cmd/wasirun: add --env-inherit flag from wazero

[ydnar]

This enables GOOS=wasip1 GOARCH=wasm go test -exec 'wasirun --env-inherit --dir /' <package>

The go test command sets the working directory AND $PWD to the package source directory when running. This passes PWD through at the time wasirun is executed, rather than the value of PWD at the time go test is executed (typically the module root).

[achille-roussel]

Thanks for the contribution!

[ydnar]

It took a while to track down why go test -exec couldn't find source-relative test data. Turns out os.Getwd needs $PWD set to work on wasip1.

[achille-roussel]

Ah yes, the dependency on PWD is something we should probably have documented properly somewhere when Go 1.21 comes out, thanks for the feedback!

[ydnar]

Wonder if it makes sense to have PWD automatically set, or have a --pwd flag?

I considered augmenting the --dir option to accept a bare environment variable name, which would capture the value from the current wasirun process.

[achille-roussel]

That would probably be a useful addition, I would advise doing this only if the PWD environment variable does not already exists, then we set it to the current working directory.

Which environment were you running in that did not set PWD?

[ydnar]

We had a Make target that set PWD, but since exec.Cmd doesn’t interpolate shell variables, the interpolation happened in Make. The old, wrong version:

wasm-test:
	$(WASM_ENV) gotip test -v -exec "wasirun --non-blocking-stdio --dir / --env PWD=$$PWD" $(TEST_PACKAGES)

With --env-inherit:

wasm-test:
	$(WASM_ENV) gotip test -v -exec "wasirun --non-blocking-stdio --dir / --env-inherit" $(TEST_PACKAGES)

I think allowing --env to pass the current value of the named variable could be useful:

wasm-test:
	$(WASM_ENV) gotip test -v -exec "wasirun --non-blocking-stdio --dir / --env PWD" $(TEST_PACKAGES)