feature: add pre-commit support

[Thomy90]

Hi guys,

great tool. I have looked around and this tool is exactly what i am looking for.

I would like to use your tool in combination with pre-commit. The cool thing is then to run your tool during git hooks.

I have seen that for example the project golangci-lint also provide this pre-commit integration.
https://github.com/golangci/golangci-lint/blob/master/.pre-commit-hooks.yaml

If you have questions, feel free to ask me.

Kind Regards,
Thomy90

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[willnorris]

seems reasonable to me on the surface.

Some missing context here is that "pre-commit" seems to refer to https://pre-commit.com/ (and https://github.com/pre-commit). So it looks like we would just add this .pre-commit-hooks.yaml file, and then anyone that wanted to use addlicense would add an entry to their .pre-commit-config.yaml file to the effect of:

repos:
- repo: https://github.com/google/addlicense
  rev: v1.1.1
  hooks:
  - id: addlicense
    args: [ "-c", "Company, Inc", "*.go" ]

We don't need a .pre-commit-config.yaml file in addlicense unless we actually wanted to use pre-commit to run hooks ourselves.

Maybe add a comment at the top of the file that indicates that this is for use with pre-commit.com ?

[Thomy90]

thanks a lot for your advice.

Yes, exactly. Your code snippet is the way i meant how addlicense can be used as a pre-commit hook.

Good point with the comment.

How about a extension in the readme with a code snippet to makes it clear how running addlicense with pre-commit?

For example:

Running with pre-commit

This is the official pre-commit hook for addlicense.

Activate by adding it to your .pre-commit-config.yaml:

repos:
- repo: https://github.com/google/addlicense
  rev: ''  # Use the sha / tag you want to point at
  hooks:
  - id: addlicense
    args: [ "-c", "Company, Inc", "*.go" ]

[rickeylev]

@mco-gh @willnorris Would one of you be willing to review/merge this PR? I, too, would like pre-commit to Just Work with addlicense

[C-Loftus]

Would someone be able to merge pre-commit hook support?

It seems like #160 is all ready and valid but just needs someone to merge it.