[Fontconfig] complicated ordering

[Akira TAGOH]

Hi,

fontconfig will read the xml files according to the alphanumerical
ordering. one may expects that the earlier one would have a priority
than later one. actually this is true for "prepend", "assign_replace"
and "append_last" too in some cases. but not for "prepend_first",
"assign" and "append" due to its behavior. though "prepend_first" may
be an exception here, because it's a bit special case to use. also I
believe we are relying on this to apply the user configuration
effectively.

Anyway this may be one of reasons why it causes confusion and mess up
the config directory. so why does this happen? see:

<match>
  <test name="family"><string>blahblahblah</string></test>
  <edit name="family" mode="append">
    <string>A</string>
    <string>B</string>
    <string>C</string>
  </edit>
</match>

This is a typical rule as known as what <accept> does. this ensure the
order of A/B/C fonts as substitute of blahblahblah there though,
similar rules reading later will overrides it. see:

Substitute match
        pattern any family Equal(ignore blanks) "blahblahblah"
edit
        Edit family Append "A" Comma "B" Comma "C";

Append list before  "blahblahblah"(s) [insert here]
Append list after  "blahblahblah"(s) "A"(s) "B"(s) "C"(s)
...
Substitute match
        pattern any family Equal(ignore blanks) "blahblahblah"
edit
        Edit family Append "D";

Append list before  "blahblahblah"(s) [insert here] "A"(s) "B"(s) "C"(s)
Append list after  "blahblahblah"(s) "D"(s) "A"(s) "B"(s) "C"(s)

Which isn't expected behavior according to the above prioritization.
FWIW "append_last" doesn't work in some cases, particularly when other
rules takes effect to the list prior to the above last one.

Well, I'm wondering if we may need to change the data structure to
group according to the edit mode or so for long term solution. for
short term solution, the above case can be improved with the sort of
"hook" as the following. e.g. 30-metrics-alias.conf to:

30-0-metrics-alias.conf:
<match>
  <test name="family"><string>Arial</string></test>
  <edit name="family" mode="append" binding="same">
    <string>metrics-alias-Arial</string>
  </edit>
</match>

30-1-metrics-alias-arial.conf:
<match>
  <test name="family"><string>metrics-alias-Arial</string></test>
  <edit name="family" mode="prepend" binding="same">
    <string>Liberation Sans</string>
  </edit>
</match>

30-2-metrics-alias-arial.conf:
<match>
  <test name="family"><string>metrics-alias-Arial</string></test>
  <edit name="family" mode="prepend" binding="same">
    <string>Albany</string>
  </edit>
</match>

30-999-metrics-alias-arial.conf:
<!-- better cleanup perhaps? though it prevents to put similar rules
later and this enforces to have "30-n" numeric prefix then -->
<match>
  <test name="family"><string>metrics-alias-Arial</string></test>
  <edit name="family" mode="delete" />
</match>

After this, no need to put rules prior to 30-metrics-alias.conf any
more. and it would looks clearer what kind of rules is in the config
directory. though there are still no way to do "assign"ing with the
same prioritization.

How does it look like?
Any feedback, comments or counterparts are welcome.

Regards,
-- 
Akira TAGOH