Claude Haiku 5.5 (effort default (no --effort flag) · thinking on) on Make an ignore-file pattern matcher follow its spec (anchoring, directory-only, double-star, negation, parent exclusion)

AClaude Haiku 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-20 · by @bobsiopener

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Estimated cost: $0.03
Wall time: 3m
Human step-ins: 0
Outcome: Pass

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Exact prompt

# Make the ignore-file matcher follow its spec `ignore.py` decides which paths our sync tool skips, using `.gitignore`-style patterns. It is a quick `fnmatch` hack and gets many cases wrong. Rewrite it so `Matcher(text).ignored(path, is_dir=False)` follows the rules below exactly. Python 3 standard library only. Keep the class name, constructor and method signature. `path` is a relative POSIX path with no leading `./` or `/` (e.g. `src/app/main.py`); `is_dir` says whether the path itself is a directory. Every ancestor of `path` (e.g. `src`, `src/app`) is a directory. ## Rules 1. **Lines.** Split `text` into lines (strip a trailing `\r`). Trailing spaces are removed unless the last space is escaped as `\ ` (backslash-space, which keeps one literal space). Blank lines are ignored. A line starting with `#` is a comment; `\#` at the start is a literal `#`. Leading spaces are NOT stripped. 2. **Negation.** A leading `!` makes the pattern a negation (re-include). `\!` at the start is a literal `!`. 3. **Directory-only.** A trailing `/` is removed and makes the pattern match only directories. A pattern that is empty after removing `!` and the trailing `/` is ignored. 4. **Anchoring.** If the remaining pattern contains a `/` anywhere (start or middle), it is matched against the full path from the root (a leading `/` is dropped first). Otherwise it is matched against the last component at any depth (i.e. against the full path or any suffix that starts right after a `/`). 5. **Wildcards.** `*` matches any run of characters except `/` (including none); `?` matches exactly one character except `/`. `[...]` is a character class: ranges like `a-z` work, `!` or `^` as the first character negates it, a `]` directly after `[` (or after the negation mark) is literal; a class never matches `/`. A `[` with no closing `]` is a literal `[`. A backslash outside a class makes the next character literal. 6. **Double star.** Only these forms are special: a leading `**/` matches zero or more leading directories; `/**/` matches one `/` or `/any/dirs/`; a trailing `/**` matches one or more characters (anything inside, but not the directory itself). Any other run of `*` (e.g. `a**b`, `**` on its own) behaves like a single `*`. 7. **Last match wins.** For a given path, look at all patterns in file order; the last one that matches decides (normal = ignored, negated = not ignored). No match = not ignored. Directory-only patterns are only considered when the path being tested is a directory. 8. **Parents.** First test each ancestor directory from the top (`src`, then `src/app`, ...) using rule 7 with `is_dir=True`. If any ancestor is ignored, the path is ignored and nothing (not even a later `!` pattern) can re-include it. Otherwise the path's own result from rule 7 is the answer. 9. **Speed.** Building a matcher from 300 patterns and answering 20,000 `ignored()` calls must take under 10 seconds in total on our (shared, slow) test box. ## Scoring Hidden checks (one per group, all must pass; partial credit is the fraction passed): `comments_spaces_escapes` (rules 1-2, 5 backslash), `negation_last_match` (2, 7), `dir_only` (3, 7), `anchoring` (4), `wildcards_classes` (5), `double_star` (6), `parent_exclusion` (8), `randomized_agreement` (400 random pattern/path pairs built from the characters `a b / * ? [ ] ! -` must all agree with the rules), `speed` (9). Each group has 10-40 exact assertions.

Nine interacting rules (escaped trailing spaces, class edge cases like []] and [!]], three special ** forms, last-match-wins, and 'a parent directory once excluded cannot be re-included') checked by exact assertions plus 400 randomized pattern/path pairs, so half-right regex translations score partially. Original benchmark task written for usecaserank.com (not based on a specific public post). Headless, offline run on a reproducible fixture. Each run's notes say how its cost was measured (estimates are marked).

Success criteria: 1. comments_spaces_escapes 2. negation_last_match 3. dir_only 4. anchoring 5. wildcards_classes 6. double_star 7. parent_exclusion 8. randomized_agreement (400 random pairs) 9. speed (300 patterns x 20,000 paths < 10 s)

Setup notes: Use Case Scout batch 8 case i01-gitignore-matcher (offline fixture). Prepared with batch8/prepare.sh; hidden key/tests kept outside the agent's work dir. Prompt = TASK.md verbatim. Scored with the scout's scorer: `python score.py WORKDIR KEYDIR`. Tools: Read/Write/Edit/Glob/Grep/Bash, web disabled. Single run, no retries. 1-min load average at scoring: 2.06. Claude Code's own reported cost for claude-haiku-5.5: $0.027221. Score: 9/9. Cost is an ESTIMATE: measured tokens x pricing.json list price (Claude Pro subscription, nothing billed); input_tokens include cache reads and writes. Single run.

Estimated cost List-price estimate; not actually billed.

Metrics

Estimated cost: $0.03
Wall time: 3m
Human step-ins: 0
Turns: 6

Model usage
Model	Input tok	Output tok	Cost
AClaude Haiku 5.5anthropic/claude-haiku-5.5effort default (no --effort flag) · thinking on	222,477	33,854	$0.03

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Haiku 5.5 (anthropic/claude-haiku-5.5, effort default (no --effort flag) · thinking on) via Claude Code 2.1.299 (headless -p), cloud.
It counts as a success only if it meets every success criterion: 1. comments_spaces_escapes 2. negation_last_match 3. dir_only 4. anchoring 5. wildcards_classes 6. double_star 7. parent_exclusion 8. randomized_agreement (400 random pairs) 9. speed (300 patterns x 20,000 paths < 10 s)
Log model, tokens, wall time, human step-ins and the evidence log, then submit it as a reproduction. A different model? Submit a head-to-head rerun.

How runs are scored: Methodology.

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Automated checks

Trust 80% comes from these checks (how Trust % works).

Run date is not in the future : passed
Model is in the dated pricing table : passed
Cost recomputed from tokens matches : passed
Cached tokens are consistent : passed
Output throughput is plausible : passed
Autonomy matches step-ins : passed
Step-ins do not exceed turns : passed
Retries agree with first-try result : passed
Evidence log SHA-256 matches : passed
Evidence log is substantial : passed

Evidence log

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  "result": "I rewrote `ignore.py` so `Matcher(text).ignored(path, is_dir=False)` follows the rules in `TASK.md`. The class name, constructor and method signature are unchanged, and it uses only the standard library. My scratch checks pass: 0 failures across about 60 hand-worked cases covering every rule group, and 20,000 calls against 300 random patterns ran in 0.01 s.\n\nThe old file cited `IGNORE_SPEC.md`, which isn't in the directory, so I took `TASK.md` as the spec.\n\n**How it works**\n- Each pattern is translated once into a regex. Patterns are grouped by anchored and directory-only, and each group is one alternation ordered last-to-first, so the first hit is the last matching rule (rule 7).\n- Directory results are cached, so ancestor checks (rule 8) don't repeat work.\n\n**Edge cases the spec didn't settle, where I chose:**\n- Only one trailing `/` is removed, so `foo//` stays anchored and effectively matches nothing.\n- `/**` after the leading slash is dropped is treated as a single `*`, so `/**` only matches top-level names.\n- Consecutive `**/` runs collapse into one.\n- A lone trailing backslash matches a literal backslash.\n- Unclosed `[` is a literal `[`.\n- Ranges with the low end above the high end match nothing.\n- Classes never match `/`, including `[/]` and negated classes.\n\nI have no reference implementation to run the 400-pair randomized check against, so that group's pass/fail is unverified. The random patterns only use `a b / * ? [ ] ! -`, so they mostly exercise the single-star, class and negation paths, which my checks covered.\n\nThe file is at `./usecase-runner/runs/i01-claude-haiku/work/ignore.py`. The directory isn't a git repo, so I did not commit anything.",
  "ttft_ms": 1246,
  "type": "result",
  "duration_ms": 151187,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 1067,
  "time_to_request_ms": 244,
  "first_content_frame_ms": 1068,
  "queued_turn_count": 0,
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 }
]