Package directives should allow specifying a world reference for validation.

[peterhuene]

There should be a way for composition authors to specify the world the output component conforms to such that they can ensure the result is of the expected shape.

Some syntax suggestions:

package foo:bar targets wasi:http/proxy;

Where targets ... is optional.

[peterhuene]

The validation of the output should occur after resolution and basically go through the imports and exports to validate each one is present in the targeted world.

[fibonacci1729]

Presumably we could use wit_component::targets to do this check too but the error returned describing what causes the targets failure is not incredibly informative.

[peterhuene]

That's definitely one option, but it's implementation is pretty heavy compared to reusing all of the type information a resolve document already contains (the implementation of wit_component::targets encodes a new component and then tries to parse it for a validation error).

It should be pretty straight forward to go through each import, error on an import that's not in the target or a matching one that is mismatched on type, and inverse on the exports (error on a missing export or mismatched types for matching export names; i.e. allow more exports than the world specifies).

[fibonacci1729]

That makes sense to me!