Hmm, wondering a bit on tag. Overriding an existing image tag is also a valid behavior, should we allow it to have 2 image arguments?

IMO, we should avoid hardcoding the commands in this function and make the caller responsible for picking the desired behavior.
We could add an argument to ImageNames which would take a maximum number of completable images. IMO this could even be an enum with values of One | Two | Infinity.

This would also work nicely with the "two image" case for tag.

Ah, yes, was considering the same. I think just passing an integer would work? (i.e., no magic const needed for this); after all, that's also what we do for number of arguments required (or min/maximum number for those, but minimum number doesn't really apply here);

There are still commands like save or inspect, which can operate on multiple images, so my intent was to avoid having a "magic value" like -1 for that purpose

Ah, right, yeah, not massively disturbed by that though, as it would match, e.g. strings.Replace() and many other stdlib functions, which also use -1 (in this case 0 would even work). Alternative would be to have a separate function for "single" versus "multiple' images. (ImageName(), ImageNames with the latter one taking a limit as second argument.

Alternative would be to have a separate function for "single" versus "multiple' images. (ImageName(), ImageNames with the latter one taking a limit as second argument.

It doesn't solve this issue though, because you still have to distinguish "infinity" from a fixed amount 😅

But yeah, maybe -1 isn't that bad, considering that this pattern is also used in stdlib..

having a new parameter(say count) for ImageNames and -1 for infinity seems to cover all our requirements.
but then the validArgsFunction field only accepts the function of structure
func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective)
as a value. so we won't be able to pass in a new parameter to specify how many suggestions to stop on.

we could have different functions for 1, 2 and infinity tho

(sorry for brevity; commenting from my phone)

ImageNames returns a closure, so it can capture variables passed into it. For example, this would capture the "limit" variable in the function that it returns, so now the function will only allow up to "limit" completions;

func ImageNames(dockerCLI APIClientProvider, limit int) ValidArgsFn {
	return func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
		if limit > 0 && len(args) >= limit {
				return nil, cobra.ShellCompDirectiveNoFileComp
		}
// ...

Basically when calling the ImageNames, it returns a custom function with specific options baked into it (in this case the dockerCLI and limit options)

I see it. thanks