RFE: Add error-handling example for C API’s wasm_instance_new()

[FGasper]

Motivation

When wasm_instance_new() fails, how should I consume traps if it’s non-NULL? Nothing seems to indicate how I can discover how many traps there are.

Proposed solution

Add examples that show how to report all of the available information about the failure when wasm_instance_new() fails.

[FGasper]

UPDATE: Per the Rust code it looks like the variable can only ever expose a single trap … so should it be renamed?

[Hywan]

Hello,

The naming follows the Wasm standard C API. However, you might be interested by #1744 and #1761. I agree that the documentation should contain more information about it.

Do you want to open a PR?

[FGasper]

Hello,

The naming follows the Wasm standard C API. However, you might be interested by #1744 and #1761. I agree that the documentation should contain more information about it.

Do you want to open a PR?

I’ll comment on the naming in the C API repo, as that seems to be the source of the “naming bug”.

I can look at creating a PR to provide error handling in the C API examples, sure.

Thank you!

[FGasper]

The naming follows the Wasm standard C API.

I don’t see anything in https://github.com/WebAssembly/wasm-c-api/blob/master/include/wasm.h that uses the word “traps” … ?

[syrusakbary]

https://github.com/WebAssembly/wasm-c-api/blob/master/include/wasm.h#L376-L387

I may be confused... but there can be only one trap at a time.

UPDATE: Per the Rust code it looks like the variable can only ever expose a single trap … so should it be renamed?

This might be a good idea. What do you think will be good to rename?

[FGasper]

What do you think will be good to rename?

I’m working on a PR just to rename them “trap”.

[FGasper]

@syrusakbary @Hywan One of the challenges I’ve found is determining how best to convert a trap’s contents into a string. Extracting the message is straightforward enough, but it would be great to be able to extract names from the stack trace as well.

Do you have any insight into how to do this?

[Hywan]

See #2444 which has fixed a bug, and more importantly has added more documentation.

[Hywan]

Everything is documented here, https://wasmerio.github.io/wasmer/crates/doc/wasmer_c_api/wasm_c_api/trap/index.html

[FGasper]

Everything is documented here

// Do something with the trap.

^^ @Hywan Are there any examples of this? I don’t see any.

It’s straightforward enough to get the error message itself, but what is to be done with the origin and trace?

[Hywan]

This part is not documented yet. wasm_trap_origin returns a wasm_frame_t, and wasm_trap_trace returns a fills out a wasm_frame_vec_t. Please open an issue for that specifically :-).