Add input for alternate dev shells

[zgagnon]

• Add new devShell input
• defaults to default
• add test to make sure we can enter

Passing the devshell in the args line wasn't working, because default was added to the args list in the script. This change give a clean mechanism to enable that

[nicknovitski]

Thank you for the contribution but I don't understand the defect you're encountering. I test setting the arguments input to devShell outputs besides default on this line:

nix-develop/.github/workflows/ci.yml

Line 34 in 8204800

arguments: github:DeterminateSystems/zero-to-nix#${{ matrix.shell }}

You can see from any run of that workflow that the matrix is a list of many different devShells, like example, cpp, hook, etc.

Also, I pushed a branch that adds the same test you've added here, and it passes without your change: https://github.com/nicknovitski/nix-develop/actions/runs/12385445478/job/34571695093

default was added to the args list in the script
When this happens, what are the effects, and what environment is it happening in? Does the action fail, or are the wrong tools present?

In bash, the parameter expansion ${varname:-word} evaluates to word if $varname is unset or null, and to $varname otherwise, so the expression ${@:-./#default} evaluates to ./#default if the parameters variable $@ is null and to $@ otherwise. This is what I see on my system:

~/Source/nix-develop/ > nix develop
bash-5.2$ defaultOr() {
> echo "${@:-./#default}"
> }
bash-5.2$ defaultOr
./#default
bash-5.2$ defaultOr ./#notDefault
./#notDefault

[zgagnon]

So, we have a dev shell for local dev with a lot of tools for doing dev, and a ci one with only the build tools. When passing .#ci as an argument, the default profile was still activating

[nicknovitski]

Then what am I doing wrong here?

nix-develop/.github/workflows/ci.yml

Lines 37 to 46 in c0ddc12

	- name: Test with another local shell target
	uses: ./
	with:
	arguments: ./#notDefault
	- run: which shfmt
	id: should-fail
	continue-on-error: true
	- name: Fail if the action succeeded when the nix command failed
	if: steps.should-fail.outcome == 'success'
	run: exit 1

The notDefault devShell is evaluated, and then which shfmt fails, because it doesn't include that package. The default devShell does, but it's not evaluated, and it's packages are not added to PATH. Here's the ci job where it passes. https://github.com/nicknovitski/nix-develop/actions/runs/12385985222/job/34573126333

[zgagnon]

No, I mean, I am probably doing something wrong. Let me go back and look at it again, and see if I can figure out why it wasn't working for me. At worst, I'll have some logs to share