`heroku ci:run` needs explanatory warnings if the current git repo is in detached head state

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Do you want to request a feature or report a bug?

Feature, I guess. Though it depends on whether one considers error handling/logging to be a feature or the lack thereof to be a bug.

What is the current behavior?

When running heroku ci:run from a detached head state, the Heroku CLI fails silently, leaving no explanation or warnings about the reasoning behind this behavior.

Suppose we're working on a git repo my-webserver, configured to deploy to the Heroku app my-heroku-webserver.

The following sequence of commands works fine:

cd my-webserver
git checkout dev
heroku ci:run --app my-heroku-webserver

The tests will build and run as configured, yay!

However, if we instead checkout to a specific commit and thus enter a detached head state:

cd my-webserver
git checkout 0a2dac
heroku ci:run --app my-heroku-webserver

Then the Heroku CLI exits silently with an exit code of 1. The error code 1 is not the issue here (see below) -- the issue is that there is no warning/error message or logging explaining the failure.

What is the expected behavior?

To be clear, I am NOT proposing that heroku ci:run should work in a detached head state -- we need to know the branch name, so it stands to reason that we must be on a branch. (For the details of what's exactly going on, we get the branch name here by calling git --symbolic-ref --short HEAD.)

However, it would probably be a good idea to either pass through the stderror from the git call to the user on failure or else to explain why the command is failing.

Until that's set up, I figured it might be good to get an issue up for this -- I ran into this while trying to run the Heroku CLI inside GitHub actions, which by default checks out a SHA, not a branch. Hopefully this can help others who are banging their heads against the same issue until the quick fix for this eventually works its way in.

heroku / cli