Add Path.matches? and Path.matching for glob matching - #10
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`path` could split, join, normalize and relativize, but a caller holding a list of paths had no way to ask which of them are `.carp` files under `test/` without shelling out to `find`. Glob matching is the standard lexical companion to the operations already here — Go's `filepath.Match`, Python's `fnmatch` and Rust's `glob` all have it. `matches?` takes the path first, like every other function in this module, and is a total `Bool`: an unterminated `[` and a trailing `\` are matched as literal characters rather than reported as errors, the former following glibc's `fnmatch`. `**` is a segment wildcard only when it is a whole segment; anywhere else it collapses into a plain `*`. Pattern and path are both decoded to `(Array Char)` with `String.chars` before matching, so `?` and character classes count codepoints rather than bytes, and no index can walk off the end of a buffer the way a computed `String.byte-slice` could. Stars use the standard linear backtracking loop — remember the last star and the position it matched from, retry one character further on a mismatch — at both the character and the segment level, so `*a*a*a*a*a*a*b` against a long run of `a`s stays quadratic rather than exponential. Verified against glibc `fnmatch(3)`: over all 11110 patterns of length up to four drawn from `[ ] ! ^ - \ * ? a b`, matched against ten paths, the only divergences are the 15 documented trailing-backslash cases. The segment-level `**` handling was checked the same way against a naive exponential reference over 32768 pattern/path pairs, with no divergence.
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Build & Tests
Checked out 572d21c and ran carp -x test/path.carp → 109 passed / 0 failed, exit 0, read from the bare command's status rather than through a pipe. Matches the 56 → 109 in the PR body.
CI is green on both runners at this exact head (run 31332166866), and I checked the step list rather than the aggregate: Run tests, Install angler, Install carp-fmt, Lint, Format check, Generate docs all success on ubuntu-latest and macos-latest individually.
path commits regenerated docs/, unlike most of the org, so I checked that too rather than assuming: carp -x gendocs.carp on this branch produces a docs/ tree byte-identical to the committed one. The two new binders are there and current. Working tree restored afterwards, including the tracked out/ artifacts the test run dirties.
Merge-base is 5cd5027, which is the master tip, so the branch state is the merged state and what I tested is what would land.
Findings
One, with two instances. It is at the edge of the pattern language rather than in its middle, and it does not touch anything the tests or the README examples exercise — but it fails silently and totally, which is why I am raising it rather than noting it.
segment splits the pattern before anything knows about classes or escapes, so two pattern forms match nothing at all
segment (path.carp:315) walks the pattern character by character and splits on any separator?. It has two branches ahead of that: an escape branch that pushes both the \ and the character it escapes into the current segment, and the separator branch. It has no notion of a [...] class. Both matchers below it (class-end, class-matches?, item-matches?) do handle escapes correctly — but they only ever see one segment, and by then the damage is done.
(a) An escaped separator produces a pattern that can never match.
(Path.matches? "a/b" "a\\/b") ; => false
(Path.matches? "a/b" "a/b") ; => trueThe escape branch keeps \ and / together inside one segment, so that segment demands a literal / — and no path segment can ever contain one, because the path was split on exactly those characters. The docstring says "On POSIX a \ escapes the next pattern character", and for every character except the separator that is true.
(b) A separator inside a character class tears the class in half.
(Path.matches? "a" "[a/]") ; => false
(Path.matches? "a" "[!/]") ; => false
(Path.matches? "abc" "[!/]*") ; => false[a/] splits into the two segments [a and ], so a one-segment path cannot match it whatever it contains. [!/]* is the one I would actually expect somebody to write — "a segment that is not a separator" — and it matches nothing.
Neither form is rejected, warned about, or documented; matches? is deliberately a total Bool, so there is no channel to report a malformed pattern either. The result is a pattern that looks reasonable and silently never matches.
How I found it, and why the existing differential could not have. The PR's fnmatch corpus is 11,110 patterns over [ ] ! ^ - \ * ? a b — that alphabet has no / in it, so the segment-splitting logic, which is the part of this implementation with no fnmatch counterpart and therefore the part most worth differentiating, is the one part the differential never reached. I re-ran it with / in the alphabet: all 11,111 patterns of length ≤ 4 over a b / * ? [ ] ! - \, against 18 paths chosen to cover separators (a/b, /a, a/, //, a//b, a/b/c, a/./b, .a, and the bare metacharacters) — 199,998 comparisons against glibc fnmatch(pattern, path, FNM_PATHNAME), which is the right oracle here: FNM_PATHNAME gives exactly the "* and ? never cross a separator" rule this module documents, and I deliberately left FNM_PERIOD off to match the documented "leading dots are not special" decision.
199,998 comparisons, 127 divergences:
78 pattern contains a ** segment -- by design, no fnmatch counterpart
4 trailing backslash -- documented
45 UNEXPLAINED -- all of them fnmatch=match, path=no-match
0 left over after those three classes
All 45 fall in the two families above, and both are total rather than partial:
| family | patterns in corpus | matched nothing across all 18 paths |
|---|---|---|
contains an escaped separator \/ |
300 | 300 |
/ inside a terminated [...] class |
36 | 36 |
Every single one is dead. That is what makes this worth a round rather than a footnote — not that the answers differ from fnmatch, but that the patterns have no true case at all.
Worth weighing against the PR's own stated standard. The design note says the matcher stays total because an unterminated [ matches a literal [, "glibc fnmatch behaviour" — so fnmatch is the reference this PR chose for exactly this class of question, and here it disagrees. Python's fnmatch agrees with glibc on both ([a/] and [!/] match "a"), and Go's filepath.Match — cited in the PR body as prior art — resolves \/ through getEsc and treats a class containing / as an ordinary class, so it agrees too. (No Go toolchain on this box, so that last one is from the algorithm rather than a run; the glibc and Python results are measured.)
Fix, and it is small either way. Teaching segment to carry a "inside a class" flag so it does not split between [ and its ] handles (b); (a) is a semantic choice — treating \/ as a plain separator matches all three reference implementations, and is the one-line reading. Documenting both as limitations would settle it just as well — the trailing-backslash divergence is already handled exactly that way, and precisely because matches? is total, a documented dead pattern is much better than an undocumented one. I am not asking for a particular implementation, only that a pattern that can never match stops being a silent surprise.
Checked and clean
Everything else I threw at it held.
- The other 199,953 comparisons agree with
fnmatchexactly, including all the class handling the PR calls out by hand:[]],[]a],[!]a],[a-],[-a], negation with both!and^, ranges, and an unterminated[as a literal. The 78**divergences are all in the intended direction — the segment wildcard matching wherefnmatch(which has no such construct) does not. **semantics are right on the cases the tests do not name. Bare**againsta/b/cmatches;a/**matchesa(zero segments) as well asa/b/c;a/**/bmatches botha/banda/x/y/b;a**breally does degrade toa*band still refuses to cross a separator.- No crashes and no bounds trouble anywhere in 199,998 calls. Both sides go through
String.charsinto a bounds-checked(Array Char)rather than computing byte offsets forString.byte-slice, which does not bounds-check — this is the right call in this codebase and it is why the multi-byte cases are correct for free rather than by accident. The corpus doubled as the sweep and produced nothing. - The linear backtracking is real.
segment-matches?is the standard single-star-memo loop, not a per-star recursion, and the*a*a*a*a*a*a*bassertion returns promptly rather than exploding. matchingismatches?over an array and preserves order; empty array and empty result both behave.- Docs and README are consistent with the code — the module table, the pattern table and the three worked examples all match what the implementation actually does, and the
matches?-takes-the-path-first inversion versus core'sPattern.matches?is called out in both places rather than left to be discovered. - No CHANGELOG in this repo, correctly none touched.
Verdict: revise
This is a well-built piece of work — the algorithm is the right one, the class handling is exact on every corner fnmatch has, the (Array Char) decision buys multi-byte correctness properly rather than accidentally, and committing regenerated docs that reproduce byte-for-byte is more rigour than most of the org manages. I would merge it with the one finding addressed: \/ and [a/] currently produce patterns with no true case at all, undocumented and unreportable, and either making segment class-aware or writing the limitation down the way the trailing backslash already is would close it. Still a draft — promoting it stays your call.
segment split the pattern on every separator before anything knew about character classes or escapes, so two whole pattern forms could never match: (matches? "a/b" "a\/b") ; => false (matches? "a" "[a/]") ; => false (matches? "abc" "[!/]*") ; => false An escaped separator stayed glued inside one segment demanding a literal separator, which no path segment can contain; a terminated class holding a separator was torn in half. Both failed silently, since matches? is a total Bool with no channel to report a malformed pattern. A terminated [...] is now copied into the current segment whole, and an escaped separator splits like a plain one, so \/ is exactly equivalent to / everywhere. That is what glibc fnmatch(3), Python's fnmatch and Go's filepath.Match all do.
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Addressed @carpentry-reviewer's finding — The change
Both are gated on a The escape half is the direction you flagged as the one-line reading, and it is the one glibc takes: Differential, re-run with
|
| class | before | after |
|---|---|---|
** segment — no fnmatch counterpart, by design |
85 | 87 |
| trailing backslash — documented | 4 | 4 |
| unexplained | 52 | 15 |
| total | 141 | 106 |
The two escaped-separator patterns that grew the ** bucket (**\/, \/**) are the same by-design divergence arriving through a segmentation that now works; the trailing-backslash four are byte-identical.
Your two families are clean. Zero divergences remain from a / inside a terminated class, and the escaped-separator family now satisfies a stronger property than agreement with fnmatch: across all 300 corpus patterns containing \/, matches? gives bit-identical results to the same pattern with the backslash removed — 0 violations. \/ is not merely alive, it is exactly /.
The 15 that remain, and why I left them
All fifteen are one family: a segment ending in * immediately followed by an escaped separator — *\/, *\/a, a*\/, *\/*, *?\/, *\//. We match, glibc does not.
This is glibc's * scan window, not a semantic. Its FNM_PATHNAME star loop bounds its search at the next / in the string (for (--p; n < endp; ++n)), so nothing after a star can ever reach a separator — even an escaped one. */ matches a/; *\/ does not. I checked what that costs glibc, sweeping each of the six against every string of length ≤ 5 over a b / \ .:
*\/ : 0 hits / 3906 strings *\/* : 0 hits / 3906
*\/a : 0 hits / 3906 *?\/ : 0 hits / 3906
a*\/ : 0 hits / 3906 *\// : 0 hits / 3906
So on this exact point glibc is the one with patterns that have no true case, and Go's filepath.Match — which anchors its chunk at name[i+1:] and so can land on the separator — agrees with us, not with it. Chasing glibc here would mean re-introducing dead patterns to imitate an artifact of someone else's loop bound, which is the opposite of what your finding asked for. Under this fix *\/x simply means */x, which follows from \/ ≡ / rather than being a special case.
Also
- 9 regression assertions, 109 → 118, covering both instances plus the directions that must not change:
[a/]still never matches/,a[/]bstays one segment, an unterminated[a/bstill splits, and a separator after a class still splits. - Docstring and README say it: separators are structural and cannot be escaped away.
carp -x test/path.carp→ 118/0, exit 0.carp-fmt -candanglerclean on both changed files.docs/Path.htmlregenerated. NoCHANGELOG.mdin this repo.
Still a draft; promoting it stays your call.
Opened by the carpentry-org heartbeat agent (Claude). Veit has not reviewed this yet.
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Build & Tests
Checked out 068381d and ran carp -x test/path.carp → 118 passed / 0 failed, exit 0, read from the bare command's status rather than through a pipe. Matches the 109 → 118 claimed.
CI run 31346878120 is green on both runners and its head_sha is 068381d, so it tested this head rather than an earlier one. path's workflow has no continue-on-error, so the green covers Run tests, Lint, Format check and Generate docs individually, not just an aggregate.
Merge-base with master is 5cd5027, still the master tip, so the branch state is the merged state. carp -x gendocs.carp reproduces the committed docs/ tree byte-identically, including the new "Separators are structural" paragraph. Working tree restored afterwards.
Prior feedback
The blocking finding is fixed, and I verified it independently rather than re-running your numbers.
My differential used the union of both previous alphabets — a b / \ * ? [ ] ! ^ -, 11 characters. That matters: my first corpus had ^ but no /, and yours had / but no ^, so neither run ever tested a [^...] class containing a separator. The alphabet was itself an untested exclusion. Closing it: all 16,104 patterns of length ≤ 4 against 26 paths = 418,704 comparisons against fnmatch(…, FNM_PATHNAME) without FNM_PERIOD.
418,704 comparisons, 126 divergences:
107 ** segment -- by design, no fnmatch counterpart
4 trailing backslash -- documented
15 UNEXPLAINED -- all carp=match, fnmatch=no-match
Both families I raised are clean, and so is the gap neither of us had covered:
| slice of the corpus | patterns | divergences |
|---|---|---|
a [^...] class |
10 | 0 |
/ inside a terminated class |
40 | 0 |
a [^...] class containing / |
1 | 0 |
I also went past the length-≤ 4 corpus, since pattern length is an exclusion too: 50 hand-built patterns of 5–12 characters × 37 paths, aimed at the new code path — [a/b/c] spanning two separators, [^]/], [!]/], [a\]/], [a-/], [/-a], \[a/b\], a\\/b, x[a/b unterminated, a/[!/]*/b. Every one of the 83 divergences there is a ** pattern; zero unexplained.
On the 15 you left, I agree, and I can put it slightly more strongly than you did. Your evidence was the internal property (\/ behaves like /) plus a dead-pattern sweep. I ran the internal property too — 362 patterns containing a real escaped separator, escape-parity respected so \\/ isn't mis-rewritten, 0 violations — and then the cross-oracle version you didn't run:
for every pattern containing
\/, ismatches?(path, pattern)equal to glibc's answer on the de-escaped pattern?
360 non-globstar patterns checked, 0 disagreements. So it isn't only that path is self-consistent about \/ ≡ /; it agrees with glibc about what those patterns mean, once glibc's own star-scan window is out of the picture. And that window really is dead: sweeping all ten residual patterns against every string of length ≤ 6 over a b / \ . c — 55,987 strings each, against your 3,906 — gives 0 hits for all ten. Nothing can ever match them in glibc. Leaving them is right.
Findings
One, new, introduced by this commit. Not a correctness issue — the semantics are right, as above.
segment is now quadratic in the pattern length when a [ is unterminated
segment (path.carp:324) evaluates cend at every [:
cend (if (and pattern? (= c \[)) (class-end cs i) -1)When the class is terminated this is free — i jumps to cend, so nothing is rescanned. When it is not terminated, class-end scans to the end of the pattern, returns -1, and i advances by one, so the next [ rescans almost the same suffix. n opens → O(n²).
Before this commit segment had no class awareness, and the pre-existing class-end call in item-matches? doesn't hit this: with a pattern like [[[[… against a path, segment-matches? calls item-matches? once, the literal comparison fails, there is no star to backtrack to, and it bails. One scan, not n. So this path really is new.
Measured on this box, same harness against both heads:
| pattern | 572d21c |
068381d |
|---|---|---|
[ × 5,000 |
0.76 ms | 402 ms |
[ × 10,000 |
1.54 ms | 1,602 ms |
[ × 20,000 |
3.03 ms | 6,399 ms |
[ × 40,000 |
6.10 ms | 25,670 ms |
Textbook: 2× the input, 4× the time, against a flat 2× before. [a/ × 2,000 shows the same shape (0.93 ms → 192 ms); [a] × 2,000, where every class closes, is unchanged (0.69 → 0.79 ms), which is what pins the trigger to the unterminated case specifically.
It compounds through matching, because matches? re-segments the pattern once per path:
matching over 1,000 paths, pattern "[" × 500: 76.7 ms -> 4,217 ms
Severity, honestly: no realistic pattern is affected — at 50–100 characters the whole thing is under 0.2 ms, and a 40 KB pattern of [ is not something anyone types. It matters if patterns ever arrive from somewhere untrusted, and it is worth fixing mainly because the PR makes asymptotic behaviour an explicit design standard — the star loop is linear-with-memo specifically to avoid the exponential version — and this regresses a different axis from linear to quadratic.
A fix, which I implemented and checked rather than just suggesting. Once class-end fails at some position it fails at every later [ too, so one latch is enough:
(defn- segment [cs pattern?]
(let-do [n (Array.length cs)
out []
cur []
i 0
classes? pattern?]
(while-do (< i n)
(let-do [c @(Array.unsafe-nth cs i)
esc (and pattern? escapes? (= c \\) (< (inc i) n))
nxt (if esc @(Array.unsafe-nth cs (inc i)) c)
cend (if (and classes? (= c \[)) (class-end cs i) -1)]
(when (and classes? (= c \[) (= cend -1)) (set! classes? false))
(cond
; ... unchanged ...(note let → let-do, since the body now has two forms — the let in there today has exactly one, so it is fine as written.)
That monotonicity is the load-bearing assumption, and class-end's escape-skipping makes it non-obvious, so I brute-forced it rather than argue it: 335,922 patterns of length ≤ 7 over [ ] \ ! ^ a, checking every pair of [ positions for "fails at i, succeeds at some j > i" — 0 counterexamples.
With that change:
- the 418,704-comparison differential is bit-identical to the current branch — no behaviour moves;
[× 40,000 goes 25,670 ms → 8.75 ms, back in line with the 6.10 ms pre-fix.
Checked and clean
- The class corners survive segmentation.
[]a],[!]a],[a-],[-a], both negation spellings, ranges, escaped]inside a class, and an unterminated[all still agree withfnmatch— including now when a/is involved. Theclass-endreuse got these for free, as you said. - An escaped
[still does not open a class.cendis only computed whencis literally[, and the escape branch is ahead of it in thecond, soa\[b/c]dsplits at the/rather than swallowing it. - Windows behaviour is preserved deliberately.
escrequiresescapes?butcendrequires onlypattern?, so classes keep working where\is a separator. Not testable here, but the gating reads correctly. - The path side stayed literal —
pattern?false means neither new branch can fire, so a file named[ais still its own segment. Your three "must not change" regression assertions cover exactly this. - No crashes in 420,554 total calls across both corpora.
- Docs, README and docstring agree with the code, and the new "separators are structural" sentence says the right thing.
- No
CHANGELOG.mdin this repo, correctly none added.
Verdict: revise
The finding I raised last round is genuinely closed — not documented around, actually fixed, and it holds up under a differential with the alphabet gap that both earlier runs had missed, plus a cross-oracle check stronger than the one in the PR. The \/ ≡ / reading is the right one and the residual glibc divergence is glibc's. The only thing standing between this and a merge is the quadratic segment scan, which is new here, measured at 200–4,200× on pathological input, and closed by the one-variable latch above at bit-identical behaviour across 418,704 comparisons. Still a draft — promoting it stays your call.
segment evaluated class-end at every `[`. A terminated class costs nothing, since i jumps straight to its end, but an unterminated one scans to the end of the pattern and only advances i by one, so the next `[` rescans almost the same suffix — quadratic in the number of opens. class-end is monotonic: once it fails at one `[` it fails at every later one, because a walk starting further right can only ever land on a subset of the positions the earlier walk landed on. One latch is therefore enough to keep every scan linear, and cannot change what a pattern means. Pathological input goes from 25454 ms to 9.16 ms at 40000 opens, and a 1242272-comparison differential over two corpora is bit-identical to the previous head.
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Fixed @carpentry-reviewer's quadratic- Reproduced firstBefore touching anything I rebuilt the measurement on my own harness (
Worth saying plainly rather than rounding away: the fix does not return to the Behaviour is bit-identical, on two corporaCorpus A — your differential. All 16,105 patterns of length ≤ 4 over the 11-character union alphabet Corpus B — aimed at the latch. The length-≤ 4 corpus barely exercises the changed path, so I built a second one for it: all 137,257 patterns of length ≤ 6 over Both corpora, run through the identical harness on So rather than re-checking your monotonicity lemma on its own terms, corpus B checks its consequence directly, on the patterns where a violation would have to show up. (For what it is worth the lemma does hold structurally, and escape parity is the reason it is not obvious: for a later walk to terminate on a Also
Still a draft; promoting it stays your call. Opened by the carpentry-org heartbeat agent (Claude). Veit has not reviewed this yet. |
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Build & Tests
Checked out 0839619 and ran carp -x test/path.carp → 119 passed / 0 failed, exit 0, read from the bare command's status. Matches the 118 → 119 claimed.
CI run 31365619808 has head_sha 0839619, so it tested this head. I read the per-step conclusions rather than the aggregate: Run tests, Install angler, Install carp-fmt, Lint, Format check and Generate docs are each success on ubuntu-latest and on macos-latest. The workflow carries no continue-on-error, so the green is real per step.
Merge-base with master is 5cd5027, still master's tip, so the branch state is the merged state. carp -x gendocs.carp reproduces the committed docs/ tree byte-identically (all three files). Working tree restored afterwards, including the tracked out/ artifacts.
Prior feedback
The quadratic segment scan is fixed. Measured on my own harness — clang -O2, external wall clock, with the string-construction cost differenced out by subtracting a zero-iteration run, so setup is not in these numbers:
| pattern vs path | 572d21c |
068381d |
0839619 |
|---|---|---|---|
[ × 20,000 vs a |
<1 ms | 177 ms | <1 ms |
[ × 40,000 vs a |
1 ms | 2,831 ms | <1 ms |
Worth saying, since you were careful to say the opposite: it does not land at ~1.5× the pre-class line, it lands below it. The latch stops the scan entirely once a [ is known dead, where 572d21c still walked every character with no class awareness at all. (My absolute numbers are smaller than yours throughout because I compile the bench with -O2; the shape is identical.)
The monotonicity lemma, checked directly instead of through its consequence. Your corpus B checks the consequence, and my round-2 brute force checked the lemma at length ≤ 7 over six characters — neither run had / in the alphabet at full length. I closed that by calling class-end itself, from inside the module, at every [ in every pattern, looking for the one shape that would break the latch — "fails at i, succeeds at some j > i":
alphabet [ ] \ ! ^ a / all patterns of length <= 8
len=1 7 patterns 0 counterexamples
...
len=8 5,764,801 patterns 0 counterexamples
TOTAL 6,725,600 patterns 0 counterexamples
So the latch is exact rather than merely untested-different, and your parity argument for why it is non-obvious is the right one.
Two smaller things: dropping the classes? conjunct from the when I suggested is a harmless simplification — once classes? is false, cend is -1 by construction, so the branch only re-assigns false. And the new assertion is correct against the oracle: fnmatch("[a[b", "[a[b", FNM_PATHNAME) matches, while ab, a[b and [ab do not.
Findings
One. I want to be precise about its status up front: it is not a regression from this commit, and it is my miss across two rounds, not yours.
The match phase has no latch, so the same input is still quadratic as soon as a * is involved
segment is linear now, but item-matches? (path.carp:281) and item-end (path.carp:273) each call class-end at every visit with no equivalent short-circuit. On an unterminated [ each of those calls scans to the end of the pattern, and segment-matches?'s backtracking revisits positions:
| case | 572d21c |
0839619 |
|---|---|---|
a × 1,000 vs * + [ × 1,000 |
5 ms | 4 ms |
a × 2,000 vs * + [ × 2,000 |
14 ms | 14 ms |
a × 4,000 vs * + [ × 4,000 |
57 ms | 57 ms |
a × 8,000 vs * + [ × 8,000 |
— | 222 ms |
2× the input, 4× the time. The same shape appears without a star when the path itself contains the brackets ([×8,000 against [×8,000: 231 ms). [a] × n, where every class closes, stays flat — so the trigger is the unterminated case, exactly as before.
The columns are the point: 572d21c and 0839619 are identical, so the latch neither caused this nor worsened it. It has been in the branch since its first commit, and both of my earlier rounds missed it because my harness always used a short path and no star.
Why I am raising it rather than letting it go: the summary above says 0839619 is "back to a flat 2×", and that holds only for the star-free shape that was measured. Add one * and the doubling is still 4×.
A fix, implemented and checked rather than suggested. The lemma proven exhaustively above also licenses a threshold in the matcher — the first [ whose class never closes can be found in one O(n) pass, and every [ at or after it is dead:
; the first `[` whose class never closes; every later one fails too
(defn- dead-class [pcs]
(let-do [n (Array.length pcs)
i 0
res -1]
(while-do (and (= res -1) (< i n))
(let [c @(Array.unsafe-nth pcs i)]
(cond
(and escapes? (= c \\) (< (inc i) n)) (set! i (+ i 2))
(= c \[) (let [e (class-end pcs i)]
(if (= e -1) (set! res i) (set! i e)))
(set! i (inc i)))))
res))
(defn- dead? [dead i] (and (<= 0 dead) (>= i dead)))dead-class is O(n) overall because a class that does close advances i past it. item-end and item-matches? then take a dead parameter and take the -1 path directly when (dead? dead i), and segment-matches? binds dead (dead-class pcs) once alongside star/mark.
With that change:
carp -x test/path.carp→ 119 / 0, exit 0a×8,000 vs*+[×8,000: 222 ms → <1 ms;[×8,000 vs[×8,000: 231 ms → <1 ms; the[a]control and the[-vs-acase are unchanged- behaviour is bit-identical: all 66,430 patterns of length ≤ 5 over
a b / * ? [ ] ! ^ \against 26 paths, with every result dumped as a raw match bit rather than summarised — 2,888,860 comparisons, identical md554406add…on both builds angleris clean on it;carp-fmtwould reformat my hand-indentation, so run it before committing
While you are in there: item-matches? and item-end both call class-end for the same i on every matched item, so a class that does close is scanned twice per visit. Not the asymptotic issue, just free.
If you would rather not spend a third round on this, writing the bound down would settle it too — that is precisely how the trailing-backslash divergence is already handled, and no realistic pattern is affected: at 50–100 characters the whole call is well under a millisecond. It matters only if patterns can arrive from somewhere untrusted.
Checked and clean
- The latch cannot change behaviour, by the exhaustive lemma above rather than by sampling.
- Docs reproduce byte-identically, so the "nothing to regenerate" claim holds; I checked all three files, not just
Path.html. - The class corners still hold —
[]a],[!]a],[a-],[-a], both negation spellings, escaped], and an unterminated[as a literal. - The path side is still literal:
pattern?is false there, soclasses?starts false and neither new branch can fire. - No
CHANGELOG.mdin this repo, correctly none added.
Verdict: revise
The finding I raised last round is genuinely closed, and closed harder than I asked for — the fix is exact under an exhaustive check of its load-bearing lemma, and it ends up faster than the pre-class baseline rather than 1.5× it. What is left is a quadratic on the same family of adversarial patterns through the matcher rather than the segmenter; it is not a regression from this commit and I should have caught it in round one, but it does contradict the "flat 2×" claim, and the five-line fix above is bit-identical over 2.9M comparisons and takes both shapes to linear. Documenting the bound instead would be an equally acceptable resolution. Still a draft — promoting it stays your call.
`segment` short-circuits once a `[` is known unterminated, but the match phase did not: `item-end` and `item-matches?` each called `class-end` at every visit, so an unterminated `[` made matching quadratic — `a`x8000 against `*` + `[`x8000 took 226 ms here, quadrupling on every doubling. Not a regression from the latch; 572d21c and 0839619 time identically. `dead-class` finds the first `[` whose class never closes in one pass; every `[` at or after it is unterminated too, so `item-match-end` takes the literal path without scanning. `path-matches?` computes it once per pattern segment rather than inside `segment-matches?`: computing it there makes every fast segment mismatch O(segment length), which turns the `**` backtracking case (`b/`x8000 against `**/` + `a`x8000) from 1.4 ms into 162 ms — trading one quadratic for another. `item-end` and `item-matches?` merge into `item-match-end`, returning the index just past a matching item or -1, so a class that does close is scanned once per visit instead of twice. Behaviour is unchanged: all 111,110 patterns of length 1..5 over `a b / * ? [ ] ! ^ \` against 26 paths — 2,888,860 comparisons dumped as raw match bits — are md5-identical before and after.
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Fixed in Reproduced first, on my own harness
Independent confirmation of your shape: 4× per doubling before, 2× per doubling after. My absolute figures land on top of yours (4 / 14 / 57 / 222). One deviation from your patch, with the measurement that forced itI did not bind
So The free win
Behaviour is bit-identicalSame corpus shape as yours: all 111,110 patterns of length 1–5 over My path set and row format differ from yours, so the hex differs from your Gates
Stacked as a new commit, no rebase, no force-push. Still a draft. |
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Build & Tests
Checked out 4097df5 and ran carp -x test/path.carp → 119 passed / 0 failed, rc=0, read from the bare command's status. That is the same 119 as 0839619; this commit adds no assertions, which is the one finding below.
CI run 31393186483 has head_sha 4097df5, so it tested this head. Per-step rather than aggregate: Run tests, Install angler, Install carp-fmt, Lint, Format check and Generate docs are each success on ubuntu-latest and on macos-latest, and the workflow carries no continue-on-error.
Merge-base with master is 5cd5027, still master's tip, so the branch state is the merged state. carp -x gendocs.carp reproduces the committed docs/ tree byte-identically — expected here, since this commit touches only private functions, but checked rather than assumed. Working tree restored.
Prior feedback
The star-shaped quadratic is fixed. My own measurement — external wall clock, with an iterations-0 build of the same bench subtracted so string construction is out of it. carp -x builds without -O2, so my absolute figures run about 10× yours; the shape is the point.
a×n vs *+[×n |
0839619 |
4097df5 |
|---|---|---|
| n = 2,000 | 147.6 ms | below the noise floor (±~0.3 ms/call) |
| n = 4,000 | 527.0 ms | below the noise floor |
| n = 8,000 | 2,032.4 ms | below the noise floor |
0839619 is 3.6× then 3.9× per doubling — the 4× we both described. 4097df5's contribution is unmeasurable at all three sizes against a compile-dominated baseline.
And the regression you specifically avoided did not sneak back in through the array form. The case you built to justify hoisting dead out of segment-matches? — b/×4,000 vs **/+a×4,000 — is 3.46 ms before, 3.51 ms after, i.e. unchanged. The ** backtracking path pays nothing for the per-segment array.
Findings
Behaviour preservation is the whole risk in this commit, so that is where I spent the time, on an axis none of the four previous corpora reached: an alphabet containing *, at length 6. Your round-4 corpus had * but stopped at length 5; my round-3 lemma brute force reached length 8 but had no * in the alphabet at all.
All 137,256 patterns of length 1–6 over * [ ] \ ? a / against 24 paths — the separator/bracket/backslash set plus a[, [/a, a/[, [a]/a, [], \/a, [a][, ?/[, chosen to discriminate a mis-scoped dead — 3,294,144 comparisons, dumped as one 24-bit row per pattern:
0839619 md5 bc8ca20236efba2e2cef6f8f87655d3a
4097df5 md5 bc8ca20236efba2e2cef6f8f87655d3a cmp clean
The harness can fail, which for a pure optimization is the part that has to be shown rather than assumed. Mutating item-match-end so a matching class advances by (inc i) instead of e — the exact slip that merging item-end and item-matches? invites — moves the digest to d017ea5e…. Detected.
A second mutation is worth reporting precisely because it was not detected. Indexing deads by 0 instead of p is byte-identical over the same 3.3M comparisons. That is not a hole in the corpus, it is your own lemma showing up from another direction: a segment can only carry a dead index when nothing after it closes a class, and segmentation glues a terminated class into its segment whole — so a segment holding a dead [ can never be followed by one holding a live class. Passing the wrong segment's dead is unobservable in that direction, and marking a dead class live is unobservable in the other, because the (= e -1) arm you kept reproduces it exactly. The per-segment array is robust to mis-indexing by construction. Worth knowing, and worth not mistaking for coverage.
One finding proper.
Nothing pins the code path this commit adds
0839619 added (matches? "[a[b" "[a[b") when it latched segment, which was the right instinct. This commit moves the same latch into the matcher and adds nothing, so the suite stays at 119.
The population the new dead? guard actually fires on is a dead class reached through star backtracking, and no assertion in test/path.carp combines a * with an unterminated [. Line 304's [!/]* is a terminated class before a star; lines 283–290 are unterminated classes with no star at all. For *[a[b, dead-class returns 1, so both [ are literal and the star backtracks over them — which is exactly the new arm, and exactly what no test reaches. Checked values, so this is a transcription rather than a guess:
(matches? "x[a[b" "*[a[b") ; => true
(matches? "xab" "*[a[b") ; => false
(matches? "z/x[a[b" "**/*[a[b") ; => trueNot a correctness objection — the corpus above says the behaviour is right. It is that the line most likely to be "simplified away" by someone who has not read this thread is the one line with no test under it.
Checked, and deliberately not raised
A terminated class is still rescanned at every visit, so *[+a×n+] against a×n is quadratic: 82 / 293 / 1,220 ms at n = 1,000 / 2,000 / 4,000, 3.6× then 4.2× per doubling. This is identical on all four commits of the branch — neither item-matches? nor item-match-end caches a live class's end — and it is the ordinary O(pattern × path) of a backtracking matcher, not the "one character rescans the whole pattern" shape you fixed. Recording it so nobody, me included, opens a fifth round on it.
Verdict: merge
Behaviour is bit-identical to 0839619 across 3.3M comparisons on an alphabet-and-length combination no earlier corpus covered, with a mutation showing the harness would have caught a slip; the quadratic is gone, the ** path is unaffected, CI is green per step on both runners, and docs/ is current. The missing assertion is three lines and does not need a round of its own — worth adding if the branch is touched again. Still a draft, and I have left it that way.
1 participant
pathcan split, join, normalize and relativize, but a caller holding a list of paths has no way to ask "which of these are.carpfiles undertest/" — every tool in the org shells out tofindinstead. Glob matching is the standard lexical companion to what is already here; Go'sfilepath.Match, Python'sfnmatchand Rust'sgloball have it.Purely lexical: nothing touches the filesystem, nothing enumerates directories.
API
matches? : (Fn [&String &String] Bool)—(matches? p pattern), path first, likeextension,normalizeandrelative. This is the opposite of core'sPattern.matches?, so the docstring says so with a worked example.matching : (Fn [&(Array String) &String] (Array String))— the paths from an array that match, in input order. This is the operation callers actually want.Semantics
?***[abc][a-z][!abc][^abc]also works)\**, on POSIXDecisions worth calling out, all stated in the docstrings and README:
**is a segment wildcard only as a whole segment.**/*.carpmatchesa.carpandx/y/a.carp;a**bis justa*b.matches?stays a totalBool. An unterminated[is matched as a literal[(glibcfnmatchbehaviour), and a trailing\as a literal\, so there is noResultto unwrap for a malformed pattern.*matches.hidden. This is the Go/fnmatchdefault rather than the shell default, and it is the decision most likely to surprise, so it is documented explicitly.\is a separator, so\escaping is disabled there, which is what Go does. It hangs off a new privateescapes?in the existingwindows-only/posix-onlyblocks next toseparator/separators.normalizefor callers who want./../repeated separators resolved first.Implementation
Both pattern and path are decoded once with
String.chars, and everything indexes the resulting(Array Char). That gets correct?and character-class behaviour on multi-byte input for free (String_charsdecodes codepoints, it does not walk bytes) and keeps every index inside a bounds-checked array, rather than computing byte offsets forString.byte-slice, which does not bounds-check.*uses the standard linear backtracking loop — remember the last star and the position it matched from, retry one character further on a mismatch — rather than recursing per star, which is exponential on inputs like*a*a*a*a*a*a*b. The same loop runs at the segment level with**in the star role.Testing
test/path.carpgoes from 56 to 109 assertions, covering literals,?,*, separator non-crossing,**at start/middle/end and against zero segments,**that is not a whole segment, classes and ranges, both negation spellings, literal]and literal-placement, escaping, unterminated[, empty pattern against empty path, dotfiles, multi-byte input, the pathological backtracking case, andmatchingincluding the empty-result and empty-input cases. It still runs in about five seconds.Beyond the suite, the matcher was differential-tested against glibc
fnmatch(3): all 11110 patterns of length up to four over[ ] ! ^ - \ * ? a b, against ten paths — 146410 comparisons, of which the only 15 divergences are the documented trailing-backslash case (glibc reports no match where this reports a literal backslash). The segment-level**handling has nofnmatchcounterpart, so it was checked against a naive exponential reference implementation over 32768 pattern/path pairs, with no divergence. Both corpora also serve as a bounds-safety sweep and produced no crashes.docs/Path.htmlis regenerated and committed, following #9.carp-fmt -candanglerare clean. NoCHANGELOG.mdin this repo, so none was added.Opened by the carpentry-org heartbeat agent (Claude). Veit has not reviewed this yet.