Using // +build directives does not show unknown syscall.Stat_t build error

[henesy]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go1.10 plan9/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

GOARCH='amd64'
GOBIN='/usr/henesy/go/bin'
GOCACHE='/usr/henesy/lib/cache/go-build'
GOEXE=''
GOHOSTARCH='amd64'
GOHOSTOS='plan9'
GOOS='plan9'
GOPATH='/usr/henesy/git'
GORACE=''
GOROOT='/sys/go/go'
GOTMPDIR=''
GOTOOLDIR='/sys/go/go/pkg/tool/plan9_amd64'
GCCGO='gccgo'
CC='6c'
CXX='g++'
CGO_ENABLED='0'
CGO_CFLAGS='-g -O2'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-g -O2'
CGO_FFLAGS='-g -O2'
CGO_LDFLAGS='-g -O2'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build797076891=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I ran/built https://github.com/src-d/go-git with a patch on the https://github.com/src-d/go-billy dependency as per src-d/go-billy#52.

If you go install go-git without any changes, the library builds and you can then build the demo programs in go-git/_examples clone.go and commit.go successfully. Clone will run successfully, but if you build and run commit you get the following crash error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal sys: trap: fault read code=0x0 addr=0x0 pc=0x509499]

goroutine 1 [running]:
gopkg.in/src-d/go-git%2ev4.(*Worktree).doUpdateFileToIndex(0x4209a3aa0, 0x420954200, 0x5c3607, 0x9, 0x3f34afae9c41494b, 0xbc744bc185055bf0, 0x6121711061217110, 0x0, 0x20f94d)
	/usr/henesy/git/src/gopkg.in/src-d/go-git.v4/worktree_status.go:375 +0x149
gopkg.in/src-d/go-git%2ev4.(*Worktree).addOrUpdateFileToIndex(0x4209a3aa0, 0x5c3607, 0x9, 0x3f34afae9c41494b, 0xbc744bc185055bf0, 0x61217110, 0x0, 0x0)
	/usr/henesy/git/src/gopkg.in/src-d/go-git.v4/worktree_status.go:343 +0x15e
gopkg.in/src-d/go-git%2ev4.(*Worktree).Add(0x4209a3aa0, 0x5c3607, 0x9, 0x0, 0x0, 0x0, 0x10, 0x4209a8490)
	/usr/henesy/git/src/gopkg.in/src-d/go-git.v4/worktree_status.go:265 +0x2d1
main.main()
	/usr/henesy/prg/go/git/commit.go:35 +0x12c

If you copy the linux worktree file as follows in go-git and change the header to // +build plan9, the compiler catches the error:
cp worktree_linux.go worktree_plan9.go

sav-cpu% go install
# gopkg.in/src-d/go-git.v4
./worktree_plan9.go:14:22: undefined: syscall.Stat_t

What did you expect to see?

A compiler error pointing out that syscall.Stat_t is not present on Plan 9.

What did you see instead?

No errors at build time. Running the program results in a crash with an error.

[bradfitz]

Sorry, this looks like a bug in go-git (or simply lack of plan9 support in go-git). But there's nothing owned by the Go project here, so closing this bug.

I suggest you file this bug at .... oh, you already did: src-d/go-git#756

That's the right place.

[henesy]

Is the issue not with the //+build not finding the syscall.Stat_t? The lack of support in go-git is not the issue I'm pointing out here. Should //+build if not given a target for a platform (in this case plan9) build the usage of syscall.Stat_t in without throwing an error?

[bradfitz]

Should //+build if not given a target for a platform (in this case plan9) build the usage of syscall.Stat_t in without throwing an error?

I don't know what this question means. But I imagine if you read https://golang.org/pkg/go/build/#hdr-Build_Constraints you'll see how it works.

For questions about Go, see https://golang.org/wiki/Questions.

[henesy]

My apologies for the lack of clarity. I have made a simpler proof of concept: https://github.com/henesy/buildpoc

In the state that the linked demo is in, if built, it yields:

henesy@FatboySlim:~/go/src/github.com/henesy/buildpoc/x/mypkg$ GOOS=plan9 GOARCH=amd64 go install
# github.com/henesy/buildpoc/x/mypkg
./test_plan9.go:12: undefined: syscall.Stat_t

If we delete test_plan9.go (leaving the only built file as test_linux.go) then the build completes as follows:

henesy@FatboySlim:~/go/src/github.com/henesy/buildpoc/x/mypkg$ rm test_plan9.go
henesy@FatboySlim:~/go/src/github.com/henesy/buildpoc/x/mypkg$ GOOS=plan9 GOARCH=amd64 go install
henesy@FatboySlim:~/go/src/github.com/henesy/buildpoc/x/mypkg$ ls
lib.go  test_linux.go  test_plan9_correct.go

If we then go up to the base folder we get a successful build, but running will fail:

sav-cpu% lc
README.md	test.go		x/
sav-cpu% go build
sav-cpu% ./buildpoc
test follows
panic: runtime error: invalid memory address or nil pointer dereference
[signal sys: trap: fault read code=0x0 addr=0x0 pc=0x283abb]

goroutine 1 [running]:
main.main()
	/usr/henesy/go/src/github.com/henesy/buildpoc/test.go:12 +0xcb

[bradfitz]

leaving the only built file as test_linux.go

That's not true and that's why you're confused.

Look at GOOS=plan9 GOARCH=amd64 go list -json github.com/henesy/buildpoc/x/mypkg before & after deleting that file.

And read the URL I sent you before. (https://golang.org/pkg/go/build/#hdr-Build_Constraints)

For questions about Go, see https://golang.org/wiki/Questions.

[henesy]

The list output clarified the situation for me, I had not read the build doc closely enough, thank you. My apologies for the noise.