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.
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.
Rich Felker