HermitCrab analysis can spin on simultaneous rewrites with incompatible environments

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Dal 9/11/2026.

  • #624 di @johnml1135 — aperta

Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
58/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
csharp
Ambito
backend, testing-qa

Direzione di ricerca

Start with AnalysisRewriteRule.cs around the SelfOpaquing selection and reapplication loop, then inspect SimultaneousPhonologicalPatternRule.cs and its no-match behavior. Add regression cases for the three reduced shapes in the issue and check that reapplication stops when a simultaneous rule makes no change. The issue does not identify test file paths, so locate the existing analysis rewrite tests before adding cases; verify the cases terminate and produce the expected parses.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

HermitCrab’s C# analysis parser can hang indefinitely in a simultaneous rewrite when a replacement segment conflicts with an environment segment, consuming one CPU core; the pinned hc.dll reproduced all three reported shapes.

  • Minimal segment case: one-feature t → d / _ a, underlying ta, parse da.
  • Alpha-input case: input [nasal:+, α(place)], output m, environment _ p with p nasal−; parse prefixed mp.
  • Underlying realization case: one rule ʔ → - / _ V[+vocalic], underlying ʔa, parse -a.
  • Suspected source: AnalysisRewriteRule.Apply selects an unbounded SelfOpaquing loop when RHS and environment feature structures are incompatible; SimultaneousPhonologicalPatternRule.Apply returns a word even when it finds no matches.
  • Not known: whether synthesis has the same reapplication behavior.

Next: add regression cases for these reduced shapes and make self-opaquing reapplication stop when the simultaneous rule makes no change.

Reproduction and evidence

Replayed with the Release HermitCrab CLI from Machine commit 4d9b454d42a0da35e058641a65596339a79d115b using dotnet hc.dll -i <grammar.xml> -s <script>. The three original inputs each timed out at 45 seconds; all reduced shapes timed out at 10 seconds. Each timeout used a captured process PID and direct SIGTERM. Reduced runs sampled 107–112% CPU on one process. Compatible-output, no-environment, and feature-removal controls completed promptly.

At the pin, AnalysisRewriteRule.cs:47-69 selects SelfOpaquing after the RHS/environment FeatureStruct.IsUnifiable check fails; :166-173 has no progress or termination guard. SimultaneousPhonologicalPatternRule.cs:22-35 always returns the input word, including when Matcher.AllMatches produces no applicable match. The reduced alpha-input case also hangs after α is removed while retaining the feature-bearing input class, and the glottal case hangs with a single rule, so neither α nor the original rule chain is necessary to the loop.

The pin-matched driver was absent from the exact-pin worktree, so the Tool Release project was built from an exact-pin source archive (SHA-256 of resulting hc.dll: 9cd575be98ddb4e9e32e63114ee699c94d7a395af2074ad15f1557a272404964). The related loop files are unchanged in locally fetched Machine origin/master 9f284a3cc4d5e2c5896f885ba1103fb30594b1e8.

Found while comparing HC-Rust (PanGloss) with pinned hc.dll; PanGloss answers all three in about 1 ms.

Lingua principale
C#
Stelle
29
Fork
16
Merge medio
5g 11h
PR unite (30g)
15

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  4. Apri una pull request che faccia riferimento al numero della issue.

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