Previously, pattern matching and case mapping behavior branched based
on the provider. Refactor to use a method table, which is less
error-prone.
This is also a step toward multiple provider versions, which we may
want to support in the future.
Reviewed-by: Andreas Karlsson <andreas@proxel.se>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/2830211e1b6e6a2e26d845780b03e125281ea17b.camel%40j-davis.com
The PG_UNICODE_FAST locale uses code point sort order (fast,
memcmp-based) combined with Unicode character semantics. The character
semantics are based on Unicode full case mapping.
Full case mapping can map a single codepoint to multiple codepoints,
such as "ß" uppercasing to "SS". Additionally, it handles
context-sensitive mappings like the "final sigma", and it uses
titlecase mappings such as "Dž" when titlecasing (rather than plain
uppercase mappings).
Importantly, the uppercasing of "ß" as "SS" is specifically mentioned
by the SQL standard. In Postgres, UCS_BASIC uses plain ASCII semantics
for case mapping and pattern matching, so if we changed it to use the
PG_UNICODE_FAST locale, it would offer better compliance with the
standard. For now, though, do not change the behavior of UCS_BASIC.
Discussion: https://postgr.es/m/ddfd67928818f138f51635712529bc5e1d25e4e7.camel@j-davis.com
Discussion: https://postgr.es/m/27bb0e52-801d-4f73-a0a4-02cfdd4a9ada@eisentraut.org
Reviewed-by: Peter Eisentraut, Daniel Verite
Per git log, the last time someone tried to do something with
pgrminclude was around 2011. Many (not all) of the "pgrminclude
ignore" annotations are of a newer date but seem to have just been
copied around during refactorings and file moves and don't seem to
reflect an actual need anymore.
There have been some parallel experiments with include-what-you-use
(IWYU) annotations, but these don't seem to correspond very strongly
to pgrminclude annotations, so there is no value in keeping the
existing ones even for that kind of thing.
So, wipe them all away. We can always add new ones in the future
based on actual needs.
Discussion: https://www.postgresql.org/message-id/flat/2d4dc7b2-cb2e-49b1-b8ca-ba5f7024f05b%40eisentraut.org
In commit 08c0d6ad6 which introduced "rainbow" arcs in regex NFAs,
I didn't think terribly hard about what to do when creating the color
complement of a rainbow arc. Clearly, the complement cannot match any
characters, and I took the easy way out by just not building any arcs
at all in the complement arc set. That mostly works, but Nikolay
Shaplov found a case where it doesn't: if we decide to delete that
sub-NFA later because it's inside a "{0}" quantifier, delsub()
suffered an assertion failure. That's because delsub() relies on
the target sub-NFA being fully connected. That was always true
before, and the best fix seems to be to restore that property.
Hence, invent a new arc type CANTMATCH that can be generated in
place of an empty color complement, and drop it again later when we
start NFA optimization. (At that point we don't need to do delsub()
any more, and besides there are other cases where NFA optimization can
lead to disconnected subgraphs.)
It appears that this bug has no consequences in a non-assert-enabled
build: there will be some transiently leaked NFA states/arcs, but
they'll get cleaned up eventually. Still, we don't like assertion
failures, so back-patch to v14 where rainbow arcs were introduced.
Per bug #18708 from Nikolay Shaplov.
Discussion: https://postgr.es/m/18708-f94f2599c9d2c005@postgresql.org
Remove redundant checks for locale->collate_is_c now that we always
have a valid pg_locale_t.
Also, remove pg_locale_deterministic() wrapper, which is no longer
useful after commit e9931bfb75. Just check the field directly,
consistent with other fields in pg_locale_t.
Author: Andreas Karlsson
Discussion: https://postgr.es/m/60929555-4709-40a7-b136-bcb44cff5a3c@proxel.se
Instead always fetch the locale and look at the ctype_is_c field.
hba.c relies on regexes working for the C locale without needing
catalog access, which worked before due to a special case for
C_COLLATION_OID in lc_ctype_is_c(). Move the special case to
pg_set_regex_collation() now that lc_ctype_is_c() is gone.
Author: Andreas Karlsson
Discussion: https://postgr.es/m/60929555-4709-40a7-b136-bcb44cff5a3c@proxel.se
Set global variables after error paths so that they don't end up in an
inconsistent state.
The inconsistent state doesn't lead to an actual problem, because
after an error, pg_set_regex_collation() will be called again before
the globals are accessed.
Change extracted from patch by Andreas Karlsson, though not discussed
explicitly.
Discussion: https://postgr.es/m/60929555-4709-40a7-b136-bcb44cff5a3c@proxel.se
PG_REGEX_BUILTIN was added in f69319f2f1 but it did not follow the
same pattern as the previous labels, i.e. PG_LOCALE_*. In addition to
this, the two libc strategies did not include in the name that they were
related to this library.
The enum labels are renamed as PG_STRATEGY_type[_subtype] to make the
code clearer, in accordance to the library and the functions they rely
on.
Author: Andreas Karlsson
Discussion: https://postgr.es/m/6f81200f-68fd-411e-97a1-d1f291d2e222@proxel.se
Previously, passing NULL for pg_locale_t meant "use the libc provider
and the server environment". Now that the database collation is
represented as a proper pg_locale_t (not dependent on setlocale()),
remove special cases for NULL.
Leave wchar2char() and char2wchar() unchanged for now, because the
callers don't always have a libc-based pg_locale_t available.
Discussion: https://postgr.es/m/cfd9eb85-c52a-4ec9-a90e-a5e4de56e57d@eisentraut.org
Reviewed-by: Peter Eisentraut, Andreas Karlsson
The builtin C.UTF-8 locale has similar semantics to the libc locale of
the same name. That is, code point sort order (fast, memcmp-based)
combined with Unicode semantics for character operations such as
pattern matching, regular expressions, and
LOWER()/INITCAP()/UPPER(). The character semantics are based on
Unicode simple case mappings.
The builtin provider's C.UTF-8 offers several important advantages
over libc:
* faster sorting -- benefits from additional optimizations such as
abbreviated keys and varstrfastcmp_c
* faster case conversion, e.g. LOWER(), at least compared with some
libc implementations
* available on all platforms with identical semantics, and the
semantics are stable, testable, and documentable within a given
Postgres major version
Being based on memcmp, the builtin C.UTF-8 locale does not offer
natural language sort order. But it is an improvement for most use
cases that might otherwise use libc's "C.UTF-8" locale, as well as
many use cases that use libc's "C" locale.
Discussion: https://postgr.es/m/ff4c2f2f9c8fc7ca27c1c24ae37ecaeaeaff6b53.camel%40j-davis.com
Reviewed-by: Daniel Vérité, Peter Eisentraut, Jeremy Schneider
Since C99, there can be a trailing comma after the last value in an
enum definition. A lot of new code has been introducing this style on
the fly. Some new patches are now taking an inconsistent approach to
this. Some add the last comma on the fly if they add a new last
value, some are trying to preserve the existing style in each place,
some are even dropping the last comma if there was one. We could
nudge this all in a consistent direction if we just add the trailing
commas everywhere once.
I omitted a few places where there was a fixed "last" value that will
always stay last. I also skipped the header files of libpq and ecpg,
in case people want to use those with older compilers. There were
also a small number of cases where the enum type wasn't used anywhere
(but the enum values were), which ended up confusing pgindent a bit,
so I left those alone.
Discussion: https://www.postgresql.org/message-id/flat/386f8c45-c8ac-4681-8add-e3b0852c1620%40eisentraut.org
locale_t is defined by POSIX.1-2008 and SUSv4, and available on all
targeted systems. For Windows, win32_port.h redirects to a partial
implementation called _locale_t. We can now remove a lot of
compile-time tests for HAVE_LOCALE_T, and associated comments and dead
code branches that were needed for older computers.
Since configure + MinGW builds didn't detect locale_t but now we assume
that all systems have it, further inconsistencies among the 3 Windows build
systems were revealed. With this commit, we no longer define
HAVE_WCSTOMBS_L and HAVE_MBSTOWCS_L on any Windows build system, but
we have logic to deal with that so that replacements are available where
appropriate.
Reviewed-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Tristan Partin <tristan@neon.tech>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/CA%2BhUKGLg7_T2GKwZFAkEf0V7vbnur-NfCjZPKZb%3DZfAXSV1ORw%40mail.gmail.com
Run pgindent, pgperltidy, and reformat-dat-files.
This set of diffs is a bit larger than typical. We've updated to
pg_bsd_indent 2.1.2, which properly indents variable declarations that
have multi-line initialization expressions (the continuation lines are
now indented one tab stop). We've also updated to perltidy version
20230309 and changed some of its settings, which reduces its desire to
add whitespace to lines to make assignments etc. line up. Going
forward, that should make for fewer random-seeming changes to existing
code.
Discussion: https://postgr.es/m/20230428092545.qfb3y5wcu4cm75ur@alvherre.pgsql
For regex escape sequences, just test directly for the relevant ASCII
characters rather than using locale-sensitive character
classification.
This fixes an assertion failure when a locale considers a non-ASCII
character, such as "൧", to be a digit.
Reported-by: Richard Guo
Discussion: https://postgr.es/m/CAMbWs49Q6UoKGeT8pBkMtJGJd+16CBFZaaWUk9Du+2ERE5g_YA@mail.gmail.com
Backpatch-through: 11
Previously, a PostgreSQL-specific callback checked by the regex engine
had a way to trigger a special error code REG_CANCEL if it detected that
the next call to CHECK_FOR_INTERRUPTS() would certainly throw via
ereport().
A later proposed bugfix aims to move some complex logic out of signal
handlers, so that it won't run until the next CHECK_FOR_INTERRUPTS(),
which makes the above design impossible unless we split
CHECK_FOR_INTERRUPTS() into two phases, one to run logic and another to
ereport(). We may develop such a system in the future, but for the
regex code it is no longer necessary.
An earlier commit moved regex memory management over to our
MemoryContext system. Given that the purpose of the two-phase interrupt
checking was to free memory before throwing, something we don't need to
worry about anymore, it seems simpler to inject CHECK_FOR_INTERRUPTS()
directly into cancelation points, and just let it throw.
Since the plan is to keep PostgreSQL-specific concerns separate from the
main regex engine code (with a view to bein able to stay in sync with
other projects), do this with a new macro INTERRUPT(), customizable in
regcustom.h and defaulting to nothing.
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA%2BhUKGK3PGKwcKqzoosamn36YW-fsuTdOPPF1i_rtEO%3DnEYKSg%40mail.gmail.com
Previously, regex_t objects' memory was managed with malloc() and free()
directly. Switch to palloc()-based memory management instead.
Advantages:
* memory used by cached regexes is now visible with MemoryContext
observability tools
* cleanup can be done automatically in certain failure modes
(something that later commits will take advantage of)
* cleanup can be done in bulk
On the downside, there may be more fragmentation (wasted memory) due to
per-regex MemoryContext objects. This is a problem shared with other
cached objects in PostgreSQL and can probably be improved with later
tuning.
Thanks to Noah Misch for suggesting this general approach, which
unblocks later work on interrupts.
Suggested-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA%2BhUKGK3PGKwcKqzoosamn36YW-fsuTdOPPF1i_rtEO%3DnEYKSg%40mail.gmail.com
Autoconf is showing its age, fewer and fewer contributors know how to wrangle
it. Recursive make has a lot of hard to resolve dependency issues and slow
incremental rebuilds. Our home-grown MSVC build system is hard to maintain for
developers not using Windows and runs tests serially. While these and other
issues could individually be addressed with incremental improvements, together
they seem best addressed by moving to a more modern build system.
After evaluating different build system choices, we chose to use meson, to a
good degree based on the adoption by other open source projects.
We decided that it's more realistic to commit a relatively early version of
the new build system and mature it in tree.
This commit adds an initial version of a meson based build system. It supports
building postgres on at least AIX, FreeBSD, Linux, macOS, NetBSD, OpenBSD,
Solaris and Windows (however only gcc is supported on aix, solaris). For
Windows/MSVC postgres can now be built with ninja (faster, particularly for
incremental builds) and msbuild (supporting the visual studio GUI, but
building slower).
Several aspects (e.g. Windows rc file generation, PGXS compatibility, LLVM
bitcode generation, documentation adjustments) are done in subsequent commits
requiring further review. Other aspects (e.g. not installing test-only
extensions) are not yet addressed.
When building on Windows with msbuild, builds are slower when using a visual
studio version older than 2019, because those versions do not support
MultiToolTask, required by meson for intra-target parallelism.
The plan is to remove the MSVC specific build system in src/tools/msvc soon
after reaching feature parity. However, we're not planning to remove the
autoconf/make build system in the near future. Likely we're going to keep at
least the parts required for PGXS to keep working around until all supported
versions build with meson.
Some initial help for postgres developers is at
https://wiki.postgresql.org/wiki/Meson
With contributions from Thomas Munro, John Naylor, Stone Tickle and others.
Author: Andres Freund <andres@anarazel.de>
Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Author: Peter Eisentraut <peter@eisentraut.org>
Reviewed-By: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/20211012083721.hvixq4pnh2pixr3j@alap3.anarazel.de
Adjust a handful of remaining function prototypes that were overlooked
by recent commit bc2187ed. This oversight wasn't caught by clang-tidy
because the functions in question are only built in custom REG_DEBUG
builds.
Author: Peter Geoghegan <pg@bowt.ie>
Reported-By: Tom Lane <tgl@sss.pgh.pa.us>
Make regex code consistently use named parameters in function
declarations. Also make sure that parameter names from each function's
declaration match corresponding definition parameter names.
This makes Henry Spencer's regex code follow Postgres coding standards.
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAH2-WznJt9CMM9KJTMjJh_zbL5hD9oX44qdJ4aqZtjFi-zA3Tg@mail.gmail.com
SplitToVariants() in the ispell code, lseg_inside_poly() in geo_ops.c,
and regex_selectivity_sub() in selectivity estimation could recurse
until stack overflow; fix by adding check_stack_depth() calls.
So could next() in the regex compiler, but that case is better fixed by
converting its tail recursion to a loop. (We probably get better code
that way too, since next() can now be inlined into its sole caller.)
There remains a reachable stack overrun in the Turkish stemmer, but
we'll need some advice from the Snowball people about how to fix that.
Per report from Egor Chindyaskin and Alexander Lakhin. These mistakes
are old, so back-patch to all supported branches.
Richard Guo and Tom Lane
Discussion: https://postgr.es/m/1661334672.728714027@f473.i.mail.ru
Previously, callers of pg_newlocale_from_collation() did not call it
if the collation was DEFAULT_COLLATION_OID and instead proceeded with
a pg_locale_t of 0. Instead, now we call it anyway and have it return
0 if the default collation was passed. It already did this, so we
just have to adjust the callers. This simplifies all the call sites
and also makes future enhancements easier.
After discussion and testing, the previous comment in pg_locale.c
about avoiding this for performance reasons may have been mistaken
since it was testing a very different patch version way back when.
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Discussion: https://www.postgresql.org/message-id/ed3baa81-7fac-7788-cc12-41e3f7917e34@enterprisedb.com
If search_start is greater than the length of the string, we should just
return REG_NOMATCH immediately. (Note that the equality case should
*not* be rejected, since the pattern might be able to match zero
characters.) This guards various internal assumptions that the min of a
range of string positions is not more than the max. Violation of those
assumptions could allow an attempt to fetch string[search_start-1],
possibly causing a crash.
Jaime Casanova pointed out that this situation is reachable with the
new regexp_xxx functions that accept a user-specified start position.
I don't believe it's reachable via any in-core call site in v14 and
below. However, extensions could possibly call pg_regexec with an
out-of-range search_start, so let's back-patch the fix anyway.
Discussion: https://postgr.es/m/20210911180357.GA6870@ahch-to
I wrote this while thinking about a possible optimization, but it's
a useful description of the existing code regardless of whether the
optimization ever happens. So push it separately.
Second thoughts about commit 824bf7190: we apply makesearch() to
an NFA after having determined whether it is a MATCHALL pattern.
Prepending ".*" doesn't make it non-MATCHALL, but it does change the
maximum possible match length, and makesearch() failed to update that.
This has no ill effects given the stylized usage of search NFAs, but
it seems like it's better to keep the data structure consistent. In
particular, fixing this allows more honest handling of the MATCHALL
check in matchuntil(): we can now assert that maxmatchall is infinity,
instead of lamely assuming that it should act that way.
In passing, improve the code in dump[c]nfa so that infinite maxmatchall
is printed as "inf" not a magic number.
Regexps like "(.){0}...\1" drew an "invalid backreference number".
That's not unreasonable on its face, since the capture group will
never be matched if it's iterated zero times. However, other engines
such as Perl's don't complain about this, nor do we throw an error for
related cases such as "(.)|\1", even though that backref can never
succeed either. Also, if the zero-iterations case happens at runtime
rather than compile time --- say, "(x)*...\1" when there's no "x" to
be found --- that's not an error, we just deem the backref to not
match. Making this even less defensible, no error was thrown for
nested cases such as "((.)){0}...\2"; and to add insult to injury,
those cases could result in assertion failures instead. (It seems
that nothing especially bad happened in non-assert builds, though.)
Let's just fix it so that no error is thrown and instead the backref
is deemed to never match, so that compile-time detection of no
iterations behaves the same as run-time detection.
Per report from Mark Dilger. This appears to be an aboriginal error
in Spencer's library, so back-patch to all supported versions.
Pre-v14, it turns out to also be necessary to back-patch one aspect of
commits cb76fbd7e/00116dee5, namely to create capture-node subREs with
the begin/end states of their subexpressions, not the current lp/rp
of the outer parseqatom invocation. Otherwise delsub complains that
we're trying to disconnect a state from itself. This is a bit scary
but code examination shows that it's safe: in the pre-v14 code, if we
want to wrap iteration around the subexpression, the first thing we do
is overwrite the atom's begin/end fields with new states. So the
bogus values didn't survive long enough to be used for anything, except
if no iteration is required, in which case it doesn't matter.
Discussion: https://postgr.es/m/A099E4A8-4377-4C64-A98C-3DEDDC075502@enterprisedb.com
The recursion in cdissect() was careless about clearing match data
for capturing parentheses after rejecting a partial match. This
could allow a later back-reference to succeed when by rights it
should fail for lack of a defined referent.
To fix, think a little more rigorously about what the contract
between different levels of cdissect's recursion needs to be.
With the right spec, we can fix this using fewer rather than more
resets of the match data; the key decision being that a failed
sub-match is now explicitly responsible for clearing any matches
it may have set.
There are enough other cross-checks and optimizations in the code
that it's not especially easy to exhibit this problem; usually, the
match will fail as-expected. Plus, regexps that are even potentially
vulnerable are most likely user errors, since there's just not much
point in writing a back-ref that doesn't always have a referent.
These facts perhaps explain why the issue hasn't been detected,
even though it's almost certainly a couple of decades old.
Discussion: https://postgr.es/m/151435.1629733387@sss.pgh.pa.us
After detecting a sub-match "dissect" failure (i.e., a backref match
failure) in the i'th sub-match of an iteration node, we should proceed
by adjusting the attempted length of the i'th submatch. As coded,
though, these functions changed the attempted length of the *last*
sub-match, and only after exhausting all possibilities for that would
they back up to adjust the next-to-last sub-match, and then the
second-from-last, etc; all of which is wasted effort, since only
changing the start or length of the i'th sub-match can possibly make
it succeed. This oversight creates the possibility for exponentially
bad performance. Fortunately the problem is masked in most cases by
optimizations or constraints applied elsewhere; which explains why
we'd not noticed it before. But it is possible to reach the problem
with fairly simple, if contrived, regexps.
Oversight in my commit 173e29aa5. That's pretty ancient now,
so back-patch to all supported branches.
Discussion: https://postgr.es/m/1808998.1629412269@sss.pgh.pa.us
The functions moveins(), copyins(), moveouts(), copyouts() are
required to preserve the invariant that there are no duplicate arcs in
the regex's NFA. Spencer's original implementation of them was O(N^2)
since it checked separately for a match to each source arc. In commit
579840ca0 I improved that by adding sort/merge logic to be used if
more than a few arcs are to be moved/copied. However, I now realize
that that missed a bet. At many call sites, the target state is newly
made and cannot have any existing in-arcs (respectively out-arcs)
that could be duplicates. So spending any cycles at all on checking
for duplicates is wasted effort; in these cases we can just blindly
move/copy all the source arcs. Add code paths to do that.
It turns out that for copyins()/copyouts(), *all* the call sites have
this property, making all the "improved" logic in them flat out
unreachable. Perhaps we'll need the full capability again someday,
so I just #ifdef'd those paths out rather than removing them entirely.
In passing, add a few test cases to improve code coverage in this
area as well as in regc_locale.c/regc_pg_locale.c.
Discussion: https://postgr.es/m/810272.1629064063@sss.pgh.pa.us
Identifying the precise match locations for parenthesized subexpressions
is a fairly expensive task given the way our regexp engine works, both
at regexp compile time (where we must create an optimized NFA for each
parenthesized subexpression) and at runtime (where determining exact
match locations requires laborious search).
Up to now we've made little attempt to optimize this situation. This
patch identifies cases where we know at compile time that we won't
need to know subexpression match locations, and teaches the regexp
compiler to not bother creating per-subexpression regexps for
parenthesis pairs that are not referenced by backrefs elsewhere in
the regexp. (To preserve semantics, we obviously still have to
pin down the match locations of backref references.) Users could
have obtained the same results before this by being careful to
write "non capturing" parentheses wherever possible, but few people
bother with that.
Discussion: https://postgr.es/m/2219936.1628115334@sss.pgh.pa.us
I had committer's remorse almost immediately after pushing cb76fbd7e,
upon finding that removing capturing subexpressions' subREs from the
data structure broke my proposed patch for REG_NOSUB optimization.
Revert that data structure change. Instead, address the concern
about not changing capturing subREs' endpoints by not changing the
endpoints. We don't need to, because the point of that bit was just
to ensure that the atom has endpoints distinct from the outer state
pair that we're stringing the branch between. We already made
suitable states in the parenthesized-subexpression case, so the
additional ones were just useless overhead. This seems more
understandable than Spencer's original coding, and it ought to be
a shade faster too by saving a few state creations and arc changes.
(I actually see a couple percent improvement on Jacobson's web
corpus, though that's barely above the noise floor so I wouldn't
put much stock in that result.)
Also, fix the logic added by ea1268f63 to ensure that the subRE
recorded in v->subs[subno] is exactly the one with capno == subno.
Spencer's original coding recorded the child subRE of the capture
node, which is okay so far as having the right endpoint states is
concerned, but as of cb76fbd7e the capturing subRE itself always
has those endpoints too. I think the inconsistency is confusing
for the REG_NOSUB optimization.
As before, backpatch to v14.
Discussion: https://postgr.es/m/0203588E-E609-43AF-9F4F-902854231EE7@enterprisedb.com
Up to now, we remembered the definition of a capturing parenthesis
subexpression by storing a pointer to the associated subRE node.
That was okay before, because that subRE didn't get modified anymore
while parsing the rest of the regexp. However, in the wake of
commit ea1268f63, that's no longer true: the outer invocation of
parseqatom() feels free to scribble on that subRE. This seems to
work anyway, because the states we jam into the child atom in the
"prepare a general-purpose state skeleton" stanza aren't really
semantically different from the original endpoints of the child atom.
But that would be mighty easy to break, and it's definitely not how
things worked before.
Between this and the issue fixed in the prior commit, it seems best
to get rid of this dependence on subRE nodes entirely. We don't need
the whole child subRE for future backrefs, only its starting and ending
NFA states; so let's just store pointers to those.
Also, in the corner case where we make an extra subRE to handle
immediately-nested capturing parentheses, it seems like it'd be smart
to have the extra subRE have the same begin/end states as the original
child subRE does (s/s2 not lp/rp). I think that linking it from lp to
rp might actually be semantically wrong, though since Spencer's original
code did it that way, I'm not totally certain. Using s/s2 is certainly
not wrong, in any case.
Per report from Mark Dilger. Back-patch to v14 where the problematic
patches came in.
Discussion: https://postgr.es/m/0203588E-E609-43AF-9F4F-902854231EE7@enterprisedb.com
Commit cebc1d34e taught parseqatom() to optimize cases where a branch
contains only one, "messy", atom by getting rid of excess subRE nodes.
The way we really should do that is to keep the subRE built for the
"messy" child atom; but to avoid changing parseqatom's nominal API,
I made it delete that node after copying its fields to the outer subRE
made by parsebranch(). It seems that that actually worked at the time;
but it became dangerous after ea1268f63, because that later commit
allowed the lower invocation of parse() to return a subRE that was also
pointed to by some v->subs[] entry. This meant we could wind up with a
dangling pointer in v->subs[], allowing a later backref to misbehave,
but only if that subRE struct had been reused in between. So the damage
seems confined to cases like '((...))...(...\2'.
To fix, do what I should have done before and modify parseqatom's API
to make it possible for it to remove the caller's subRE instead of the
callee's. That's safer because we know that subRE isn't complete yet,
so noplace else will have a pointer to it.
Per report from Mark Dilger. Back-patch to v14 where the problematic
patches came in.
Discussion: https://postgr.es/m/0203588E-E609-43AF-9F4F-902854231EE7@enterprisedb.com
Commit 824bf7190 introduced a new search of the NFAs generated by
regex compilation. I failed to think hard about the performance
characteristics of that search, with the predictable outcome
that it's bad: weird regexes can trigger exponential search time.
Worse, there's no check-for-interrupt in that code, so you can't
even cancel the query if this happens.
Fix by introducing memo-ization of the search results, so that any one
NFA state need be examined in detail just once. This potentially uses
a lot of memory, but we can bound the memory usage by putting a limit
on the number of states for which we'll try to prove match-all-ness.
That is sane because we already have a limit (DUPINF) on the maximum
finite string length that a matchall regex can match; and patterns
that involve much more than DUPINF states would probably exceed that
limit anyway.
Also, rearrange the logic so that we check the basic is-the-graph-
all-RAINBOW-arcs property before we start the recursive search to
determine path lengths. This will ensure that we fall out quickly
whenever the NFA couldn't possibly be matchall.
Also stick in a check-for-interrupt, just in case these measures
don't completely eliminate the risk of slowness.
Discussion: https://postgr.es/m/3483895.1619898362@sss.pgh.pa.us
Coverity is still unhappy after commit 190c79884, and after looking
closer I think it might be onto something. The callers of newdfa()
typically drop out if v->err has been set nonzero, which newdfa()
is faithfully doing if it fails. However, what if v->err was already
nonzero before we entered newdfa()? Then newdfa() could succeed and
the caller would promptly leak its result.
I don't think this scenario can actually happen, but the predicate
"v->err is always zero when newdfa() is called" seems difficult to be
entirely sure of; there's a good deal of code that potentially could
get that wrong.
It seems better to adjust the callers to directly check for a null
result instead of relying on ISERR() tests. This is slightly cheaper
than the previous coding anyway.
Lacking evidence that there's any real bug, no back-patch.
This extends the changes made in commit cebc1d34e, teaching
parseqatom() to generate fewer or cheaper subre nodes in some edge
cases. The case of interest here is a quantified atom that is "messy"
only because it has greediness opposite to what preceded it (whereas
captures and backrefs are intrinsically messy). In this case we don't
need an iteration node, since we don't care where the sub-matches of
the quantifier are; and we might also not need a second concatenation
node. This seems of only marginal real-world use according to my
testing, but I wanted to get it in before wrapping up this series of
regex performance fixes.
Discussion: https://postgr.es/m/1340281.1613018383@sss.pgh.pa.us
In some cases, at the time that we're doing an NFA-based precheck
of whether a backref subexpression can match at a particular place
in the string, we already know which substring the referenced
subexpression matched. If so, we might as well forget about the NFA
and just compare the substring; this is faster and it gives an exact
rather than approximate answer.
In general, this optimization can help while we are prechecking within
the second child expression of a concat node, while the capture was
within the first child expression; then the substring was saved during
cdissect() of the first child and will be available to NFA checks done
while cdissect() recurses into the second child. It can help quite a
lot if the tree looks like
concat
/ \
capture concat
/ \
expensive stuff backref
as we will be able to avoid recursively dissecting the "expensive
stuff" before discovering that the backref isn't satisfied with a
particular midpoint that the lower concat node is testing. This
doesn't help if the concat tree is left-deep, as the capture node
won't get set soon enough (and it's hard to fix that without changing
the engine's match behavior). Fortunately, right-deep concat trees
are the common case.
Patch by me, reviewed by Joel Jacobson
Discussion: https://postgr.es/m/661609.1614560029@sss.pgh.pa.us
POSIX defines the behavior of back-references thus:
The back-reference expression '\n' shall match the same (possibly
empty) string of characters as was matched by a subexpression
enclosed between "\(" and "\)" preceding the '\n'.
As far as I can see, the back-reference is supposed to consider only
the data characters matched by the referenced subexpression. However,
because our engine copies the NFA constructed from the referenced
subexpression, it effectively enforces any constraints therein, too.
As an example, '(^.)\1' ought to match 'xx', or any other string
starting with two occurrences of the same character; but in our code
it does not, and indeed can't match anything, because the '^' anchor
constraint is included in the backref's copied NFA. If POSIX intended
that, you'd think they'd mention it. Perl for one doesn't act that
way, so it's hard to conclude that this isn't a bug.
Fix by modifying the backref's NFA immediately after it's copied from
the reference, replacing all constraint arcs by EMPTY arcs so that the
constraints are treated as automatically satisfied. This still allows
us to enforce matching rules that depend only on the data characters;
for example, in '(^\d+).*\1' the NFA matching step will still know
that the backref can only match strings of digits.
Perhaps surprisingly, this change does not affect the results of any
of a rather large corpus of real-world regexes. Nonetheless, I would
not consider back-patching it, since it's a clear compatibility break.
Patch by me, reviewed by Joel Jacobson
Discussion: https://postgr.es/m/661609.1614560029@sss.pgh.pa.us
Jeff Davis