Why does this function "skip" on line 63? - function

Question

I am trying to modify this terrific VIM script however both the original and my modified version have a maddening bug in which sometimes the cursor is shown in the wrong place. The simplest example that I could make is the 71 line text file below. Note that whitespace is important when copying the file.
<?php
/**
* Some silly method
*
* #param string Some silly string
*/
function someFunction()
{
global $class, $cv, $go, $pae;
global $messages, $counters, $ltn;
global $sh, $sub, $temp;
$charsets = array(
'us',
'si',
'pr',
'op',
'co',
'pa',
'av',
'pr',
'al',
'pc',
'pe',
'pi',
'pp',
'su',
'qu',
'de',
'ze',
'xo',
'mo',
'wo',
'de',
'mo',
'de',
'mo',
'dr',
'mo',
'de',
'mo',
'ev',
'pa',
'so',
'ms',
'bu',
'at',
'cu',
'pr',
'de',
'mo',
'nv',
'nl',
'nf',
'ne',
'nq',
'nt'
);
}
This is the relevant .vimrc file with the function:
set cul
hi CursorLine term=none cterm=none ctermbg=20
set nu
set statusline+=%{WhatFunctionAreWeIn()}
set laststatus=2
fun WhatFunctionAreWeIn()
let strList = ["while", "foreach", "ifelse", "if else", "for", "if", "else", "try", "catch", "case"]
let foundcontrol = 1
let position = ""
normal mz
while (foundcontrol)
let foundcontrol = 0
" The idea here is to go back to non-whitespace character before
" the last hanging open { and to check if it is a close paran.
" If so, then go to the matching open paren and search for the
" preceding it.
" If not, then go ahead and check the keyword right there.
normal [{
?\S
let tempchar = getline(".")[col(".") - 1]
if (match(tempchar, ")") >=0 )
normal %
?\S
endif
let tempstring = getline(".")
for item in strList
if( match(tempstring,item) >= 0 )
let position = item . " - " . position
let foundcontrol = 1
break
endif
endfor
if(foundcontrol == 0)
normal `z
return tempstring.position
endif
endwhile
normal `z
return tempstring.position
endfun
Starting from the beginning of the file, press j repeatedly until you get to line 63. Note that the highlighted cursorline stays on the correct line (63) but the cursor is shown on line 55. Jumping directly to line 63 won't trigger the bug, only pressing j repeatedly until you get to that line will.
Why does that happen, and how can I fix it? Note that when the cursor appears to be in the wrong place, pressing ``z` does in fact snap the cursor to the correct location. This is on VIM 7.3.154 on Kubuntu 11.10.
EDIT:
I notice by testing in other installs (Debian, CentOS) that the bug is not determinate, it happens occasionally but not in the same place on every system! You can test this code by pressing j and paying attention to the cursor location in whatever PHP files that you might have strung about. I would say that about one line out of every hundred lines triggers the bug in which the cursor appears to be in the wrong place.

Answer 1

I'm slightly confused by the logic of this function, but I suspect it is the ?\S which is causing the problems. It is searching backwards for a non-whitespace character, and wrapping around to the bottom of the file once it has reached the top.
Try replacing both occurrences of ?\S with
call search('\S','bW')
(Here the b flag searches backwards, and W prevents wrapping around the file.)
EDIT (2nd attempt)
The function also causes lots of jumping around of the view. The root of this is continually setting the mark mz and jumping to and fro. A better approach in vimscripts is to use the following commands to save the current view (instead of normal mz):
let pos=getpos(".") " This saves the cursor position
let view=winsaveview() " This saves the window view
You can then use these to restore the view:
call cursor(pos) " This restores the cursor position to that of "pos"
call winrestview(view) " This restores the window view to that of "view"
So I would use call cursor(pos) instead of `z and call winrestview(view) just before the return commands. This ensures that the function doesn't modify the appearance of the window, and makes for more pleasant usage.
Hope this helps!