The error code of an allocating function was not checked in tre_add_tag.

this patch makes the functions which work directly on multibyte
characters treat the high bytes as individual abstract code units
rather than as multibyte sequences when MB_CUR_MAX is 1. since
MB_CUR_MAX is presently defined as a constant 4, all of the new code
added is dead code, and optimizing compilers' code generation should
not be affected at all. a future commit will activate the new code.

as abstract code units, bytes 0x80 to 0xff are represented by wchar_t
values 0xdf80 to 0xdfff, at the end of the surrogates range. this
ensures that they will never be misinterpreted as Unicode characters,
and that all wctype functions return false for these "characters"
without needing locale-specific logic. a high range outside of Unicode
such as 0x7fffff80 to 0x7fffffff was also considered, but since C11's
char16_t also needs to be able to represent conversions of these
bytes, the surrogate range was the natural choice.

Internally regcomp needs to copy some iteration nodes before
translating the AST into TNFA representation.

Literal nodes were not copied correctly: the class type and list
of negated class types were not copied so classes were ignored
(in the non-negated case an ignored char class caused the literal
to match everything).

This affects iterations when the upper bound is finite, larger
than one or the lower bound is larger than one. So eg. the EREs

 [[:digit:]]{2}
 [^[:space:]ab]{1,4}

were treated as

 .{2}
 [^ab]{1,4}

The fix is done with minimal source modification to copy the
necessary fields, but the AST preparation and node handling
code of tre will need to be cleaned up for clarity.

The valid BRE backref tokens are \1 .. \9, and 0 is not a special
character either so \0 is undefined by the standard.

Such undefined escaped characters are treated as literal characters
currently, following existing practice, so \0 is the same as 0.

one of the features of ERE is that it's actually a regular language
and does not admit expressions which cannot be matched in linear time.
introduction of \n backref support into regcomp's ERE parsing was
unintentional.

the regex parser handles the (undefined) case of an unexpected byte
following a backslash as a literal. however, instead of correctly
decoding a character, it was treating the byte value itself as a
character. this was not only semantically unjustified, but turned out
to be dangerous on archs where plain char is signed: bytes in the
range 252-255 alias the internal codes -4 through -1 used for special
types of literal nodes in the AST.

The new code is a bit simpler and the generated code is about 1KB
smaller (on i386). The basic design was kept including internal
interfaces, TNFA generation was not touched.

The old tre parser had various issues:

[^aa-z]
negated overlapping ranges in a bracket expression were handled
incorrectly (eg [^aa-z] was handled as [^a] instead of [^a-z])

a{,2}
missing lower bound in a counted repetition should be an error,
but it was accepted with broken semantics: a{,2} was treated as
a{0,3}, the new parser rejects it

a{999,}
large min count was not rejected (a{5000,} failed with REG_ESPACE
due to reaching a stack limit), the new parser enforces the
RE_DUP_MAX limit

\xff
regcomp used to accept a pattern with illegal sequences in it
(treated them as empty expression so p\xffq matched pq) the new
parser rejects such patterns with REG_BADPAT or REG_ERANGE

[^b-fD-H] with REG_ICASE
old parser turned this into [^b-fB-F] because of the negated
overlapping range issue (see above), the new parser treats it
as [^b-hB-H], POSIX seems to require [^d-fD-F], but practical
implementations do case-folding first and negate the character
set later instead of the other way around. (Supporting the posix
way efficiently would require significant changes so it was left
as is, it is unclear if any application actually expects the
posix behaviour, this issue is raised on the austingroup tracker:
http://austingroupbugs.net/view.php?id=872 ).

another case-insensitive matching issue is that unicode case
folding rules can group more than two characters together while
towupper and towlower can only work for a pair of upper and
lower case characters, this is a limitation of POSIX so it is
not fixed.

invalid bracket and brace expressions may return different error
codes now (REG_ERANGE instead of REG_EBRACK or REG_BADBR instead
of REG_EBRACE) otherwise the new parser should be compatible with
the old one.

regcomp should be able to handle arbitrary pattern input if the
pattern length is limited, the only exception is the use of large
repetition counts (eg. (a{255}){255}) which require exp amount
of memory and there is no easy workaround.

for LC_MESSAGES, translation of strerror and similar literal message
functions is supported. for messages in other places (particularly the
dynamic linker) that use format strings, translation is not yet
supported. in order to make it possible and safe, such messages will
need to be refactored to separate the textual content from the format.

for LC_TIME, the day and month names and strftime-style format strings
provided by nl_langinfo are supported for translation. however there
may be limitations, as some of the original C-locale nl_langinfo
strings are non-unique and thus perhaps non-suitable as keys.

overall, the locale support activated by this commit should not be
seen as complete and polished but as a basis for beginning to test
locale functionality and implement locales.

per POSIX, the nmatch and pmatch arguments are ignored when the regex
was compiled with REG_NOSUB.

previously this flag was defined and accepted as a no-op, possibly
breaking some software that uses it. given the choice to remove the
definition and possibly break applications that were already working,
or simply implement the feature, the latter turned out to be easy
enough to make the decision easy.

in the case where the FNM_PATHNAME flag is also set, this
implementation is clean and essentially optimal. otherwise, it's an
inefficient "brute force" implementation. at some point, when cleaning
up and refactoring this code, I may add a more direct code path for
handling FNM_LEADING_DIR in the non-FNM_PATHNAME case, but at this
point my main interest is avoiding introducing new bugs in the code
that implements the standard fnmatch features specified by POSIX.

the FNM_PATHNAME logic for advancing by /-delimited components was
incorrect when the / character was escaped (i.e. \/), and a final \ at
the end of pattern was not handled correctly.

a '/' in the pattern could be incorrectly matched against the
terminating null byte in the string causing arbitrarily long
sequence of out-of-bounds access in fnmatch("/","",FNM_PATHNAME)

sizeof had incorrect argument in a few places, the size was always
large enough so the issue was not critical.

it's not clear to me at the moment whether the code that was removed
(and which is now being re-added) is needed, but it's far from being a
no-op, and i don't want to risk breaking regex in this release.

some structs and functions had reference to the params
feature of tre that is not used by the code anymore

pos_start local variable is not used in tre_tnfa_run_backtrack

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

TRE has a broken assumption that wchar_t is signed, which is a sane
expectation, but not required by the standard, and false on ARM's ABI.

i leave tre_char_t as wchar_t for now, since a pointer to it is
directly passed to functions that need pointer to wchar_t. it does not
seem to break anything. and since the maximum unicode scalar value is
0x10ffff, just use that explicitly rather than using the max value of
any particular C type.

these are cruft from the original code which used an explicit string
length rather than null termination. i blindly converted all the
checks to null terminator checks, without noticing that in several
cases, the subsequent switch statement would automatically handle the
null byte correctly.

i don't understand why this has to be conditional on being in BRE
mode, but enabling this code unconditionally breaks a huge number of
ERE test cases.

1. * in BRE is not special at the beginning of the regex or a
subexpression. this broke ncurses' build scripts.

2. \\( in BRE is a literal \ followed by a literal (, not a literal \
followed by a subexpression opener.

3. the ^ in \\(^ in BRE is a literal ^ only at the beginning of the
entire BRE. POSIX allows treating it as an anchor at the beginning of
a subexpression, but TRE's code for checking if it was at the
beginning of a subexpression was wrong, and fixing it for the sake of
supporting a non-portable usage was too much trouble when just
removing this non-portable behavior was much easier.

this patch also moved lots of the ugly logic for empty atom checking
out of the default/literal case and into new cases for the relevant
characters. this should make parsing faster and make the code smaller.
if nothing else it's a lot more readable/logical.

at some point i'd like to revisit and overhaul lots of this code...

unlike the old one, this one's algorithm does not suffer from
potential stack overflow issues or pathologically bad performance on
certain patterns. instead of backtracking, it uses a matching
algorithm which I have not seen before (unsure whether I invented or
re-invented it) that runs in O(1) space and O(nm) time. it may be
possible to improve the time to O(n), but not without significantly
greater complexity.

an invalid bracket expression must be treated as if the opening
bracket were just a literal character. this is to fix a bug whereby
POSIX left the behavior of the "[" shell command undefined due to it
being an invalid bracket expression.

the "< 0" test was always false due to use of an unsigned type. this
resulted in infinite loops on 32-bit machines (adding -1U to a pointer
is the same as adding -1) and crashes on 64-bit machines (offsetting
the string pointer by 4gb-1b when an illegal sequence was hit).

TRE wants to treat + and ? after a +, ?, or * as special; ? means
ungreedy and + is reserved for future use. however, this is
non-conformant. although redundant, these redundant characters have
well-defined (no-op) meaning for POSIX ERE, and are actually _literal_
characters (which TRE is wrongly ignoring) in POSIX BRE mode.

the simplest fix is to simply remove the unneeded nonstandard
functionality. as a plus, this shaves off a small amount of bloat.

the main practical results of this change are
1. the regex code is no longer subject to LGPL; it's now 2-clause BSD
2. most (all?) popular nonstandard regex extensions are supported

I hesitate to call this a "sync" since both the old and new code are
heavily modified. in one sense, the old code was "more severely"
modified, in that it was actively hostile to non-strictly-conforming
expressions. on the other hand, the new code has eliminated the
useless translation of the entire regex string to wchar_t prior to
compiling, and now only converts multibyte character literals as
needed.

in the future i may use this modified TRE as a basis for writing the
long-planned new regex engine that will avoid multibyte-to-wide
character conversion entirely by compiling multibyte bracket
expressions specific to UTF-8.

POSIX is unclear on whether it should, but all historical
implementations seem to behave this way, and it seems more useful to
applications.

patch by sh4rm4

basically there are 3 choices for how to implement this variable-size
string member:
1. C99 flexible array member: breaks using dirent.h with pre-C99 compiler.
2. old way: length-1 string: generates array bounds warnings in caller.
3. new way: length-NAME_MAX string. no problems, simplifies all code.

of course the usable part in the pointer returned by readdir might be
shorter than NAME_MAX+1 bytes, but that is allowed by the standard and
doesn't hurt anything.

this actually inadvertently disallows some valid patterns with
redundant / or * characters, but it's better than allowing unbounded
vla allocation.

eventually i'll write code to move the pattern to the stack and
eliminate redundancy to ensure that it fits in PATH_MAX at the
beginning of glob. this would also allow it to be modified in place
for passing to fnmatch rather than copied at each level of recursion.