refactor: provide more descriptive panic messages

[rvolosatovs]

Refs #967

From:

'IndexMap: key not found'

To:

interface with index 7 of type with index 54 missing from imported instances

While the message is still pretty cryptic, at least the domain the panic originates from is somewhat clear

Note, that the second panic occurs when constructing metadata of a component importing wasi-http as http (e.g. in https://github.com/bytecodealliance/wit-bindgen test cases)

[alexcrichton]

Thanks! There's quite a lot of panicking statements throughout wit-component though and ergonomically I don't think it's worth going through all of them and improving the messages (not that this does that, of course, more that I don't think it necessarily makes sense to continue this trend). That being said panics are internal errors that users, theoretically, should never encounter. In that sense a user shouldn't ever have to decipher a panic message and instead they'd open an issue where developers would diagnose (perhaps with the more useful messages here).

Given all that I think the best thing to do would either be:

• Fix the underlying bugs and not update the panic messages for now.
• Change the panics here to errors and instead return an error if the conditions are violated.

Does that sound reasonable?

[peterhuene]

If no one has yet looked at fixing #967, I should have some time soon to dive into it after I get a bunch of feature work on cargo component in.

[alexcrichton]

I believe this was addressed in #974 so I'm going to close this. Thanks for the PR though!