"Can't load package" for `package main` declaration

[kkuchta]

I'm trying to set up a hello world go project using modules and vscode. I'm using the go extension without the language server. I'm getting an error on the line package main when it seems like it should build cleanly.

My project consists of two files:

// src/go.mod
module whatever

go 1.14

// src/modtest.go
package main

import "fmt"

func main() {
	fmt.Println("hello, world")
}

VS Code shows an error on package main:

/Users/kevin/code/go/modtest>Finished running tool: /usr/local/bin/go build _/Users/kevin/code/go/modtest/src
can't load package: package _/Users/kevin/code/go/modtest/src: cannot find package "_/Users/kevin/code/go/modtest/src" in any of:
	/usr/local/Cellar/go/1.14.3/libexec/src/_/Users/kevin/code/go/modtest/src (from $GOROOT)
	/Users/kevin/code/go/src/_/Users/kevin/code/go/modtest/src (from $GOPATH

This seems like vscode-go ought to build this cleanly. go build from within the src directory builds without error, and produces a functional binary. I apologize in advance if I'm just missing a minor configuration, or if I've misunderstood something about go project organization, but any help/advice would be very much appreciated!

What version of Go, VS Code & VS Code Go extension are you using?

• Run go version to get version of Go
  go version go1.14.3 darwin/amd64
• Run code -v or code-insiders -v to get version of VS Code or VS Code Insiders

1.46.0
a5d1cc28bb5da32ec67e86cc50f84c67cc690321
x64

• Check your installed extensions to get the version of the VS Code Go extension
  0.14.4
• Run go env to get the go development environment details

go env                               
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/kevin/Library/Caches/go-build"
GOENV="/Users/kevin/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/kevin/code/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.14.3/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.14.3/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
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=/var/folders/h8/t6j1zhv57x97tdzs7rs0g2_h0000gn/T/go-build368033781=/tmp/go-build -gno-record-gcc-switches -fno-common"

Share the Go related settings you have added/edited

    "go.buildOnSave": "workspace",
    "go.formatTool": "goimports"

[stamblerre]

I think you probably want to create a directory below GOPATH/src and put your project in there. It also seems like you intend to be in module mode, but the go command is looking on your GOPATH, so make sure that the GO111MODULE environment variable is not set to off.

Some additional resources are linked in our GOPATH and modules documentation.

[kkuchta]

Thanks for the reply! My go env seems to have GO111MODULE set to "" by default. I think, from my reading of the docs, that for new go versions, this should default to having module mode on. Just to be sure, I set go env -w GO111MODULE=on - that changes the error message to:
go: cannot find main module; see 'go help modules', still on the package main line.

I'm not sure I understand the bit about having this project be under GOPATH/src - shouldn't using a module remove the need to worry about the GOPATH? I've read through the linked docs on modules, but it mostly discusses which tools don't support modules - it seems like basic building should work still?

One new wrinkle: I currently have both the files for this project at project_name/src/foo.bar. If I move them to the root level of the project (so just project_name/foo.bar, the project builds cleanly. Is there something about having an src folder that vscode-go doesn't like?

[hyangah]

I noticed the unusual _ prefix in the go build target.

/usr/local/bin/go build _/Users/kevin/code/go/modtest/src

The go build target is determined by getNonVendorPackages, which retrieves the information by running go list -f 'ImportPath: {{.ImportPath}} FolderPath: {{.Dir}}' ./....

Can you try to run the go list command from the integrated terminal?
go list -f 'ImportPath: {{.ImportPath}} FolderPath: {{.Dir}}' ./...

The ImportPath will include the _ prefix if go.mod file does not exist.
go: cannot find main module also indicates that the go command couldn't find go.mod file.

Is the go.mod file saved?

You can also check whether the go command saw your go.mod file, by running go env GOMOD

[kkuchta]

$ go list -f 'ImportPath: {{.ImportPath}} FolderPath: {{.Dir}}' ./...
go: warning: "./..." matched no packages

$ go env GOMOD
/dev/null

So yeah, it seems like it's not picking up the go.mod file (which, I double-checked, is saved). If I cd into the src folder first, we get results that look more reasonable:

$ cd src
$ go list -f 'ImportPath: {{.ImportPath}} FolderPath: {{.Dir}}' ./...
ImportPath: whatever FolderPath: /Users/kevin/code/go/modtest/src
$ go env GOMOD                                                       
/Users/kevin/code/go/modtest/src/go.mod

It seems like maybe vscode-go isn't able to detect a go.mod that's not at the root level of the project?

[stamblerre]

Yep, that's explained a bit more here: golang/go#36899. Does VS Code Go work when you open it from the module root (directory containing the go.mod)?

[kkuchta]

Ah, thanks for that link - that's some useful context. That said, it looks like that only applies to gopls, and I have the "Use Language Server" setting disabled for the vscode-go extension. Presumably that means that link doesn't apply to this situation?

(Yes, opening vs code from the module root seems to work)

[hyangah]

That's go command's limitation as well - the go command is sensitive to in which directory the go command runs. As the messages in the output channel indicated, the error occurred while building the package in the workspace, and from the workspace, the go command doesn't see the packages under the nested module directory. :-(

[hyangah]

Closing this in favor of the pinned issue #275.