Support environment variables in commit parsers

[harlequin]

Is there an existing issue or pull request for this?

• I have searched the existing issues and pull requests

Feature description

I have a monorepo with around 100 projects. At the moment I have to maintain in every single project folder an own cliff.toml, because git-cliff has two missing features, which denies a --config-url usage:-

(1) It would be great if the commit-parser can include somehow a pre-processor for env variables

This is what the project cliff.toml looks like

`{ message = "^feat\\(app1):", group = "<!-- 0 -->🚀 Features" },`

Wish would be

`{ message = "^feat\\(${GIT_CLIFF_SCOPE}):", group = "<!-- 0 -->🚀 Features" },`

With this we would have the possibility to define the scope via GIT_CLIFF_SCOPE

(2) Initial tag can not be set via cli or env variable

At the moment the cliff.toml looks like

```
[git]
tag_pattern = "app1-v[0-9]+\\.[0-9]+\\.[0-9]+" # THIS CAN BE SET SUCCESSFUL VIA CLI
[bump]
initial_tag = "app1-v1.0.0" # <- THIS IS THE REQUEST 
```

It would be great to get also the initial_tag as env variable or cli option in order

Desired solution

As described above

Alternatives considered

None

Additional context

None

[welcome]

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[orhun]

Hello @harlequin 👋🏼 Thanks for reporting.

(1) It would be great if the commit-parser can include somehow a pre-processor for env variables

This makes sense to me and we could probably implement it. Would you be interested in contributing this feature?

Initial tag can not be set via cli or env variable

This is currently possible via CLI: --bump --tag

Also there was #1140 but decided not to implement it because this is already supported. But maybe we could support --initial-tag at this point because --bump --tag is not that intuitive.

cc @Muhammad-Owais-Warsi what do you think?