use isomorphic-git to fetch origin, branch, etc instead of shell-js

[tripodsan]

Is your feature request related to a problem? Please describe.
GitUtils uses shell-js to execute git commands to retrieve basic information like remote origin and current branch. this has certain drawbacks:

• only operates on cwd. i.e. the function would need to change the cwd and restore it after executing
• it relies on the existence of a git command
• potentially slower than a native implementation
• potential problems, if the git output changes

advantage:

• no package dependency
• git is very stable and robust, potential implementations might fail

Describe the solution you'd like
Use isomorphic-git (or similar). Since we currently only need a read-only operations, this might be overkill, as it comes with many dependencies. however, we use isomorphic-git also in git-server, so it would already be present in the cli.

Alternative

• find different library
• only use in helix-cli, so that helix-shared stays small

git information that is read during up, deploy, etc:

• isDirty (git status --porcelain)
• getBranch (git rev-parse --abbrev-ref HEAD)
• getRepository (git config --get remote.origin.url)
• getCurrentRevision (git rev-parse HEAD)

[trieloff]

I'm +1 for removing shelljs, but not super excited about adding the isomorphic-git dependency to helix-shared as I'm depending on it for helix-logging and have no need for Git operations there.

Maybe we can just add isomorphic-git as a peer dependency, which will be satisfied in helix-cli, but ignored in helix-logging.

[stefan-guggisberg]

i suggest we add said functionality and the isomorphic-git dependency to helix-cli.

[tripodsan]

it seems we don't need the GitUtils anywhere as in helix-cli. maybe we move it back?

also see my interim fix for the cwd problem:
https://github.com/adobe/helix-shared/blob/new-config/src/GitUtils.js

[stefan-guggisberg]

resolved via PR #52