Go: make bindings testable in native Go

[jamesstocktonj1]

Description

When attempting to run unit tests I get the following compilation error when wit-bindgen go bindings are imported:

$ go test ./...
# <go-project>/types/wasi_logging_logging
<go-project>/types/wasi_logging_logging/wit_bindings.go:42:6: missing function body
FAIL    <go-project> [build failed]
FAIL

With the bindings file showing the following:

...
//go:wasmimport wasi:logging/logging@0.1.0-draft log
func wasm_import_log(arg0 int32, arg1 uintptr, arg2 uint32, arg3 uintptr, arg4 uint32)
...

wit-bindgen-go got round this issue by including a blank empty.s assembly file within each of the directories which includes a Go file that uses the //go:wasmimport directive. See here for example.

This tricks the Go compile into thinking there is an assembly implementation of the function which has been declared, and so it no longer complains about the missing function body.

Is this something which we could include in these bindings to get around this build error?

[alexcrichton]

cc @dicej and @asteurer

[dicej]

The empty.s approach sounds reasonable to me. The alternative would be to run the tests using e.g. wasmtime as described here, but it sounds easy enough to support both approaches.

[asteurer]

@jamesstocktonj1 I'm working on the componentize-go tool that is intended to make using wit-bindgen-go much easier. I recently added functionality for unit tests (I'll be cutting a release soon) that should get you going. If you would prefer to use wit-bindgen directly, here's how we do it in componentize-go:

GOOS=wasip1 GOARCH=wasm go test -c -ldflags=-checklinkname=0 -o test.wasm /path/to/specific/package

You'll then use wasmtime run test.wasm to run the unit tests.

Also, keep in mind that we don't yet have a system for building tests that make use of the component model (e.g. tests that call a keyvalue host implementation). That's on my todo list, but it might be a minute until I can get to it.

[dicej]

@asteurer any objection to adding the empty.s files to allow unit tests to build and run natively as well as on a Wasm runtime?

[asteurer]

No objections!

[asteurer]

@dicej Unless there's more to discuss, I think we can close this issue

[dicej]

@jamesstocktonj1 can you confirm that #1557 is sufficient to address this issue?

[jamesstocktonj1]

Not quite... #1557 fixes the "missing function body" error found in bytecodealliance/go-pkg but doesn't fix for the generated types. For this we would need to generate an empty.s for every directory in the bindings.

In the above example the error is coming from the wasi_logging_logging/wit_bindings.go file, adding wasi_logging_logging/empty.s manually fixes this.

[asteurer]

I don't have any concerns generating empty.s files to support this. @dicej Any concerns from you? If not, I'll draft a PR.