patch 9.0.1561: display wrong when moving cursor to above the top line

Problem:    Display wrong when moving cursor to above the top line and
            'smoothscroll' is set.
Solution:   Call adjust_skipcol() in more places and make it work better.
            (Luuk van Baal, closes #12395)

src/move.c

@@ -1960,12 +1960,14 @@ adjust_skipcol(void)
 	    curwin->w_skipcol -= width2;
 	else
 	    curwin->w_skipcol -= width1;
-	redraw_later(UPD_NOT_VALID);
 	scrolled = TRUE;
-	validate_virtcol();
     }
     if (scrolled)
+    {
+	validate_virtcol();
+	redraw_later(UPD_NOT_VALID);
 	return;  // don't scroll in the other direction now
+    }
 
     int col = curwin->w_virtcol - curwin->w_skipcol + scrolloff_cols;
     int row = 0;

src/testdir/dumps/Test_display_cursor_long_line.dump

@@ -1,8 +0,0 @@
-|<+0#4040ff13#ffffff0@2|b+0#0000000&@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| 
-|b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@2
-@2| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| 
-|b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@2
-@2| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| 
-|b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@2
-@2| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4| |b@4> 
-@57|2|,|6|0@1| @8|5|0|%| 

src/testdir/dumps/Test_display_cursor_long_line_1.dump

@@ -0,0 +1,8 @@
+|<+0#4040ff13#ffffff0@2|b+0#0000000&@71
+@75
+@75
+@75
+@75
+@75
+@1>b| @72
+@57|2|,|7|5|2| @8|5|0|%| 

src/testdir/dumps/Test_display_cursor_long_line_2.dump

@@ -0,0 +1,8 @@
+|<+0#4040ff13#ffffff0@2|b+0#0000000&>b@70
+@75
+@75
+@75
+@75
+@75
+@75
+| @56|2|,|1| @10|5|0|%| 

src/testdir/dumps/Test_display_cursor_long_line_3.dump

@@ -0,0 +1,8 @@
+| +0#af5f00255#ffffff0@1|2| |b+0#0000000&| >b@68
+@75
+@75
+@75
+@75
+@75
+@75
+| @56|2|,|3| @10|5|0|%| 

src/testdir/dumps/Test_display_cursor_long_line_4.dump

@@ -0,0 +1,8 @@
+| +0#af5f00255#ffffff0@1|2| >b+0#0000000&| |b@68
+@75
+@75
+@75
+@75
+@75
+@75
+| @56|2|,|1| @10|5|0|%| 

src/testdir/test_display.vim

@@ -507,14 +507,29 @@ func Test_display_cursor_long_line()
   CheckScreendump
 
   let lines =<< trim END
-    call setline(1, ['a', 'bbbbb '->repeat(100), 'c'])
+    call setline(1, ['a', 'b ' .. 'bbbbb'->repeat(150), 'c'])
     norm $j
   END
 
   call writefile(lines, 'XdispCursorLongline', 'D')
   let buf = RunVimInTerminal('-S XdispCursorLongline', #{rows: 8})
 
-  call VerifyScreenDump(buf, 'Test_display_cursor_long_line', {})
+  call VerifyScreenDump(buf, 'Test_display_cursor_long_line_1', {})
+
+  " FIXME: moving the cursor above the topline does not set w_skipcol
+  " correctly with cpo+=n and zero scrolloff (curs_columns() extra == 1).
+  call term_sendkeys(buf, ":set number cpo+=n scrolloff=0\<CR>")
+  call term_sendkeys(buf, '$0')
+  call VerifyScreenDump(buf, 'Test_display_cursor_long_line_2', {})
+
+  " Going to the start of the line with "b" did not set w_skipcol correctly
+  " with 'smoothscroll'.
+   call term_sendkeys(buf, ":set smoothscroll\<CR>")
+   call term_sendkeys(buf, '$b')
+   call VerifyScreenDump(buf, 'Test_display_cursor_long_line_3', {})
+  " Same for "ge".
+   call term_sendkeys(buf, '$ge')
+   call VerifyScreenDump(buf, 'Test_display_cursor_long_line_4', {})
 
   call StopVimInTerminal(buf)
 endfunc

src/testdir/test_scroll_opt.vim

@@ -502,7 +502,7 @@ func Test_smoothscroll_cursor_position()
   " regardless of number and cpo-=n.
   setl number list listchars=precedes:< cpo-=n
   call s:check_col_calc(5, 1, 1)
-  exe "normal 2|\<C-E>"
+  exe "normal 3|\<C-E>h"
   call s:check_col_calc(6, 1, 18)
   norm h
   call s:check_col_calc(5, 2, 17)

src/textobject.c

@@ -472,6 +472,7 @@ bck_word(long count, int bigword, int stop)
 finished:
 	stop = FALSE;
     }
+    adjust_skipcol();
     return OK;
 }
 
@@ -598,6 +599,7 @@ bckend_word(
 		return OK;
 	}
     }
+    adjust_skipcol();
     return OK;
 }
 

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1561,
 /**/
     1560,
 /**/