After I run the wasm-tools compose example, I cannot run wasm-tools component wit on the composed component. I get the following error:

Error: failed to decode WIT document

Caused by:
    0: failed to decode WIT from import `streams`
    1: unexpected unnamed type

The issue seems to be that the composed component has incorrectly encoded instances. You can see this when looking at one of the instances before and after composition happen. Note: the instance in question is not involved in the composition beyond being a shared dependency of the two components being merged into one composed component:

Before composition

(component
 (type (;0;)
    (instance
      (type (;0;) u32)
      (export (;1;) "wall-clock" (type (eq 0)))
      (type (;2;) (record (field "seconds" u64) (field "nanoseconds" u32)))
      (export (;3;) "datetime" (type (eq 2)))
      (type (;4;) (func (param "this" 1) (result 3))) ;; NOTE: the result points to the "datetime" export
      (export (;0;) "now" (func (type 4)))
    )
  )
;; ...

After composition

(component
  (type (;0;)
    (instance
      (type (;0;) u32)
      (export (;1;) "wall-clock" (type (eq 0)))
      (type (;2;) (record (field "seconds" u64) (field "nanoseconds" u32)))
      (export (;3;) "datetime" (type (eq 2)))
      (type (;4;) (func (param "this" 0) (result 2))) ;; NOTE: the result type points directly to the record
      (export (;0;) "now" (func (type 4)))
    )
  )
;; ...

At some point this instance seems to have one of its functions changed so that its result type points directly to a record field (which is illegal) instead of pointing to a type.

@alexcrichton noted the following on Zulip:

I suspect that this may be an issue with both the decoder and encoder perhaps? The constructs used here were added after the initial implementation of wasm-compose so it hasn't been updated to use exports in the same way. The decoder probably needs an update to read the structure of use-the-exported-item and the encoder needs to be updated to use items as they're exported. Shouldn't be too hard ideally as wit-component deals with similar problems as well, but if you'd like I think opening an issue for this would be good