Getting "Invalid Regular Expression" for an extremely simple expression

Alan Kilborn

Regarding your Test_OK.txt and Test_KO.txt files…

I have a resident script that shows me, e.g., “Found match 6 of 27” on the Find window’s status bar when I press Find Next.

I noticed that when trying your test for the Test_OK.txt file, my script crashes with this error in the PythonScript console window:

editor.research(find_what_regex_text, lambda m: retval_list.append(m.span(0)))
RuntimeError: The complexity of matching the regular expression exceeded predefined bounds.  Try refactoring the regular expression to make each choice made by the state machine unambiguous.  This exception is thrown to prevent "eternal" matches that take an indefinite period time to locate.

Again note that this is for the Test_OK.txt file, where Notepad++ itself has no problem finding the match.

My understanding is that PythonScript integrates its own copy of Boost, so, one would think, with all other things being equal (ha!), that it would succeed when N++ succeeds. But clearly something is not equal.

I thought this just another interesting tidbit in this topic’s “journey”. :-)

Coises

@Alan-Kilborn said in Getting "Invalid Regular Expression" for an extremely simple expression:

My understanding is that PythonScript integrates its own copy of Boost, so, one would think, with all other things being equal (ha!), that it would succeed when N++ succeeds. But clearly something is not equal.

There is a macro variable, BOOST_REGEX_MAX_STATE_COUNT, that influences one of the limits Boost::regex tests when evaluating whether to issue that message. Notepad++ leaves it at its default value, but it is possible that Python changes it.

Scott Gartner

@PeterJones said in Getting "Invalid Regular Expression" for an extremely simple expression:

or (?-m)^.*[^"]*test$ but that just results in “Invalid regular expression.”

The first resulted in Invalid Regular Expression; the second just finds no match, because you’ve told it that ^ should only match the beginning of the file and $ should only match the end of the file, and your file is more than one line long.

Well damn, you’re right. I was sure it gave me a syntax error for both of my examples. I must have gotten myself confused while I was testing.

Now that I see that, from my testing, (?-m) means ^$ should match the beginning and end of the same line (no intervening LF) and (?m) (the default for NP++) means ^$ has to match the beginning and end of any line in the file. So (?-m) absolutely affects the [^"]* portion of the RE.

PeterJones

@Scott-Gartner ,

Now that I see that, from my testing, (?-m) means ^$ should match the beginning and end of the same line (no intervening LF) and (?m) (the default for NP++) means ^$ has to match the beginning and end of any line in the file. So (?-m) absolutely affects the [^"]* portion of the RE.

I guess I used loose terminology when I described what (?m) / (?-m) affect. I should have said those options affect the beginning-of-line ^ anchor and the end-of-line $ anchor.

They don’t affect all ^ symbols, because in some locations, like the beginning of a character class where it negates the character class, and has nothing to do with the beginning-of-line-anchor ^ . To clarify, [^"] literally means “the class that contains every character that is not the ASCII double-quote”, and the ^ in that class is the class-negation operator, it is not the beginning-of-line anchor nor the literal ASCII caret character.

With those definitions, I cannot see how (?m) / (?-m) affect [^"]* . But, maybe I’m wrong. Can you share a text file and regex where they change the meaning of the [^"]* ? (It would have to be something other than a regex that contains a ^ or $ anchor, because those two anchors are affected by the m-option)

Further, your statement of what the anchors mean in the non-multiline context (“(?-m) means ^$ should match the beginning and end of the same line (no intervening LF)”) is not phrased in a way that matches with my experience and understanding of the specs. But maybe I am not interpreting that phrase in the way you intended.

For this example, I will start with a 3-line file (ie, no empty line 4)

This file
has multiple
lines in it

If I run the regex (?m)^ and hit Find Next repeatedly, it will match at three locations, because ^ can match any beginning-of-line in that mode. If I run the regex (?-m)^ , Find Next will only match the beginning of the first line, not the beginning of lines 2 or 3, because (?-m) restricts ^ to only be the beginning of the string rather than of any line (where, in Notepad++, the string is either the entire file). Similarly, (?m)$ will match the end of lines 1, 2, and 3; whereas (?-m)$ will only match the end of the last line of the file.

Your phrasing indicates to me that you think that the ^ and $ have to be on the same line in (?-m) mode, but my examples show that’s not right – but again, maybe I am misunderstanding your sentence.

Combining the two ideas: the example file has no quote marks, so [^"]* will match all the non-quote characters the same file). Thus, (?m)^[^"]*$ will match from the beginning of the file to the end, as will (?-m)^[^"]*$ – the m-state is irrelevant. Then make it non-greedy: (?m)^[^"]*?$ will only match one line at a time, because the $ causes the non-greedy section before it to stop at the first end-of-line found; on the other hand, (?-m)^[^"]*?$ will still match the entire file – because the ^ anchor only matches at one location in the entire file (at the beginning) and the $ anchor only ; in this non-greedy, the m-state changes the meaning of the ^ and $ anchors, not the meaning of the [^"]*? .

guy038

Hello, @scott-gartner, @alan-kilborn, @coises, @mkupper, @mark-Olson, @terry-r, @peterjones and All,

As mentionned by @alan-kilborn, I found out some spare time to download and test my two files Test_1_OK.txt and Test_2_KO.txt with the GrepWin software

So, here is, below, the road map for testing.

In a new folder, put the two files Test_1_OK.txt and Test_2_KO.txt, already tested within Notepad++
Download, in this folder, the last portable x64 version from :

https://github.com/stefankueng/grepWin/releases/download/2.1.1/grepWin-x64-2.1.1_portable.zip

Double-click on file grepWin-x64-2.1.1_portable.zip
Extract the single file grepWin-x64-2.1.1_portable.exe, in this folder
Double-click on file grepWin-x64-2.1.1_portable.exe

=> You should get this picture :

Enter the name of the new folder in the Search in zone
Select Regex search mode
Enter ".*employeeId" in the Search for zone
Check the Treat Files as UTF8 box option
Enter *.txt ( or more exactly Test_?_??.txt ) in the Find names match zone
Finally, click on the Search button

After 2 / 3 seconds, you should get this picture :

As you can see :

It does find one match, regarding the Test_1_OK.txt file
It find a Regex stack error, regarding the Test_2_KO.txt file

It quite obvious that the results are strictely identical to the ones obtained from within N++. Particularly, note that the error message, regarding Test_2_KO.txt file, is also the same as the one shown in the N++ search dialog, which proves that the error message is a Boost message itself !!

Thus, it seems to me that this bug can be considered rather a Boost Engine bug !

Now, if, at the bottom, we click on the Content button, we get this picture :

Note that it does show that one match has been found, either, in the Test_2_KO.txt file !

Finally, the last picture just confirms that I did my tests with the last GrepWin 2.1.1 release :

Now, should we ask John Maddock about it ? There are probably a lot of other BORDER cases ! Its’s a combination of a specific regular expression with specific data. As @coises said :

The message is the result of a heuristic, not a mathematically exact determination. It doesn’t mean the regular expression is technically invalid, it means that, when applied to the data in question, it appears to be very inefficient (possibly — not necessarily — non-terminating).

For these special cases, the best to do is, indeed, to refactor the regular expression, in order that each part can be considered as unambiguous !!

Best Regards,

guy038

Coises

@guy038 said in Getting "Invalid Regular Expression" for an extremely simple expression:

There are probably a lot of other BORDER cases

If you’re up for some reading about theory, take a look here:

https://swtch.com/~rsc/regexp/

The super-short version of that is that regular expression matching can be very efficient (linear in the length of the text being matched) if you allow only the most basic, original syntax of regular expressions. Once you support things like capture groups, non-greedy repeats and (especially) back references, the time can be at least quadratic (and I think sometimes even worse) in the length of the text to be examined.

It would seem that it should be possible to try a regular expression with an efficient engine first; if it parses, the job is done; if it says the expression isn’t valid within the more limited syntax of the efficient engine, then give it to the potentially slow but more comprehensive engine.

Alan Kilborn

@Coises said in Getting "Invalid Regular Expression" for an extremely simple expression:

It would seem that it should be possible to try a regular expression with an efficient engine first; if it parses, the job is done; if it says the expression isn’t valid within the more limited syntax of the efficient engine, then give it to the potentially slow but more comprehensive engine.

Are you proposing that Notepad++ implement something like this?

Coises

@Alan-Kilborn said in Getting "Invalid Regular Expression" for an extremely simple expression:

Are you proposing that Notepad++ implement something like this?

I was more “speculating” than “proposing.”

I think I’d want to see proof of value of something like this in a plugin — perhaps the search in my own Columns++, or perhaps in @Thomas-Knoefel’s MultiReplace — before I would suggest changing the implementation of a fundamental feature of Notepad++ itself (though in principle it would be transparent to users, just faster and with fewer of these obscure “complexity” messages).

guy038

Hello, @coises and All,

@coises, I searched a bit on the Internet and, according to an article of https://stackoverflow.com, I came across a series of tests to compare different regular expression engines :

The older was provided by John Maddowck, in 2003 :

https://www.boost.org/doc/libs/1_41_0/libs/regex/doc/gcc-performance.html

An other one, on GitHub, with the same tests, was last modified in 2015 :

https://zherczeg.github.io/sljit/regex_perf.html

The most recent, from the Rust community, with the same tests, either, in 2018 :

https://rust-leipzig.github.io/regex/2017/03/28/comparison-of-regex-engines/

You can get the main test text, from the Gutenberg project at :

http://www.gutenberg.org/files/3200/old/mtent12.zip

And here is the results of these tests :

https://i.sstatic.net/ORL3Z.png

From this picture, here are the different links to get information about all these regex libraries, in the order from left to right :

https://github.com/hanickadot/compile-time-regular-expressions

https://github.com/google/re2

https://theboostcpplibraries.com/boost.regex

https://cplusplus.com/reference/regex/

https://github.com/PCRE2Project/pcre2

https://www.pcre.org/current/doc/html/pcre2matching.html

https://www.pcre.org/original/doc/html/pcrejit.html

https://github.com/kkos/oniguruma

https://github.com/laurikari/tre

https://github.com/intel/hyperscan

https://github.com/rust-lang/regex

https://docs.rs/regex/latest/regex/struct.Regex.html ( not totally sure ? )

For instance, I did a try of the last text regex (.*?,){13}z against the complete mtent12.txt test file, extracted from the mtent12.zip archive, which, of course, fails miserably :-((

Then, I tried this other regex formulation (?:[^,]*,){13}[\u\l], without success, too ! However, I noticed that beginning at line 500,000 and searching downward does find one match !

So, I changed my strategy and simply marked all matches of the regex ,[\u\l]. As, normally, any comma is always followed with a space char, I should not get many matchs !

As planned, I got 11 matches : a comma followed with a lower-case letter ! ( ,a × 2, ,b, ,g, ,h, ,m, ,n ,,s × 2, ,t and ,w )

Note that the requested case ,z does not exist at all !

And when moving the caret, let’s say, 100 - 200 lines before each of these matches, it allowed me to easily get all these matches !

At this point, I tried to select all the zones around these 11 matches in a small new file, that I named Matches.txt. Then, using the Mark dialog with (?:[^,]*,){13}[\u\l], against this small file, it does return 10 matches ( not 11 as explained in the next post ! )

However, it is distressing to note that the equivalent regex (?:.*?,){13}[\u\l] still fails against this tiny Matches.txt file, of only 16,138 bytes :-((

Unfortunately, it’s quite certain that cases, like that one, may arise when using most of the available regex engines !

In the next post, you’ll find the Matches.txt contents, for any further testing. My default test, which works nicely, is to mark multi-lines text, matching the (?:[^,]*,){13}[\u\l] regex !

Best Regards,

guy038

guy038

Hi,All,

================================================================================ BEGINNING of file
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more insupportable the clatter became, the more enchanted they all

appeared to be.  When there was silence, Mrs Sellers lifted upon

Washington a face that beamed with a childlike pride, and said:



"It belonged to his grandmother."



The look and the tone were a plain call for admiring surprise, and

therefore Washington said (it was the only thing that offered itself at

the moment:)



"Indeed!"



"Yes, it did, didn't it father!" exclaimed one of the twins.  "She was my

great-grandmother--and George's too; wasn't she, father!  You never saw

her, but Sis has seen her, when Sis was a baby-didn't you, Sis!  Sis has

seen her most a hundred times.  She was awful deef--she's dead, now.

Aint she, father!"



All the children chimed in, now, with one general Babel of information

about deceased--nobody offering to read the riot act or seeming to

discountenance the insurrection or disapprove of it in any way--but the

head twin drowned all the turmoil and held his own against the field:



"It's our clock, now--and it's ,got wheels inside of it, and a thing that

flatters every time she strikes--don't it, father!  Great-grandmother

died before hardly any of us was born--she was an Old-School Baptist and
================================================================================ Line 76,527 ===
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    Welcome and home were mine within this State,

      Whose vales I leave -- whose spires fade fast from me

    And cold must be mine eyes, and heart, and tete,

      When, dear Alabama! they turn cold on thee!"



There were very few there who knew what "tete"

meant, but the poem was very satisfactory, nevertheless.



Next appeared a dark-complexioned, black-eyed,

black-haired young lady, who paused an impressive

moment, assumed a tragic expression, and began to

read in a measured, solemn tone:



  "A VISION



   "Dark and tempestuous was night. Around the

   throne on high not a single star quivered; but

   the deep intonations of the heavy thunder

   constantly vibrated upon the ear; whilst the

   terrific lightning revelled in angry mood

   through the cloudy chambers of heaven, seeming

   to scorn the power exerted over its terror by

   the illustrious Franklin! Even the boisterous

   winds unanimously came forth from their mystic

   homes, and blustered about as if to enhance by

   their aid the wildness of the scene.



   "At such a time,so dark,so dreary, for human

   sympathy my very spirit sighed; but instead thereof,
================================================================================ Line 147,967 ===
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Then I told her my father and mother was dead, and

the law had bound me out to a mean old farmer in the

country thirty mile back from the river, and he treated

me so bad I couldn't stand it no longer; he went away

to be gone a couple of days, and so I took my chance

and stole some of his daughter's old clothes and

cleared out, and I had been three nights coming the

thirty miles. I traveled nights, and hid daytimes and

slept, and the bag of bread and meat I carried from

home lasted me all the way, and I had a-plenty. I

said I believed my uncle Abner Moore would take care

of me, and so that was why I struck out for this town

of Goshen.



"Goshen, child? This ain't Goshen. This is St.

Petersburg. Goshen's ten mile further up the river.

Who told you this was Goshen?"



"Why, a man I met at daybreak this morning, just

as I was going to turn into the woods for my regular

sleep. He told me when the roads forked I must take

the right hand, and five mile would fetch me to

Goshen."



"He was drunk, I reckon. He told you just ex-

actly wrong."



"Well,,he did act like he was drunk, but it ain't no

matter now. I got to be moving along. I'll fetch

Goshen before daylight."
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all busted up and ruined, because they could have the

heart to serve Jim such a trick as that, and make him

a slave again all his life, and amongst strangers, too,

for forty dirty dollars.



Once I said to myself it would be a thousand times

better for Jim to be a slave at home where his family

was, as long as he'd GOT to be a slave, and so I'd better

write a letter to Tom Sawyer and tell him to tell Miss

Watson where he was. But I soon give up that notion

for two things: she'd be mad and disgusted at his

rascality and ungratefulness for leaving her, and so

she'd sell him straight down the river again; and if

she didn't, everybody naturally despises an ungrateful

nigger, and they'd make Jim feel it all the time, and so

he'd feel ornery and disgraced. And then think of

ME! It would get all around that Huck Finn helped a

nigger to get his freedom; and if I was ever to see

anybody from that town again I'd be ready to get

down and lick his boots for shame. That's just the

way: a person does a low-down thing, and then he

don't want to take no consequences of it. Thinks as

long as he can hide, it ain't no disgrace. That was

my fix exactly. The more I studied about this the

more my conscience went to grinding me, and the

more wicked and low-down and ornery I got to feel-

ing. And at last, when it hit me all of a sudden that

here was the plain hand of Providence slapping me in

the face and letting me know my wickedness was being

watched all the time from up there in heaven,whilst I

was stealing a poor old woman's nigger that hadn't

ever done me no harm, and now was showing me

there's One that's always on the lookout, and ain't a-
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person goads, and crowds, and in a manner forces another person

to talk, it is neither very fair nor very good-mannered to call what

he says clack."



"Oh, snuffle--do! and break your heart, you poor thing. Somebody

fetch this sick doll a sugar-rag. Look you, Sir Jean de Metz, do you

feel absolutely certain about that thing?"



"What thing?"



"Why, that Jean and Pierre are going to take precedence of all the

lay noblesse hereabouts except the Duke d'Alenon?"



"I think there is not a doubt of it."



The Standard-Bearer was deep in thoughts and dreams a few

moments, then the silk-and-velvet expanse of his vast breast rose

and fell with a sigh, and he said:



"Dear, dear, what a lift it is! It just shows what luck can do. Well, I

don't care. I shouldn't care to be a painted accident--I shouldn't

value it. I am prouder to have climbed up to where I am just by

sheer natural merit than I would be to ride the very sun in the

zenith and have to reflect that I was nothing but a poor little

accident, and got shot up there out of somebody else's catapult. To

me, merit is everything--in fact, the only thing. All else is dross."



Just then the bugles blew the assembly, and that cut our talk short.



Chapter 25 At Last--Forward!



THE DAYS began to waste away--and nothing decided,nothing

done. The army was full of zeal, but it was also hungry. It got no

pay, the treasury was getting empty, it was becoming impossible to

feed it; under pressure of privation it began to fall apart and
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looking on in tears, all the way, enemies laughing. We reached

Gien at last--that place whence we had set out on our splendid

march toward Rheims less than three months before, with flags

flying, bands playing, the victory-flush of Patay glowing in our

faces, and the massed multitudes shouting and praising and giving

us godspeed. There was a dull rain falling now, the day was dark,

the heavens mourned, the spectators were few, we had no welcome

but the welcome of silence, and pity, and tears.



Then the King disbanded that noble army of heroes; it furled its

flags, it stored its arms: the disgrace of France was complete. La

Tremouille wore the victor's crown; Joan of Arc, the

unconquerable, was conquered.



Chapter 41 The Maid Will March No More



YES, IT was as I have said: Joan had Paris and France in her

grip,and the Hundred Years' War under her heel, and the King

made her open her fist and take away her foot.
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been disguised and set at lowly occupations for dramatic effect,

but I think McClintock is the first to send one of them to school.

Thus, in this book, you pass from wonder to wonder, through gardens

of hidden treasure, where giant streams bloom before you,

and behind you, and all around, and you feel as happy, and groggy,

and satisfied with your quart of mixed metaphor aboard as you would

if it had been mixed in a sample-room and delivered from a jug.



Now we come upon some more McClintockian surprise--a sweetheart

who is sprung upon us without any preparation, along with a name

for her which is even a little more of a surprise than she herself is.





In 1842 he entered the class, and made rapid progress in the English

and Latin departments.  Indeed, he continued advancing with such

rapidity that he was like to become the first in his class,

and made such unexpected progress, and was so studious, that he had

almost forgotten the pictured saint of his affections.  The fresh

wreaths of the pine and cypress had waited anxiously to drop once

more the dews of Heaven upon the heads of those who had so often

poured forth the tender emotions of their souls under its boughs.

He was aware of the pleasure that he had seen there.  So one evening ,as

he was returning from his reading, he concluded he would pay a visit

to this enchanting spot.  Little did he think of witnessing a shadow

of his former happiness, though no doubt he wished it might be so.
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In 1842 he entered the class, and made rapid progress in the English

and Latin departments.  Indeed, he continued advancing with such

rapidity that he was like to become the first in his class,

and made such unexpected progress, and was so studious, that he had

almost forgotten the pictured saint of his affections.  The fresh

wreaths of the pine and cypress had waited anxiously to drop once

more the dews of Heavens upon the heads of those who had so often

poured forth the tender emotions of their souls under its boughs.

He was aware of the pleasure that he had seen there.  So one evening,

as he was returning from his reading, he concluded he would pay a visit

to this enchanting spot.  Little did he think of witnessing a shadow

of his former happiness, though no doubt he wished it might be so.

He continued sauntering by the roadside, meditating on the past.

The nearer he approached the spot, the more anxious he became.

At the moment a tall female figure flitted across his path, with a

bunch of roses in her hand; her countenance showed uncommon vivacity,

with a resolute spirit; her ivory teeth already appeared as she

smiled beautifully, promenading--while her ringlets of hair dangled

unconsciously around her snowy neck.  Nothing was wanting to complete

her beauty.  The tinge of the rose was in full bloom upon her cheek;

the charms of sensibility and tenderness were always her associates..

In Ambulinia's bosom dwelt a noble soul--one that never faded--

one that never was conquered.  Her heart yielded to no feeling

but the love of Elfonzo, on whom she gazed with intense delight,

and to whom she felt herself more closely bound ,because he sought

the hand of no other.  Elfonzo was roused from his apparent reverie.

His books no longer were his inseparable companions--his thoughts

arrayed themselves to encourage him in the field of victory.
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that slavery was a bald, grotesque, and unwarranted ursurpation.  She had

never heard it assailed in any pulpit, but had heard it defended and

sanctified in a thousand.  As far as her experience went, the wise, the

good, and the holy were unanimous in the belief that slavery was right,

righteous, sacred, the peculiar pet of the Deity, and a condition which

the slave himself ought to be daily and nightly thankful for."



Yet Jane Clemens must have had qualms at times--vague, unassembled doubts

that troubled her spirit.  After Jennie was gone a little black chore-boy

was hired from his owner, who had bought him on the east shore of

Maryland and brought him to that remote Western village, far from family

and friends.



He was a cheery spirit in spite of that, and gentle, but very noisy.  All

day he went about singing, whistling, and whooping until his noise became

monotonous, maddening.  One day Little Sam said:



"Ma--[that was the Southern term]--,make Sandy stop singing all the

time.  It's awful."



Tears suddenly came into his mother's eyes.
================================================================================ Line 649,573 ===
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literati, local and visiting, used to gather there.  Names that would be

well known later were included in that little band.  Joaquin Miller

recalls from an old diary, kept by him then, having seen Adah Isaacs

Menken, Prentice Mulford, Bret Harte, Charles Warren Stoddard, Fitzhugh

Ludlow, Mark Twain, Orpheus C. Kerr, Artemus Ward, Gilbert Densmore,

W. S. Kendall, and Mrs. Hitchcock assembled there at one time.  The Era

office would seem to have been a sort of Mount Olympus, or Parnassus,

perhaps; for these were mainly poets, who had scarcely yet attained to

the dignity of gods.  Miller was hardly more than a youth then, and this

grand assemblage impressed him, as did the imposing appointments of the

place.



     The Era rooms were elegant--[he says]--,the most grandly carpeted

     and most gorgeously furnished that I have ever seen.  Even now in my

     memory they seem to have been simply palatial.  I have seen the

     world well since then--all of its splendors worth seeing--yet those
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================================================================================ END of file

As you can see, the second match stops at the first ,s, with an other string ,s, on the same line, not part of the second match

BR,

guy038

Coises

@guy038 said in Getting "Invalid Regular Expression" for an extremely simple expression:

At this point, I tried to select all the zones around these 11 matches in a small new file, that I named Matches.txt. Then, using the Mark dialog with (?:[^,]*,){13}[\u\l], against this small file, it does return 10 matches ( not 11 as explained in the next post ! )

However, it is distressing to note that the equivalent regex (?:.*?,){13}[\u\l] still fails against this tiny Matches.txt file, of only 16,138 bytes :-((

Unfortunately, it’s quite certain that cases, like that one, may arise when using most of the available regex engines !

There are two ways an implementation can look at a regex:

A regex is a definition of matching character strings.
A regex is a procedure for matching character strings.

From the first perspective, your two expressions are equivalent: they specify the same strings as matches. From the second perspective, they are not: they specify different procedures for finding strings that match.

No one has found a way to implement back references using method 1. Once your regular expression syntax includes the ability to use back references, you are stuck with the procedural interpretation.

There are other features of PERL-compatible regular expressions that present problems, but back references are the killer.

I’m speculating here, but I think once you include any back reference in an expression, it breaks the ability to process any part of the expression that occurs before the back reference as a definition rather than a procedure. (I’m not certain of that. I have no doubt someone does know the answer to that… but that someone isn’t me.)

So I think you’ll find all those more efficient regular expression engines implement a severely restricted syntax for regular expressions which omits features none of us would like to do without (particularly, back references).

What I’ve also speculated is that perhaps a regular expression engine could include two engines: one which processes using the ”definition” approach for expressions to which it is applicable, and one which uses the “procedural” approach for the remaining expressions. I don’t know if any do that now.