Fixes #11750.

The issue is caused by a check on setCallInputs:

if len(arg.metadata.Ignore) > 0 && !arg.metadata.isContextual() { // contextual args already have ignore applied

In this context an argument is considered contextual if either the DefaultPath or DefaultAddress is set. If it is then setCallInputs will not go through the ignore process of directories. The problem: arguments that are contextual (they have a default path) but a user specified a value will not be loaded as part of the contextual loading and will also be ignored in this check. This means applyIgnoreOnDir will never run for them.

Looking into the code I found two potential fixes:

1. Remove the isContextual check and apply ignore on all arguments. Great for simplicity, but it means we are going to run the applyIgnoreOnDir functions on truly contextual arguments twice.
2. Mark contextual arguments only when they are 100% coming from the context directory and not from user inputs.

I went with the second option even though it required more code changes. I'm not 100% sure on the performance impact of running applyIgnoreOnDir twice for contextual args, but it felt wasteful.

As for the test: I created a separate test even though we already have a TestIgnore. This was mainly to keep the existing test clean given that it tests a wide range of cases but for function arguments only. Happy to merge them and look into potential improvements for them.

Tested the change with a dev engine and a module with the following code:

// ...
func New(
	// +defaultPath="."
	// +ignore=["**", "!dagger.json"]
	source *dagger.Directory,
) *NewMod {
	return &NewMod{
		Source: source,
	}
}

func (m *NewMod) TestSource(
	ctx context.Context,
) (string, error) {
	return dag.Container().
		From("alpine:latest").
		WithDirectory("/source", m.Source).
		WithExec([]string{"ls", "-lh", "/source"}).
		Stdout(ctx)
}

Specifying the arg using a dev engine vs v0.19.11:

Not specifying the arg (using the context):

AI disclosure

We don't really do or require this in the project, but given the buzz in social media I thought it would be worth disclosing the use of AI for this PR.

I used it as a guide to look into the code and it helped me understand how arguments are considered contextual, at which point they are loaded and ignored and what is the difference between constructor and function args. Once we found the bug, the code changes were also AI assisted but not vibe coded.