Why does debugging Go with VS Code and WSL hang Delve?

I am trying to debug a Go program in VS Code, using WSL. The program compiles and runs, but when trying to debug with dlv dap, it seems to hang and never reach the first breakpoint. I am using go 1.17, dlv 1.7.2 and Ubuntu 20.04. The problem is replicated with the simple Hello World program:

package main

import "fmt"

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

If I chose Run->Run Without Debugging, the Debug Consol shows

> Starting: /mnt/f/mattm/home/go/bin/dlv-dap dap
> --check-go-version=false --only-same-user=false --listen=127.0.0.1:53252 --log=true --log-output=rpc --log-dest=3 from /mnt/f/mattm/home/hw <br>DAP server listening at: 127.0.0.1:53252 <br>
> hello world <br>
> Process 17851 has exited with status 0 dlv dap (17754) exited with code: 0

The program has run and exited successfully (though why start dlv if not debugging?) But if I try to Run->Start Debugging, the console window only shows:

> Starting: /mnt/f/mattm/home/go/bin/dlv-dap dap
> --check-go-version=false --only-same-user=false --listen=127.0.0.1:56084 --log=true --log-output=rpc --log-dest=3 from /mnt/f/mattm/home/hw <br> DAP server listening at: 127.0.0.1:56084

The program does not appear to execute, VS Code never shows execution reaching a breakpoint. (The outcome is the same whether or not I've set breakpoints). Task Manager does show a dlv-dap process running; it appears to be hung and waiting for something. But what? If I terminate debugging under VS Code, the dlv-dap process remains. It is as though VS Code spun off the dlv process and then forgotten about it. Do I need to prompt VS Code to connect to the DAP server to proceed? How do I do that?

Addendum:
I am using the following launch configuration:

"name": "Launch Package",
"type": "go",
"request": "launch",
"mode": "debug",
"program": "${fileDirname}",
"logOutput": "dap,debugger",
"showLog": true,
"dlvFlags" : ["--only-same-user=false"]

After turning on verbose dlv logging (as in the config above), I get the following:

> Starting: /mnt/f/mattm/home/go/bin/dlv-dap dap
> --check-go-version=false --only-same-user=false --listen=127.0.0.1:51444 --log=true --log-output=dap,debugger --log-dest=3 from /mnt/f/mattm/home/breezepms/hello-world DAP server listening at: 127.0.0.1:51444 2021-10-17T16:35:27+01:00 debug
> layer=dap DAP server pid = 7019 2021-10-17T16:35:27+01:00 debug
> layer=dap DAP connection started 2021-10-17T16:35:27+01:00 debug
> layer=dap [<- from
> client]{"seq":1,"type":"request","command":"initialize","arguments":{"clientID":"vscode","clientName":"Visual
> Studio
> Code","adapterID":"go","locale":"en-gb","linesStartAt1":true,"columnsStartAt1":true,"pathFormat":"path","supportsVariableType":true,"supportsVariablePaging":true,"supportsRunInTerminalRequest":true,"supportsMemoryReferences":true,"supportsProgressReporting":true,"supportsInvalidatedEvent":true}}
> 2021-10-17T16:35:27+01:00 debug layer=dap [-> to
> client]{"seq":0,"type":"response","request_seq":1,"success":true,"command":"initialize","body":{"supportsConfigurationDoneRequest":true,"supportsFunctionBreakpoints":true,"supportsConditionalBreakpoints":true,"supportsEvaluateForHovers":true,"supportsSetVariable":true,"supportsExceptionInfoRequest":true,"supportTerminateDebuggee":true,"supportsDelayedStackTraceLoading":true,"supportsLogPoints":true,"supportsClipboardContext":true,"supportsSteppingGranularity":true}}
> 2021-10-17T16:35:27+01:00 debug layer=dap [<- from
> client]{"seq":2,"type":"request","command":"launch","arguments":{"name":"Launch
> file","type":"go","request":"launch","mode":"debug","program":"./hello-world.go","logOutput":"dap,debugger","showLog":true,"dlvFlags":["--only-same-user=false"],"__configurationTarget":5,"packagePathToGoModPathMap":{"/mnt/f/mattm/home/breezepms/web/xmlutilities":"/mnt/f/mattm/home/breezepms/web/xmlutilities","/mnt/f/mattm/home/breezepms/ledgers":"/mnt/f/mattm/home/breezepms/ledgers","/mnt/f/mattm/home/breezepms/web":"/mnt/f/mattm/home/breezepms","/mnt/f/mattm/home/breezepms/web/filehandling":"/mnt/f/mattm/home/breezepms/web/filehandling","/mnt/f/mattm/home/breezepms/persistence":"/mnt/f/mattm/home/breezepms/persistence","/mnt/f/mattm/home/breezepms/cmd/csvloader":"/mnt/f/mattm/home/breezepms","/mnt/f/mattm/home/breezepms/hello-world":"/mnt/f/mattm/home/breezepms"},"debugAdapter":"dlv-dap","apiVersion":2,"dlvLoadConfig":{"followPointers":true,"maxVariableRecurse":1,"maxStringLen":64,"maxArrayValues":64,"maxStructFields":-1},"showGlobalVariables":false,"substitutePath":[],"dlvToolPath":"/mnt/f/mattm/home/go/bin/dlv-dap","env":{},"__buildDir":"/mnt/f/mattm/home/breezepms/hello-world","__sessionId":"8e201eb7-88ec-452f-896d-3d5e98596c05"}}
> 2021-10-17T16:35:27+01:00 debug layer=dap debug backend is 'default'
> 2021-10-17T16:35:27+01:00 debug layer=dap building program
> './hello-world.go' in '/mnt/f/mattm/home/breezepms/hello-world' with
> flags '' 2021-10-17T16:35:29+01:00 debug layer=dap running binary
> '/tmp/__debug_bin3449446367' in '.' 2021-10-17T16:35:29+01:00 info
> layer=debugger launching process with args:
> [/tmp/__debug_bin3449446367]

The comments above helped me find a solution. The problem wasn't in VS Code itself, rather underlying dlv was unable to function properly. There is some documentation of the issue around the Internet https://github.com/microsoft/WSL/issues/2977. dlv does not work in WSL 1. Though I thought I had upgraded to WSL 2, I had not upgraded my Ubuntu installation to WLS 2. After re-installing Ubuntu 20.04 under WSL 2, (and reinstalling go and dlv) I was able to debug from VS Code.

I think I'm coming late but anyway, it's not possible to get delve working on WSL, but since WSL2 become avaliable now you can.

In my case I could do it by following these steps:

1- Install Delve inside WSL 2 (Or remote host)

go install github.com/go-delve/delve/cmd/dlv@latest

2- Compile and launch my application with the following flag (-gcflags "all=-N -l") to allow Delve to collect advanced debugging information. E.g. :

go run cmd/server/main.go -gcflags "all=-N -l"

3- To debug inside WLS 2, I first had to run a headless Delve server by running:

dlv debug cmd/server/main.go --headless --listen=:2345 --log --api-version=2

4- Setup the launch.json in VSCode

...
{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Example Debug WSL2",
            "type": "go",
            "debugAdapter": "dlv-dap",
            "request": "attach",
            "mode": "remote",
            "remotePath": "${workspaceFolder}",
            "port": 2345,
            "host": "127.0.0.1"
        }
    ]
}
...

Here are some useful documentation for furthermore details.

https://github.com/golang/vscode-go/blob/master/docs/debugging.md#remote-debugging

https://go.googlesource.com/vscode-go/+/refs/heads/dev.go2go/docs/debugging.md

https://jerome-ran.medium.com/golang-remote-debugging-with-visual-studio-code-a918de5d83f3

These links saved my life, hope this helps.

I went through hell with my vscode debug configuration using delve under wsl2 and vscode studio under windows 10. Thanks to @Potemkin post here for giving me the first insights to this topic.

Here is my working configuration:

1. Install delve debug server in wsl2:

git clone https://github.com/go-delve/delve
cd delve
go install github.com/go-delve/delve/cmd/dlv

See: https://github.com/go-delve/delve/tree/master/Documentation/installation#installation

PS: If your GOBIN directory isnt in your PATH variable referenced, you have to execute the dlv binary by using the absolute path: $HOME/go/bin/dlv

2. Run delve debug server in wsl2:

cd <your-golang-project>
dlv debug ./main.go --headless --listen=127.0.0.1:12345 --accept-multiclient --continue --only-same-user=false

The only-same-user parameter is very important when you are using wsl2 and windows cause otherwise you could end up having this error message: closing connection from different user (127.0.0.1:34406): connections to localhost are only accepted from the same UNIX user for security reasons.

Furthermore without stating explicitly the 127.0.0.1 loopback adress in the listen parameter it wasnt working for me (just using
listen=:12345 didnt worked)!

Further information about remote debugging with delve and vscode you will find here: https://github.com/golang/vscode-go/blob/master/docs/debugging.md#remote-debugging

3. Use this launch.json in run and debug tab in vscode studio and start debugging:

    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Example Debug WSL2",
            "type": "go",
            "request": "attach",
            "mode": "remote",
            "port": 12345,
            "host": "127.0.0.1"
        }
    ]
}

I also tried to use the "debugAdapter": "dlv-dap" configuration in my launch.json, but that ended up with the error message "could not find file..." when reaching a breakpoint. With the default legacy debugAdapeter as used with the config stated above it works fine.