bazel coverage with $GOOS.go causes the file to be dropped on non-$GOOS environment.

[yasushi-saito]

Imagine a package with two files:

main.go:

package main
import "log"
func main() {log.Printf("Foo=%d\n", Foo)}

linux.go

package main
const Foo = 100

Running "bazel coverage ..." on Linux works, but the same on Darwin fails with

main.go:3: undefined: Foo

The reason seems to be:

• In coverage mode, rules_go generates a new file, "Coverage_linux.go" that contains coverage-specific stuff.

• It then passes Coverage_linux.go to https://golang.org/src/go/build/build.go:1671, which causes the file to be dropped on non-Linux OS.

Looking at the comment in build.go, the file "linux.go" should be accepted on non-linux platforms.

We can easily work around this problem so no hurry to fix it, but I think it's still a bug.

[jayconrod]

Good catch and good analysis. Thanks for reporting. We declare new cover files and apply coverage as a separate action before compilation. We should probably filter first, then apply coverage, then compile in the same action. Cgo needs to be done in there too, before coverage.

A proper fix may end up being a large refactoring, but we need to rewrite a lot of the cgo logic anyway. A simpler, faster fix should be possible, too.

I wonder if this means build tags in covered files get stripped out, too? I think coverage removes comments.