Turns out I'm hitting this one because I need the pin/ls command to only rely on the CoreAPI instead of the IpfsNode, which means finishing the internal refactoring there, started by @magik6k if I'm not mistaken.

I'm hesitating between several options:

Ls(context.Context, ...options.PinLsOption) (<-chan Pin, error)

The one you suggested in this PR.
Pro: it's simple
Cons: no way to return errors after the streaming started

Ls(context.Context, ...options.PinLsOption) (<-chan Pin, <-chan error)

Pro: errors while streaming can be returned. A bit clunky to use but less that the third solution
Cons: errors before the streaming need to be sent in the error channel which make it a bit weird to implement

This API can be used like this:

var result []iface.Pin

pins, errC := api.Pin().Ls(ctx)
for pin := range pins {
	result = append(result, pin)
}

if err := <-errC; err != nil {
	return nil, err
}

Third option:

Ls(context.Context, ...options.PinLsOption) (<-chan Pin, <-chan error, error)

Pro: errors while streaming can be returned. Simpler to implement.
Cons: Clunky to use.

Any preference ?

Maybe better:

// Pin holds information about pinned resource
type Pin interface {
	// Path to the pinned object
	Path() path.Resolved

	// Type of the pin
	Type() string

	// if not nil, an error happened.
	Err() error
}

Ls(context.Context, ...options.PinLsOption) (<-chan Pin, error)

I'm going for this solution.