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What's new in fast-check 4.8.0?

· 3 min read
Nicolas Dubien
Nicolas Dubien
fast-check maintainer

Nesting an arbitrary number of .chain calls has never been simple with fast-check. This release introduces chainUntil, a new combiner dedicated to iterative chaining. It runs as a loop, keeps going until you decide to stop and supports proper shrinking even on very long chains.

Continue reading to explore the detailed updates it brings.

Iterative chaining with chainUntil​

The new chainUntil arbitrary takes a starting arbitrary and a chainer function. It first generates a value from the starting arbitrary, then repeatedly calls chainer with the latest value to produce the next arbitrary in the chain. The loop stops as soon as chainer returns undefined,and the value emitted by chainUntil is the last one produced along the way.

fc.chainUntil(
  // Start from a tuple containing one value in 0..20,
  fc.nat(20).map((n) => [n]),
  // Then, if value is greater than 10, append another value in 0..20
  (tuple) => (tuple.at(-1) > 10 ? fc.nat(20).map((n) => [...tuple, n]) : undefined),
);
// Examples of generated values: [14,6], [2], [1], [20,2], [18,17,13,3]…

While doable with .chain it required nesting calls but the depth of the nesting has to be known upfront. With chainUntil, variable-length dependent generation is possible.

Changelog since 4.7.0​

The version 4.8.0 is based on version 4.7.0.

Features​

  • (PR#6678) Add chainUntil arbitrary for iterative chaining

Fixes​

  • (PR#6965) Bug: Restore ability not to use skipLibCheck
  • (PR#6877) CI: Lowercase discussion_category_name to "announcements"
  • (PR#6878) CI: Scope permissions of clean-caches
  • (PR#6880) CI: Add PR-authoring guidance for Claude
  • (PR#6887) CI: Delete CLAUDE.md
  • (PR#6888) CI: Use tilde ranges for security dependency overrides
  • (PR#6891) CI: Disable Renovate updates on pnpm overrides
  • (PR#6899) CI: Scope Claude hooks to $CLAUDE_PROJECT_DIR
  • (PR#6905) CI: Enable pnpm global virtual store
  • (PR#6933) CI: Pin pnpm in npm install commands
  • (PR#6932) CI: Grant discussions: write to release jobs
  • (PR#6935) CI: Skip PR template check for dubzzz
  • (PR#6937) CI: Mirror the repo to tangled
  • (PR#6938) CI: Add missing runs-on for tangled
  • (PR#6889) Doc: Add release notes for fast-check 4.7.0
  • (PR#6900) Doc: Fix broken API reference links
  • (PR#6844) Doc: Extract manual setup guide into dedicated page
  • (PR#6845) Doc: Add index pages for documentation sections
  • (PR#6918) Doc: Fix Documentation link to point to first doc page
  • (PR#6939) Doc: Link to Tangled mirror of fast-check
  • (PR#6934) Test: Tolerate \p{...} value drift in docs tests
  • (PR#6951) Test: Fix poisoning tests for latest Node