We need ModuleType 'aliases'

[jonludlam]

Where we have

module type X = Y

we are currently expanding X. This leads to a large number of extra module types html pages being generated. Let's not do that and just link to Y instead, as we do for module aliases.

This is a breaking change obviously, so we should do this before releasing.

[Octachron]

Another motivation for such aliases would be that it makes odoc's behavior uniform in presence of abstract module types.
Currently,

module type Abstract
module type T = Abstract

emits an error message

Failed to compile expansion for module type expression identifier((root Test).Abstract, false) OpaqueModule

because trying to expand T can only fail.

[lpw25]

That's interesting, we definitely shouldn't be giving an error there. Is there also an error for:

module type Abstract
module M : Abstract

[Octachron]

The same error is raised in this case too.

[jonludlam]

I think those warnings have now been squashed.