changelog

name	changelog
description	Changelog style guide for writing RELEASE.md files. Use when creating or reviewing RELEASE.md, writing changelog entries, or preparing a PR that needs release notes.

Changelog Style Guide

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

Choosing RELEASE_TYPE

hegel-ocaml 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:

Change type	RELEASE_TYPE	Opening pattern
Bug fix	patch	"This patch fixes ..." or "Fix ..."
New feature	patch	"This patch adds ..."
Improvement	patch	"This patch improves ..."
Performance	patch	"This patch improves the performance of ..." or "Optimize ..."
Deprecation	minor	"This release deprecates ..."
Breaking change	minor	"This release changes ..." (then explain migration)
Internal-only	patch	"Internal refactoring." / "Refactor some internals." / "Clean up some internal code."

Describe the user impact, not the implementation

Bad: "Refactored the socket handling code to use a shared connection pool."

Good: "This patch changes the way the client manages the engine to run a single persistent process for the whole test run. This should improve the performance of running many hegel tests."

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

Bad: "Fix bug in engine crash detection."

Good: "Fix engine crash detection. The client now properly detects when the hegel engine process exits unexpectedly, instead of hanging indefinitely."

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: ([#24](https://github.com/hegeldev/hegel-ocaml/issues/24))
• 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 flaky generation failures not being displayed.

Good patch (internal):

RELEASE_TYPE: patch

Internal refactoring of the protocol handling code.

Good patch (new feature):

RELEASE_TYPE: patch

Add support for building and running on the OxCaml compiler (ocaml-variants.5.2.0+ox). 
The ppx_hegel_generator PPX deriver now works on both standard OCaml and OxCaml by 
abstracting over ppxlib AST differences (labeled tuples, constructor modalities) 
via a platform-selected compatibility module.

Good minor (breaking change):

RELEASE_TYPE: minor

This release changes the public API for running Hegel tests to a new `let%hegel_test` PPX extension.
\```ocaml
# before
let my_invariant = Hegel.run_hegel_test (fun tc -> ...)

# after
let%hegel_test my_invariant tc = ...
\```

This will require updating your test declarations, but will enable integration with 
Antithesis and `dune runtest` and automatically register tests with the new test runner.