Changelog

Changelog Style Guide

This guide describes the style for writing RELEASE.md files for hegel-rust. The style is modeled on the Hypothesis changelog.

Which RELEASE.md to write

There are two changelogs, one per published crate:

• RELEASE.md (in the repo root) feeds the top-level CHANGELOG.md and documents changes to the hegel-rust crate (hegeltest).
• hegel-c/RELEASE.md feeds hegel-c/CHANGELOG.md and documents changes to the libhegel C ABI (hegeltest-c).

Write the file for each crate your change affects; a PR affecting both writes both, in the same format. The two crates carry independent version numbers: a change can be breaking for one without being breaking for the other (a breaking C ABI change is a minor bump for hegel-c but, for hegel-rust, only a patch to re-pin and republish against the new engine). Each RELEASE.md picks its own RELEASE_TYPE for its own crate's version. Each release is tagged separately, v<version> for hegel-rust and libhegel-v<version> for hegel-c; only the hegel-c tag gets a GitHub release (titled libhegel v<version>, carrying the binaries), so its RELEASE.md body is also that release's notes.

Because the root crate pins hegeltest-c exactly, every hegel-c release drags hegel-rust along with at least a patch bump to re-pin and republish. That re-pin is just a dependency bump — not a user-facing hegel-rust change — so it does not need a root RELEASE.md: when a PR ships a hegel-c/RELEASE.md and no root one, the release process auto-generates the root entry "This release updates the hegeltest-c dependency to (the new hegel-c version)."

Whether to rely on that autogenerated entry or write a real root RELEASE.md is a judgment call — it cannot be checked automatically; you (or the user) have to decide by looking at what the change actually does. If the PR makes any user-facing change to hegel-rust, write a real root RELEASE.md describing it rather than leaning on the autogenerated dependency-bump line. If hegel-rust only re-pins the new engine, leave the root file out and let the entry autogenerate.

The CI check (release.py check) is only a backstop for the mechanical cases, not the arbiter of that judgment: it requires a hegel-c/RELEASE.md when hegel-c/src/ changes, and a root RELEASE.md when src//hegel-macros/ change without an accompanying hegel-c release (where there would be no entry to autogenerate from). When hegel-c is releasing, it leaves the autogenerate-or-not choice to you.

Choosing RELEASE_TYPE

hegel-rust is currently zerover (0.x.y), so the usual semver mapping does not apply. While we are pre-1.0:

• patch — Bug fixes, internal changes, and new features / non-breaking API additions. The default choice.
• minor — Breaking changes only. Any change that requires users to update their code (renamed/removed APIs, changed signatures, behavior changes that could break downstream tests) is a minor bump.
• major — Not used while we are zerover. Reserve for the eventual 1.0 and beyond.

If you find yourself reaching for minor because the change feels "big," check whether it actually breaks any caller. A large new feature that adds API surface without removing or changing existing behavior is still a patch.

Opening sentence pattern

Every entry should open with a sentence that signals the scope and nature of the change:

• Patch (fixes, improvements, new features): Start with "This patch ..."
• Minor (breaking changes): Start with "This release ..." and explain migration
• Tiny internal-only changes: A bare sentence is fine — "Internal refactoring." or "Clean up some internal code."

The opening verb should tell the reader what kind of change this is:

Describe the user impact, not the implementation

Bad: "Refactored the shrinker's pass scheduling to skip dormant passes."

Good: "This patch improves the performance of shrinking, particularly for tests that are slow to run. Shrinking now spends less time re-running simplification passes that have stopped making progress."

For bug fixes, describe the bug (what went wrong from the user's perspective), not just "fixed a bug":

Bad: "Fix bug in failure database replay."

Good: "Fix failure database replay. Failures saved in the database are now correctly replayed at the start of the next run, instead of being silently skipped."

Length calibration

• Internal-only changes: 1 sentence. ("Refactor some internals.")
• Simple bug fixes: 1-3 sentences. Describe the bug and what changed.
• New features: 1-2 short paragraphs. Describe what it does and why it's useful.
• Breaking changes / API changes: Multiple paragraphs. Include before/after code examples and migration guidance.

Don't pad entries. If a change can be described in one sentence, use one sentence.

Code examples

Include fenced code blocks for:

• New API features (show usage)
• Breaking changes (show before/after)
• Anything where seeing the code is clearer than describing it

Don't include code blocks for bug fixes or internal changes.

References

• Reference GitHub issues when relevant: ([#123](https://github.com/hegeldev/hegel-rust/issues/123))
• Reference previous versions when building on prior work
• Reference related libraries/specs when relevant

Tone

• Third person, present tense for describing behavior
• Professional but conversational — be direct, not formal
• Honest about uncertainty: "This should improve performance", "We expect this to...", "In some cases this may..."
• It's okay to briefly explain why a change was made if the motivation isn't obvious

Things to avoid

• No emojis
• No bullet lists for single-topic entries (use them for multi-topic entries like API cleanups)
• No commit hashes or PR numbers in the text (issue numbers are fine)
• Don't describe the implementation when you can describe the effect
• Don't use vague language like "various improvements" — be specific about what changed
• Don't add marketing language or hype

Examples

Good patch (bug fix):

RELEASE_TYPE: patch

This patch fixes `generators::hashsets` generating duplicate elements in rare cases when the element generator had a very small output space.

Good patch (internal):

RELEASE_TYPE: patch

Internal refactoring of the failure database code.

Good patch (new feature):

RELEASE_TYPE: patch

This patch adds support for `HealthCheck`. A health check is a proactive error raised by Hegel when we detect your test is likely to have degraded testing power or performance. For example, `FilterTooMuch` is raised when too many test cases are filtered out by the rejection sampling of `.filter()` or `assume()`.

Health checks can be suppressed with the new `suppress_health_check` setting.

Good minor (breaking change):

RELEASE_TYPE: minor

This release changes `self` in `#[invariant]` from an immutable reference to a mutable reference:

\```rust
# before
fn my_invariant(&self, ...) {}

# after
fn my_invariant(&mut self, ...) {}
\```

This will require updating your invariant signatures, but should be strictly more expressive.