series-agnostic charm URLs

[Gustavo Niemeyer]

On Wed, Jul 23, 2014 at 7:35 AM, roger peppe <rogpeppe at gmail.com> wrote:
> We want to store charm URLs in mongo-db that are agnostic whether
> the series is specified or not. For example, in a bundle, a service
> is free to specify a series in the charm name or not.

That sounds slightly surprising. How do we plan to define what the
bundle actually means?

While having one or two types to represent the concept may be argued
back and forth, there's an underlying concept that is important: one
form is a loose wildcard that has to be resolved depending on context
before being useful, and was originally designed to be used in command
lines and the such, while the other is a more formal specification
(must have a schema, must have series). Accepting the loosely defined
form in a bundle seems surprising, even if it just means not having a
series, given that deploying the bundle would hopefully be somewhat
deterministic in terms of which distributions are being used.

> I'd like to suggest that we remove the Reference type and use the URL
> type throughout, allowing it to have an unspecified series
> where the string form does not specify a series.
>
> This means that the URL type would be an exact reflection of the string
> form of a charm URL.

As noted above, a Reference may not have a schema as well, so this
suggestion seems to imply that "foo" becomes a valid URL. Maybe having
just URL could be made cleaner, though. This should be judged based on
a more detailed proposal.


gustavo @ http://niemeyer.net