# Validating commit messages with dart and Lefthook


Something I had been trying to work out for my Flutter project for some time was validating commit messages, initially, I used `commit-msg-validate` but having a node dependency in a Flutter/Dart project does not seem right and when the team grew to beyond myself I worked on moving all of the automation scripts I had written in JS over to dart and while there are still a few node dependencies left, they are purely for use in the CI pipeline.

For the purpose of executing git-hooks across the team, I added [Lefthook](https://github.com/Arkweid/lefthook) to the project and initially only used `pre-push` for executing the test scripts, but only recently had an idea for how to execute the `commit-msg` hook.

## The Hook

I found out that the commit message is stored in a plain text file `COMMIT_EDITMSG` inside the `./git` folder, which would be easy to read up into a string within Dart.

I added a `git_hook` folder with a `commit_message.dart` file, which I could later run from Lefthook.

Within our project, and I suspect many at this point follow the semantic commit message approach, you can read more about that [HERE](https://nitayneeman.com/posts/understanding-semantic-commit-messages-using-git-and-angular/).

Our commit message file looks like this:

```
*import *'dart:io';

*dynamic *main() {
  *final *rootDir = Directory.*current*;
  *final *commitFile = File(rootDir.path + "/.git/COMMIT_EDITMSG");
  *final *commitMessage = commitFile.readAsStringSync();

  *final *regExp = RegExp(
    r'(fix|feat|wip|none|chore|refactor|doc|style|test)\(\w+\):\s?(\[\DEV-\d+])?.+',
  );

  *final *valid = regExp.hasMatch(commitMessage);
  *if *(!valid) exitCode = 1;
}
```


## Let's break it down

```
*final *rootDir = Directory.*current*;
*final *commitFile = File(rootDir.path + "/.git/COMMIT_EDITMSG");
*final *commitMessage = commitFile.readAsStringSync();
```


The first few lines are quite simple, here we are getting the current directory and with that creating a File reference to `COMMIT_EDITMSG`, which is then read up to a string, which can be validated with the following Regular Expression.

```
*final *regExp = RegExp(
    r'(fix|feat|wip|none|chore|refactor|doc|style|test)\(\w+\):\s?(\[\DEV-\d+])?.+',
  );
```


This validates our commit message format, which starts with a prefix, these are most important for the automation scripts used to generate our version number as well as the changelog.

### The Expression

```
(fix|feat|wip|none|chore|refactor|doc|style|test)
```


Each message has to begin with one of the above strings, after that we have our scope:

```
\(\w+\)
```


This is normally used as a module or feature reference, just to provide a small context on where the change is happening.

After that we have the optional space and Jira ticket references, all our Jira issues begin with `DEV`.

```
\s?(\[\DEV-\d+])
```


Finally, any characters after that,

```
.+
```


In our case a valid commit message would look like this:

```
feat(video): [DEV-1223] added support for leading text
feat(video): added support for leading text
```


### The Validation

After that, we can validate our commit message against our Regular Expression using:

```
*final *valid = regExp.hasMatch(commitMessage);
*if *(!valid) exitCode = 1;
```


If not valid, we simply set the `exitCode` to 1, anything other than 0 is an error, which would terminate the script and prevent you from commit with an incorrect message.

## Adding in Lefthook

Now that our script is complete, we can update Lefthook so that this script can be executed whenever one of us attempts a git commit.

```
commit-msg:
  commands:
    validate:
      run: flutter pub run ./git_hooks/commit_message.dart
```


After adding the above snippet to `lefthook.yaml`, one simply needs to run `lefthook install` to activate the hook.

```
Lefthook v0.7.2
RUNNING HOOKS GROUP: commit-msg

EXECUTE > validate
The message: none(lefthook): added commit validation

SUMMARY: (done in 1.13 seconds)
✔️  validate
```


If everything has worked, after your next commit, assuming your message met the required format, you should see something similar to the above message.

I hope you found this interesting, and if you have any questions, comments, or improvements, feel free to drop a comment. Enjoy your Flutter development journey :D

If you liked it, a like would be awesome, and if you really liked it, a [cup of coffee](https://www.buymeacoffee.com/remelehane) would be great.

Thanks for reading.

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