How do you call a Go function in VSCode? - go

Question

I have VSCode and the Go plugin installed. I am trying to call this function:
package main
import "fmt"
func printHello() {
fmt.Println("hello world")
}
First, I opened the VSCode Command Palette and chose Go: Test file, which threw a No tests found. Current file is not a test file. error.
Then I opened the VSCode Command Palette and chose Go: Test function at cursor - this threw the same error.
Then I created a sibling file with a _test.go naming convention:
package main
import (
"testing"
)
func TestHello(t *testing.T) {
msg, err := printHello()
}
This threw a build error: c:\path\to\my_test.go:8:18: main() used as value.
Then I added a simple return statement, which threw the following error:
go: cannot find main module, but found .git/config in c:\path\to\my_folder
to create a module there, run:
cd ..\.. && go mod init
I right-clicked the function name itself and chose the Go: Debug Test at Cursor function, and the Go: Generate unit tests for function option, which in-turn prompted me to install several other VSCode plugins, and prompted me to upgrade Go itself. The previous two Command Palette options started to fail with ENOENT errors, so I restarted VSCode, and got a new test function. I opened up the VSCode Debug Console but it wouldn't let me start a session there.
I right-clicked the parent folder and chose the Open in Integrated Terminal option, which started a WSL session - cd ..\.. && go mod init threw errors related to GOPATH:
me#COMPUTER:/mnt/c/path/to/my_folder$ go mod init
-bash: /c/go/bin/go.exe: No such file or directory
I tried determining what the WSL GOPATH was pointing to via Go: Show current GOPATH - it actually turned out that both the WSL and VSCode GOPATHs were incorrect.
I opened up a normal Command Prompt which had the correct GOPATH and I fired off go mod init which errored out (the previous guidance from VSCode was incorrect):
go: cannot determine module path for source directory C:\path\to\my_folder (outside GOPATH, module path must be specified)
Example usage:
'go mod init example.com/m' to initialize a v0 or v1 module
'go mod init example.com/m/v2' to initialize a v2 module
Run 'go help mod init' for more information.
I decided on a v2 Go module initialization (I don't know why one would opt for v0 or v1), which created a go.mod in the root directory of my project, but now I am seeing the following package-related errors:
gopls requires a module at the root of your workspace.
You can work with multiple modules by opening each one as a workspace folder.
Improvements to this workflow will be coming soon, and you can learn more here:
https://github.com/golang/tools/blob/master/gopls/doc/workspace.md.
How do I call a Go function in VSCode?

Answer 1

The answer turns out to be:
You need to create a *_test.go unit test harness and install more adjacent VSCode plugins.
You need to run go mod init blah somewhere outside of VSCode. blah is the name of your module. VSCode is unreliable with respect to the GOPATH.
There is a gotcha here where if you run go mod init main, this is valid but VSCode will throw misleading errors later on (see https://appliedgo.net/testmain/). You have to name it something else.
You need to re-open the VSCode workspace in a way such that go.mod is in the root of the workspace, or else VSCode runs into relative pathing errors.