bug#1952: 23.0.60[W32-Mingw]; opening etc/HELLO is slower than before

[Jason Rumney <jasonr@gnu.org>]

Juanma Barranquero wrote:
> I think Kevin Yu is right. Moving around in etc/HELLO, even with a lot
> of installed fonts, was quite fast until this change:
>
> 2009-01-09  Jason Rumney  <jasonr@gnu.org>
>
>         * w32font.c (add_font_entity_to_list): Don't report unknown
>         Windows charset as any unrecognized registry.  (Bug#1548)
>         Only report Unicode Plane 2 fonts as unicode-sip.
>
> Now, moving in etc/HELLO is unbearably slow. I'm talking of typing
> <down> and waiting about two seconds for the cursor to move.
>   

I don't see any slowness when scrolling, but it may be because I do not 
have a lot of fonts installed compared with some people, or it may be 
because I have fonts installed for all the languages in HELLO, so there 
are no failures (which I suspect may not get cached).

One of the changes made at the same time as the above (which I 
apparently forgot to add a ChangeLog entry for) was to fix the return 
value of add_one_font_entity_to_list. This function was supposed to 
abort the font enumeration as soon as a match was found. But previously 
the logic was wrong so it was aborting if the first font did not match 
the given font-spec. So in the majority of cases, it would only 
enumerate one font and return nil, only if the first font matched would 
it go through every font in the system and return all the fonts that 
matched. After the fix, it will go through all the fonts for characters 
that do not have a matching font installed, and will go through enough 
fonts to find a match for others.

Since there was no visible bug previously, I wonder what use this 
function is, and whether it is just wasting time looking for a match 
that we already have.