Prepare for Unicode 9.0

The major code changes needed to support Unicode 9.0 are to changes in
the boundary (break) rules, for things like \b{lb}, \b{wb}.
regen/mk_invlists.pl creates two-dimensional arrays for all these
properties.  To see if a given point in the target string is a break or
not, regexec.c looks up the entry in the property's table whose row
corresponds to the code point before the potential break, and whose
column corresponds to the one after.  Mostly this is completely
determining, but for some cases, extra context is required, and the
array entry indicates this, and there has to be specially crafted code
in regexec.c to handle each such possibility.  When a new release comes
along, mk_invlists.pl has to be changed to handle any new or changed
rules, and regexec.c has to be changed to handle any changes to the
custom code.

Unfortunately this is not a mature area of the Standard, and changes are
fairly common in new releases.  In part, this is because new types of
code points come along, which need new rules.  Sometimes it is because
they realized the previous version didn't work as well as it could.  An
example of the latter is that Unicode now realizes that Regional
Indicator (RI) characters come in pairs, and that one should be able to
break between each pair, but not within a pair.  Previous versions
treated any run of them as unbreakable.  (Regional Indicators are a
fairly recent type that was added to the Standard in 6.0, and things are
still getting shaken out.)

The other main changes to these rules also involve a fairly new type of
character, emojis.  We can expect further changes to these in the next
Unicode releases.

\b{gcb} for the first time, now depends on context (in rarely
encountered cases, like RI's), so the function had to be changed from a
simple table look-up to be more like the functions handling the other
break properties.

Some years ago I revamped mktables in part to try to make it require as
few manual interventions as possible when upgrading to a new version of
Unicode.  For example, a new data file in a release requires telling
mktables about it, but as long as it follows the format of existing
recent files, nothing else need be done to get whatever properties it
describes to be included.

Some of changes to mktables involved guessing, from existing limited
data, what the underlying paradigm for that data was.  The problem with
that is there may not have been a paradigm, just something they did ad
hoc, which can change at will; or I didn't understand their unstated
thinking, and guessed wrong.

Besides the boundary rule changes, the only change that the existing
mktables couldn't cope with was the addition of the Tangut script, whose
character names include the code point, like CJK UNIFIED IDEOGRAPH-3400
has always done.  The paradigm for this wasn't clear, since CJK was the
only script that had this characteristic, and so I hard-coded it into
mktables.  The way Tangut is structured may show that there is a
paradigm emerging (but we only have two examples, and there may not be a
paradigm at all), and so I have guessed one, and changed mktables to
assume this guessed paradigm.  If other scripts like this come along,
and I have guessed correctly, mktables will cope with these
automatically without manual intervention.

1 files changed, 2 insertions, 1 deletions

diff --git a/embed.h b/embed.h
index f37b76b90c..f32f31733d 100644
--- a/embed.h
+++ b/embed.h
@@ -1111,13 +1111,14 @@
 #define advance_one_LB(a,b,c)	S_advance_one_LB(aTHX_ a,b,c)
 #define advance_one_SB(a,b,c)	S_advance_one_SB(aTHX_ a,b,c)
 #define advance_one_WB(a,b,c,d)	S_advance_one_WB(aTHX_ a,b,c,d)
+#define backup_one_GCB(a,b,c)	S_backup_one_GCB(aTHX_ a,b,c)
 #define backup_one_LB(a,b,c)	S_backup_one_LB(aTHX_ a,b,c)
 #define backup_one_SB(a,b,c)	S_backup_one_SB(aTHX_ a,b,c)
 #define backup_one_WB(a,b,c,d)	S_backup_one_WB(aTHX_ a,b,c,d)
 #define find_byclass(a,b,c,d,e)	S_find_byclass(aTHX_ a,b,c,d,e)
 #define isFOO_lc(a,b)		S_isFOO_lc(aTHX_ a,b)
 #define isFOO_utf8_lc(a,b)	S_isFOO_utf8_lc(aTHX_ a,b)
-#define isGCB			S_isGCB
+#define isGCB(a,b,c,d,e)	S_isGCB(aTHX_ a,b,c,d,e)
 #define isLB(a,b,c,d,e,f)	S_isLB(aTHX_ a,b,c,d,e,f)
 #define isSB(a,b,c,d,e,f)	S_isSB(aTHX_ a,b,c,d,e,f)
 #define isWB(a,b,c,d,e,f,g)	S_isWB(aTHX_ a,b,c,d,e,f,g)