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go-conventionalcommits

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Fu powers to parse your commit messages as the Conventional Commits specification demands.

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# go-conventionalcommits

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**A parser for [Conventional Commits v1.0](https://www.conventionalcommits.org/en/v1.0.0/#specification) commit messages**.

> Fu powers to parse your commits!

This repository provides a library to parse your commit messages according to the Conventional Commits v1.0 specification.

## Installation

```console
go get github.com/leodido/go-conventionalcommits
```

## Docs

[![Documentation](https://img.shields.io/badge/godoc-reference-blue.svg?style=for-the-badge)](http://godoc.org/github.com/leodido/go-conventionalcommits)

The [parser/docs](parser/docs/) directory contains `.dot` and `.png` files representing the finite-state machines (FSMs) implementing the parser.

## Usage

### Parse

Your code base uses only single line commit messages like this one?

```console
feat: awesomeness
```

No problem at all since the body and the footer parts are not mandatory:

```go
m, _ := parser.NewMachine().Parse([]byte(`feat: awesomeness`))
```

### Full conventional commit messages

Imagine you have a commit message like this:

```console
docs: correct minor typos

see the issue for details

on docs edits.

Reviewed-by: Z
Refs #133
```

Go with this:

```go
opts := []conventionalcommits.MachineOption{
    WithTypes(conventionalcommits.TypesConventional),
}
res, err := parser.NewMachine(opts...).Parse(i)
```

Or, more simpler:

```go
res, err := parser.NewMachine(WithTypes(conventionalcommits.TypesConventional)).Parse(i)
```

### Types

This library provides support for different types sets:

- **minimal**: fix, feat
- **conventional**: build, ci, chore, docs, feat, fix, perf, refactor, revert, style, test
- **falco**: build, ci, chore, docs, feat, fix, perf, new, revert, update, test, rule

At the moment, those types are at build time. Which means users can't configure them at runtime.

Anyway, there's also a **free-form** types set that accepts any combination of printable characters (before the separator after which the commit description starts) as a valid type.

You can choose the type set passing the `WithTypes(conventionalcommits.TypesConventional)` option as shown above.

### Options

A parser behaviour is configurable by using options.

You can set them calling a function on the parser machine.

```go
p := parser.NewMachine()
p.WithBestEffort()
res, err := p.Parse(i)
```

Or you can provide options to `NewMachine(...)` directly.

```go
p := parser.NewMachine(WithBestEffort())
res, err := p.Parse(i)
```

### Strict UTF-8 input

By default, the parser remains byte-permissive: grammar acceptance does not
guarantee that every byte in a commit message is well-formed UTF-8.

Enable strict validation on the parser-specific machine when the entire
original input must be valid UTF-8:

```go
machine := parser.NewMachine()
machine.WithStrictUTF8()
res, err := machine.Parse(input)
```

Strict UTF-8 validation runs before grammar parsing. The first malformed byte
returns a nil message and an error such as `invalid UTF-8: col=12`, where the
column is the zero-based byte offset in the original input. This input
precondition also takes precedence over best-effort parsing, so malformed UTF-8
never produces a partial message.

Malformed input matches the `parser.ErrInvalidUTF8` sentinel. Use
`errors.As` with `*parser.InvalidUTF8Error` to retrieve its exact zero-based
`ByteOffset` without parsing the error string:

```go
if errors.Is(err, parser.ErrInvalidUTF8) {
    var invalid *parser.InvalidUTF8Error
    if errors.As(err, &invalid) {
        fmt.Println(invalid.ByteOffset)
    }
}
```

`WithStrictUTF8` belongs to `parser.Machine`, the interface returned by
`parser.NewMachine`. Other `conventionalcommits.Machine` implementations cannot
receive this parser-specific setting accidentally.

### Best effort

The best effort mode will make the parser return what it found until the point it errored out,
if it found (at least) a valid type and a valid description.

Let's make an example.

Suppose this input commit message:

```console
fix: description
a blank line is mandatory to start the body part of the commit message!
```

The input does not respect the Conventional Commits v1 specification because it lacks a blank line after the description (before the body).

Anyways, if the parser you're using has the best effort mode enabled, you can still obtain some structured data since at least a valid type and description have been found!

```go
res, err := parser.NewMachine(WithBestEffort()).Parse(i)
```

The result will contain a `ConventionalCommit` struct instance with the `Type` and the `Description` fields populated and ignore the rest after the error column.

The parser will still return the error (with the position information), so that you can eventually use it.

## Trailer parsing

The parser implements [Conventional Commits v1.0 clauses 8 to 10](https://www.conventionalcommits.org/en/v1.0.0/#specification) for trailers (also called footers). A few behaviors are worth calling out.

### Trailer-shaped lines in the body stay in the body

A line in the body that looks like a trailer (say, `Fixes #123`) is not picked up as one. The trailer block is only the run of trailer lines at the end of the message, with a blank line between it and the body.

Given this commit message:

```console
fix: x

This paragraph mentions
Fixes #123 in passing.

Reviewed-by: X
```

```go
in := []byte("fix: x\n\nThis paragraph mentions\nFixes #123 in passing.\n\nReviewed-by: X")
m, _ := parser.NewMachine(parser.WithTypes(conventionalcommits.TypesFreeForm)).Parse(in)
// m.Body    == "This paragraph mentions\nFixes #123 in passing."
// m.Footers == map[reviewed-by:[X]]
```

A message whose body ends with a trailer-shaped line but has no real trailer block keeps the line as body content:

```console
fix: x

This paragraph mentions
Fixes #123 in passing.
```

```go
in := []byte("fix: x\n\nThis paragraph mentions\nFixes #123 in passing.")
m, _ := parser.NewMachine(parser.WithTypes(conventionalcommits.TypesFreeForm)).Parse(in)
// m.Body    == "This paragraph mentions\nFixes #123 in passing."
// m.Footers == map[]
```

### Multi-line trailer values

Clause 10 says a trailer's value can contain spaces and newlines. The value keeps going until the parser sees the next trailer (a `Token: value` line) or a blank line.

Given this commit message:

```console
fix: x

BREAKING CHANGE: this is a long
  explanation that wraps
  across several lines
Reviewed-by: X
```

```go
in := []byte("fix: x\n\nBREAKING CHANGE: this is a long\n  explanation that wraps\n  across several lines\nReviewed-by: X")
m, _ := parser.NewMachine(parser.WithTypes(conventionalcommits.TypesFreeForm)).Parse(in)
// m.Footers == map[
//   breaking-change: ["this is a long\n  explanation that wraps\n  across several lines"]
//   reviewed-by:     ["X"]
// ]
```

### Blank-separated trailers

Clause 8 lets you put a blank line between trailers. Both layouts parse the same way.

Blank-separated:

```console
feat: x

Fixes #1

Reviewed-by: X
```

Adjacent:

```console
feat: x

Fixes #1
Reviewed-by: X
```

```go
parser.NewMachine(...).Parse([]byte("feat: x\n\nFixes #1\n\nReviewed-by: X"))
parser.NewMachine(...).Parse([]byte("feat: x\n\nFixes #1\nReviewed-by: X"))
// Both yield: footers == map[fixes:[1] reviewed-by:[X]]
```

### What `Parse` returns

In strict mode (best-effort off), `Parse` returns one of:

- `(*ConventionalCommit, nil)` on success
- `(nil, error)` on failure

It never returns `(nil, nil)`, so a `nil` first value always means the second value is the real error.

In best-effort mode you can also get `(*ConventionalCommit, error)`: a partial commit recovered before the parser ran into the problem, plus the error telling you where it stopped.

## Performances

To run the benchmark suite execute the following command.

```console
make bench
```

All the parsers have the best effort mode on.

On my machine<sup>[1](#mymachine)</sup>, these are the results for the `slim` parser with the default - ie., `minimal`, commit message types.

```console
[ok]_minimal______________________________________-12          4876018       242 ns/op     147 B/op       5 allocs/op
[ok]_minimal_with_scope___________________________-12          4258562       284 ns/op     163 B/op       6 allocs/op
[ok]_minimal_breaking_with_scope__________________-12          4176747       288 ns/op     163 B/op       6 allocs/op
[ok]_full_with_50_characters_long_description_____-12          1661618       700 ns/op     288 B/op      10 allocs/op
[no]_empty________________________________________-12          4059327       292 ns/op     112 B/op       3 allocs/op
[no]_type_but_missing_colon_______________________-12          2701904       444 ns/op     200 B/op       6 allocs/op
[no]_type_but_missing_description_________________-12          2207985       539 ns/op     288 B/op       8 allocs/op
[no]_type_and_scope_but_missing_description_______-12          1969390       605 ns/op     312 B/op      10 allocs/op
[no]_breaking_with_type_and_scope_but_missing_desc-12          1978302       606 ns/op     312 B/op      10 allocs/op
[~~]_newline_in_description_______________________-12          2115649       563 ns/op     232 B/op      11 allocs/op
[no]_missing_whitespace_in_description____________-12          1997863       595 ns/op     312 B/op      10 allocs/op
```

Using another set of commit message types, for example the `conventional` one, does not have any noticeable impact on performances, as you can see below.

```console
[ok]_minimal______________________________________-12          5297486       228 ns/op     147 B/op       5 allocs/op
[ok]_minimal_with_scope___________________________-12          4498694       267 ns/op     163 B/op       6 allocs/op
[ok]_minimal_breaking_with_scope__________________-12          4431040       273 ns/op     163 B/op       6 allocs/op
[ok]_full_with_50_characters_long_description_____-12          1750111       692 ns/op     288 B/op      10 allocs/op
[no]_empty________________________________________-12          3996532       294 ns/op     112 B/op       3 allocs/op
[no]_type_but_missing_colon_______________________-12          2657913       451 ns/op     200 B/op       6 allocs/op
[no]_type_but_missing_description_________________-12          2172524       553 ns/op     288 B/op       8 allocs/op
[no]_type_and_scope_but_missing_description_______-12          1880526       637 ns/op     312 B/op      10 allocs/op
[no]_breaking_with_type_and_scope_but_missing_desc-12          1879779       635 ns/op     312 B/op      10 allocs/op
[~~]_newline_in_description_______________________-12          2023514       592 ns/op     232 B/op      11 allocs/op
[no]_missing_whitespace_in_description____________-12          1883124       623 ns/op     312 B/op      10 allocs/op
```

As you may notice, this library is very fast at what it does.

Parsing a commit goes from taking about the same amount of time (~299ns) the half-life of polonium-212 takes<sup>[2](#nanosecondwiki)</sup> to less than a microsecond.

## Build

To build this Go library locally just run:

```bash
make
```

You'd need Ragel 6.10 to be present into your machine.

---

- <a name="mymachine">[1]</a>: Intel Core i7-8850H CPU @ 2.60GHz
- <a name="nanosecondwiki">[2]</a>: <https://en.wikipedia.org/wiki/nanosecond>

---

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