patch 9.1.0787: cursor position changed when using hidden terminal

Problem:  cursor position changed when using hidden terminal
          and BufFilePost autocommand (Mizuno Jan Yuta)
Solution: Save and restore cursor position

fixes: #15854
closes: #15876

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/terminal.c

@@ -446,6 +446,7 @@ term_start(
     buf_T	*newbuf;
     int		vertical = opt->jo_vertical || (cmdmod.cmod_split & WSP_VERT);
     jobopt_T	orig_opt;  // only partly filled
+    pos_T	save_cursor;
 
     if (check_restricted() || check_secure())
 	return NULL;
@@ -518,6 +519,7 @@ term_start(
 	old_curbuf = curbuf;
 	--curbuf->b_nwindows;
 	curbuf = buf;
+	save_cursor = curwin->w_cursor;
 	curwin->w_buffer = buf;
 	++curbuf->b_nwindows;
     }
@@ -763,6 +765,7 @@ term_start(
 	    --curbuf->b_nwindows;
 	    curbuf = old_curbuf;
 	    curwin->w_buffer = curbuf;
+	    curwin->w_cursor = save_cursor;
 	    ++curbuf->b_nwindows;
 	}
 	else if (vgetc_busy

src/testdir/test_terminal3.vim

@@ -975,4 +975,29 @@ func Test_terminal_vertical()
   call v9.CheckLegacyAndVim9Success(lines)
 endfunc
 
+" Needs to come before Test_hidden_terminal(), why?
+func Test_autocmd_buffilepost_with_hidden_term()
+  CheckExecutable true
+  new XTestFile
+  defer delete('XTestFile')
+  call setline(1, ['one', 'two', 'three'])
+  call cursor(3, 10)
+  augroup TestCursor
+    au!
+    autocmd BufFilePost * call setbufvar(3, '&tabstop', 4)
+  augroup END
+
+  let buf = term_start(['true'], #{hidden: 1, term_finish: 'close'})
+  call term_wait(buf)
+  redraw!
+  call assert_equal('XTestFile', bufname('%'))
+  call assert_equal([0, 3, 5, 0], getpos('.'))
+
+  augroup TestCursor
+    au!
+  augroup END
+  augroup! TestCursor
+  bw! XTestFile
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    787,
 /**/
     786,
 /**/