line() can move the cursor in a zero-height window

Minimal reproduction steps:

1. vim -u NONE -U NONE -i NONE
2. :set winminheight=0
3. :autocmd! WinEnter * echom "ShowLine:" line('w0')
4. :new
5. :setlocal nowrap
6. a1<CR>2<CR>3<Esc>gg
7. <C-W>j<C-_>
8. <C-W>k<C-_>

At this point, I expect the cursor to be on line 1, at the top of the screen.  
Instead, the cursor is on line 3, at the top of the screen.

The bug only manifests when the cursor is on the top line of the window before 
its height is reduced to zero, whether or not that line is the first in the 
file.  The matchparen plugin triggers this bug when the cursor is on a bracket 
within that line.  The cursor always ends up on the last line of the file, 
almost always with that line at the top of the screen.

I primarily use Vim 7.3 on Ubuntu 12.04:

VIM - Vi IMproved 7.3 (2010 Aug 15, compiled May  4 2012 04:22:36)
Included patches: 1-429
Modified by pkg-vim-maintainers@lists.alioth.debian.org
Compiled by buildd@
Huge version with GTK2-GNOME GUI.  Features included (+) or not (-):
+arabic +autocmd +balloon_eval +browse ++builtin_terms +byte_offset +cindent 
+clientserver +clipboard +cmdline_compl +cmdline_hist +cmdline_info +comments 
+conceal +cryptv +cscope +cursorbind +cursorshape
+dialog_con_gui +diff +digraphs +dnd -ebcdic +emacs_tags +eval +ex_extra 
+extra_search +farsi +file_in_path +find_in_path +float +folding -footer 
+fork() +gettext -hangul_input +iconv +insert_expand
+jumplist +keymap +langmap +libcall +linebreak +lispindent +listcmds +localmap 
+lua +menu +mksession +modify_fname +mouse +mouseshape +mouse_dec +mouse_gpm 
-mouse_jsbterm +mouse_netterm -mouse_sysmouse
+mouse_xterm +mouse_urxvt +multi_byte +multi_lang -mzscheme +netbeans_intg 
+path_extra +perl +persistent_undo +postscript +printer +profile +python 
-python3 +quickfix +reltime +rightleft +ruby +scrollbind
+signs +smartindent -sniff +startuptime +statusline -sun_workshop +syntax 
+tag_binary +tag_old_static -tag_any_white +tcl +terminfo +termresponse 
+textobjects +title +toolbar +user_commands +vertsplit
+virtualedit +visual +visualextra +viminfo +vreplace +wildignore +wildmenu 
+windows +writebackup +X11 -xfontset +xim +xsmp_interact +xterm_clipboard 
-xterm_save
Original issue reported on code.google.com by esw...@gmail.com on 25 Aug 2014 at 1:33
odeke-em / vim

line() can move the cursor in a zero-height window #252
