1) / (width1 + win_col_off2(win)) + 1;
+        } else if (win->w_skipcol > 0) {
+          skip_lines = 1;
+        }
+
+        count -= skip_lines;
       }
-      count -= skip_lines;
     }
 
     if (count > row) {
diff --git a/src/nvim/move.c b/src/nvim/move.c
index 078ce3d72c..66667cecc4 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -1974,11 +1974,13 @@ void scroll_cursor_bot(win_T *wp, int min_scroll, bool set_topbot)
       // need to scroll the additional clipped lines to scroll past the
       // top line before we can move on to the other lines.
       int top_plines = plines_win_nofill(wp, wp->w_topline, false);
-      int skip_lines = 0;
       int width1 = wp->w_width_inner - win_col_off(wp);
+
       if (width1 > 0) {
         int width2 = width1 + win_col_off2(wp);
-        // similar formula is used in curs_columns()
+        int skip_lines = 0;
+
+        // A similar formula is used in curs_columns().
         if (wp->w_skipcol > width1) {
           skip_lines += (wp->w_skipcol - width1) / width2 + 1;
         } else if (wp->w_skipcol > 0) {
diff --git a/test/old/testdir/test_functions.vim b/test/old/testdir/test_functions.vim
index ea0e3790cc..7c712818f9 100644
--- a/test/old/testdir/test_functions.vim
+++ b/test/old/testdir/test_functions.vim
@@ -3399,6 +3399,73 @@ func Test_getmousepos()
         \ column: 8,
         \ coladd: 21,
         \ }, getmousepos())
+
+  30vnew
+  setlocal smoothscroll number
+  call setline(1, join(range(100)))
+  exe "normal! \<C-E>"
+  call Ntest_setmouse(1, 5)
+  call assert_equal(#{
+        \ screenrow: 1,
+        \ screencol: 5,
+        \ winid: win_getid(),
+        \ winrow: 1,
+        \ wincol: 5,
+        \ line: 1,
+        \ column: 27,
+        \ coladd: 0,
+        \ }, getmousepos())
+  call Ntest_setmouse(2, 5)
+  call assert_equal(#{
+        \ screenrow: 2,
+        \ screencol: 5,
+        \ winid: win_getid(),
+        \ winrow: 2,
+        \ wincol: 5,
+        \ line: 1,
+        \ column: 53,
+        \ coladd: 0,
+        \ }, getmousepos())
+
+  exe "normal! \<C-E>"
+  call Ntest_setmouse(1, 5)
+  call assert_equal(#{
+        \ screenrow: 1,
+        \ screencol: 5,
+        \ winid: win_getid(),
+        \ winrow: 1,
+        \ wincol: 5,
+        \ line: 1,
+        \ column: 53,
+        \ coladd: 0,
+        \ }, getmousepos())
+  call Ntest_setmouse(2, 5)
+  call assert_equal(#{
+        \ screenrow: 2,
+        \ screencol: 5,
+        \ winid: win_getid(),
+        \ winrow: 2,
+        \ wincol: 5,
+        \ line: 1,
+        \ column: 79,
+        \ coladd: 0,
+        \ }, getmousepos())
+
+  vert resize 4
+  call Ntest_setmouse(2, 2)
+  " This used to crash Vim
+  call assert_equal(#{
+        \ screenrow: 2,
+        \ screencol: 2,
+        \ winid: win_getid(),
+        \ winrow: 2,
+        \ wincol: 2,
+        \ line: 1,
+        \ column: 53,
+        \ coladd: 0,
+        \ }, getmousepos())
+
+  bwipe!
   bwipe!
 endfunc