go/packages: ignore cgo errors

[bwmarrin]

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

$ go version
go version go1.12.7 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/bwmarrin/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/bwmarrin/.go"
GOPROXY=""
GORACE=""
GOROOT="/home/bwmarrin/.go/root"
GOTMPDIR=""
GOTOOLDIR="/home/bwmarrin/.go/root/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build824270571=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Opened a new temp package in my GOPATH src folder. Tested auto completion and it worked fine. Then I added an import for the http package. Then I tested and auto completion no longer worked for items within my temp package.

After hunting down some other issues, I found the below command.

go list -e -json -compiled

Running that without the http package returned details without an error. Running it with the http package returned an error, along with the details I expected.

exec: "gcc": executable file not found in $PATH

Which, I assume is to say gcc is required for this to work right. So I installed gcc, and now everything works as expected.

I'm not sure if this is a bug, or working as intended. It took me several hours to figure out why my auto completion wasn't working and thought I'd share it here in case it wasn't intended behaviour and so maybe others might be helped, possibly.

What did you expect to see?

I expected go auto completion to "just work" even after adding the http package without needing to install a compiler I didn't think I needed.

What did you see instead?

Auto completion failed to work for things within the test package after adding http import.

[stamblerre]

To confirm, this was when you were importing the net/http package in the standard library?

[bwmarrin]

Correct.

[stamblerre]

/cc @jayconrod for more clarity on why go list would behave this way. This sound similar to a few other issues users have encountered with gopls, specifically #33107 (comment) and #33018 (comment).

@bwmarrin: And this code compiles without any problems?

[jayconrod]

net/http depends on packages that have cgo code. It looks like these are runtime/cgo, net, and crypto/x509.

If the -compiled flag is passed to go list, listed packages and their dependencies are compiled, and the paths to the compiled .a files are included in the output. If cgo is enabled, a C compiler is required to build those packages. I'm guessing gopls uses the compiled .a files for type information, but even if it didn't, cgo may be required for type checking.

@bwmarrin Have you tried disabling cgo by setting CGO_ENABLED=0 in your environment? I don't believe cgo is disabled automatically depending on whether there is a C compiler in PATH.

[bwmarrin]

@stamblerre - yes, the test code compiled fine. I could create a repo with an example, if that helped.

@jayconrod - No, I didn't try disabling cgo. Once I found the error I just went ahead and installed gcc. I just hadn't needed it on this dev machine yet so never installed it but it wasn't a big deal to add it if that's what it took to get things working so I could get back to work ;)

[stamblerre]

I don't believe cgo is disabled automatically depending on whether there is a C compiler in PATH.

@jayconrod: Is this something we could possibly do in the go command, or would go/packages have to handle this error?

[gopherbot]

Change https://golang.org/cl/190177 mentions this issue: go/packages: add test case for golang/go#33462

[stamblerre]

I think this is fairly fixable in go/packages. Sent @matloob a test case so that this issue can be resolved there.