vim-patch:9.0.0911: with 'smoothscroll' set mouse click position may be wrong

Problem:    With 'smoothscroll' set mouse click position may be wrong.
Solution:   Adjust computations for w_skipcol. (Yee Cheng Chin, closes vim/vim#11514)

e6392b1021

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

src/nvim/mouse.c

@@ -1410,9 +1410,22 @@ bool mouse_comp_pos(win_T *win, int *rowp, int *colp, linenr_T *lnump)
       } else {
         row -= win_get_fill(win, lnum);
       }
-      count = plines_win_nofill(win, lnum, true);
+      count = plines_win_nofill(win, lnum, false);
     } else {
-      count = plines_win(win, lnum, true);
+      count = plines_win(win, lnum, false);
+    }
+
+    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 - 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;
+      }
+      count -= skip_lines;
     }
 
     if (count > row) {
@@ -1436,8 +1449,11 @@ bool mouse_comp_pos(win_T *win, int *rowp, int *colp, linenr_T *lnump)
       col = off;
     }
     col += row * (win->w_width_inner - off);
-    // add skip column (for long wrapping line)
+
-    col += win->w_skipcol;
+    // Add skip column for the topline.
+    if (lnum == win->w_topline) {
+      col += win->w_skipcol;
+    }
   }
 
   if (!win->w_p_wrap) {

test/old/testdir/test_scroll_opt.vim

@@ -2,6 +2,7 @@
 
 source check.vim
 source screendump.vim
+source mouse.vim
 
 func Test_reset_scroll()
   let scr = &l:scroll
@@ -469,5 +470,65 @@ func Test_smoothscroll_cursor_position()
   bwipeout!
 endfunc
 
+" Test that mouse picking is still accurate when we have smooth scrolled lines
+func Test_smoothscroll_mouse_pos()
+  CheckNotGui
+  CheckUnix
+
+  let save_mouse = &mouse
+  "let save_term = &term
+  "let save_ttymouse = &ttymouse
+  set mouse=a "term=xterm ttymouse=xterm2
+
+  call NewWindow(10, 20)
+  setl smoothscroll wrap
+  " First line will wrap to 3 physical lines. 2nd/3rd lines are short lines.
+  call setline(1, ["abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", "line 2", "line 3"])
+
+  func s:check_mouse_click(row, col, buf_row, buf_col)
+    call MouseLeftClick(a:row, a:col)
+
+    call assert_equal(a:col, wincol())
+    call assert_equal(a:row, winline())
+    call assert_equal(a:buf_row, line('.'))
+    call assert_equal(a:buf_col, col('.'))
+  endfunc
+
+  " Check that clicking without scroll works first.
+  call s:check_mouse_click(3, 5, 1, 45)
+  call s:check_mouse_click(4, 1, 2, 1)
+  call s:check_mouse_click(4, 6, 2, 6)
+  call s:check_mouse_click(5, 1, 3, 1)
+  call s:check_mouse_click(5, 6, 3, 6)
+
+  " Smooth scroll, and checks that this didn't mess up mouse clicking
+  exe "normal \<C-E>"
+  call s:check_mouse_click(2, 5, 1, 45)
+  call s:check_mouse_click(3, 1, 2, 1)
+  call s:check_mouse_click(3, 6, 2, 6)
+  call s:check_mouse_click(4, 1, 3, 1)
+  call s:check_mouse_click(4, 6, 3, 6)
+
+  exe "normal \<C-E>"
+  call s:check_mouse_click(1, 5, 1, 45)
+  call s:check_mouse_click(2, 1, 2, 1)
+  call s:check_mouse_click(2, 6, 2, 6)
+  call s:check_mouse_click(3, 1, 3, 1)
+  call s:check_mouse_click(3, 6, 3, 6)
+
+  " Make a new first line 11 physical lines tall so it's taller than window
+  " height, to test overflow calculations with really long lines wrapping.
+  normal gg
+  call setline(1, "12345678901234567890"->repeat(11))
+  exe "normal 6\<C-E>"
+  call s:check_mouse_click(5, 1, 1, 201)
+  call s:check_mouse_click(6, 1, 2, 1)
+  call s:check_mouse_click(7, 1, 3, 1)
+
+  let &mouse = save_mouse
+  "let &term = save_term
+  "let &ttymouse = save_ttymouse
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab