Sample

Distinguish winnow error handling paths where alt combinator discards deep branch errors in favor of the last branch unless cut_err is used, try_map failures yield recoverable Backtrack rather than fatal Cut, and ContextError formatting displays only the innermost label while InputError drops context annotations entirely

sha256:37c7408540f30c3e0ea78c7a69f7ddb967574c1c9fbfebcf11fbf25d3bbe07d5

Case

Goal

Distinguish winnow error handling paths where alt combinator discards deep branch errors in favor of the last branch unless cut_err is used, try_map failures yield recoverable Backtrack rather than fatal Cut, and ContextError formatting displays only the innermost label while InputError drops context annotations entirely HOW

Packages

winnow 1.0.4

Environment

rust

Created

2026-08-16T12:43:07Z

Commonly assumed

When an alt combinator fails on invalid input after partially matching an alternative, ContextError preserves the error details and byte offset from whichever branch parsed deepest.

The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.

Contract

• assert alt with ContextError discards a partial match in an earlier branch and returns the error and offset of the last evaluated branch, while cut_err prevents backtrack and preserves the deep failure site
• assert try_map produces ErrMode::Backtrack rather than Cut on external validation failure so alt continues trying subsequent branches
• assert TreeError preserves all failed branches of an alt in a hierarchical Alt structure rather than overwriting them with the last branch
• assert InputError ignores AddContext labels and records the remaining input slice, whereas ContextError formats the innermost StrContext::Label and all Expected tokens but renders empty if unannotated
• assert Parser::parse erases the ErrMode modal distinction into ParseError and reports the offset of trailing unconsumed input when the inner parser succeeds partially

Files

• Cargo.lock
• Cargo.toml
• NOTES.md
• csx.json
• src/lib.rs

Download the verified artifact (tar.gz) — the exact bytes the contract ran against

Origin Seeder

csx-seed

Verification receipts

• rust 1 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · cargo@1 · 2026-08-16 · ed25519:d91480838ac982c9