internal/fs: fails to build on Plan 9

[dmitshur]

Hello,

I happened to notice that the github.com/evanw/esbuild/internal/fs package has a compilation error when targeting the Plan 9 operating system, which has three Go ports:

$ go tool dist list | grep plan9        
plan9/386
plan9/amd64
plan9/arm

The build error can be reproduced on another platform via cross-compilation, for example:

$ GOOS=plan9 GOARCH=amd64 go build ./...
# github.com/evanw/esbuild/internal/fs
internal/fs/fs_real.go:384:35: undefined: syscall.Errno
$ echo $?
1

syscall documentation says:

On most systems, that error has type syscall.Errno.

But isn't the case on Plan 9.

I don't use Plan 9 myself, but I noticed this when checking that another project at minimum compiles on all Go ports, and that project has esbuild as a dependency. That project doesn't necessarily need to work on Plan 9 and can add "!plan9" build constraints to indicate that, so this isn't causing a serious problem for it.

I'm reporting it here in case you find this information useful. Thanks.

[dmitshur]

I can think of at least 3 general approaches that can be used. Perhaps there are even better ones.

If supporting Plan 9 is completely out of scope of esbuild, you can leave the build error in the ./internal/fs package on Plan 9 as is and close this issue as not planned, that is completely reasonable.

Or you can use build constraints to fix at least the build errors and make ./internal/fs compile. Of course, it might not be very useful to fix a build error without testing that it actually works, so it should probably return a "not implemented" error unless you're interested and willing to implement and support a Plan 9-specific implementation. (See a diff illustrating this direction. Happy to send it as a PR if you like.)

Another approach might be to add a !plan9 build constraint to ./cmd/esbuild and all other packages that aren't supported on that OS. That would essentially "hide" the packages when using GOOS=plan9, to clearly indicate they cannot be used on said OS. A downside is that many .go files would need build constraints. (See a diff illustrating this direction.)

[dmitshur]

Thanks!