debug: delve dap launch mode fails without go.mod

[hyangah]

dlv built from the master (3fd78fc)
go version 1.15.3

package main
  
func main() {
  println("hello")
}

and there is no go.mod file.

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Launch (delve DAP)",
            "type": "godlvdap",
            "request": "launch",
            "mode": "auto",
            "program": "${fileDirname}",
            "env": {},
            "args": [],
            "logOutput": "dap",
            "showLog": true,
            "trace": "verbose"
        }
    ]
}

Verbose logs are written to:
/var/folders/bw/6r6k9d113sv1_vvzk_1kfxbm001py5/T/vscode-godlvdapdebug.txt
2020-11-2, 17:03:26.632 UTC
From client: initialize({"clientID":"vscode","clientName":"Visual Studio Code","adapterID":"godlvdap","pathFormat":"path","linesStartAt1":true,"columnsStartAt1":true,"supportsVariableType":true,"supportsVariablePaging":true,"supportsRunInTerminalRequest":true,"locale":"en-us","supportsProgressReporting":true,"supportsInvalidatedEvent":true})
InitializeRequest
To client: {"seq":0,"type":"response","request_seq":1,"command":"initialize","success":true,"body":{"supportsConfigurationDoneRequest":true}}
InitializeResponse
From client: launch({"name":"Launch (delve DAP)","type":"godlvdap","request":"launch","mode":"debug","program":"/Users/hakim/tmp/scale","env":{"ELECTRON_RUN_AS_NODE":"1","USER":"hakim","PATH":...]
launchRequest
Running: /Users/hakim/go/bin/dlv dap --listen=127.0.0.1:42042 --log=true --log-output=dap
dlv stdout: DAP server listening at: 127.0.0.1:42042
dlv stderr: 2020-11-02T12:03:26-05:00 debug layer=dap DAP server pid = 8743
dlv stderr: 2020-11-02T12:03:26-05:00 debug layer=dap [<- from client]{"seq":2,"type":"request","command":"launch","arguments":{"__sessionId":"c116f53e-ee2d-47c8-96fa-f34b3933b335","apiVersion":2,"args":[],"dlvLoadConfig":{"followPointers":true,"maxArrayValues":64,"maxStringLen":64,"maxStructFields":-1,"maxVariableRecurse":1},"dlvToolPath":"/Users/hakim/go/bin/dlv","env":{[...]
dlv stderr: import "/Users/hakim/tmp/scale": cannot import absolute path
dlv stderr: 2020-11-02T12:03:27-05:00 error layer=dap Failed to launch: Build error: exit status 1
dlv stderr: 2020-11-02T12:03:27-05:00 debug layer=dap [-> to client]{"seq":0,"type":"response","request_seq":2,"success":false,"command":"launch","message":"Failed to launch","body":{"error":{"id":3000,"format":"Failed to launch: Build error: exit status 1"}}}
To client: {"seq":0,"type":"response","request_seq":2,"success":false,"command":"launch","message":"Failed to launch","body":{"error":{"id":3000,"format":"Failed to launch: Build error: exit status 1"}}}

See the error import "/Users/hakim/tmp/scale": cannot import absolute path.
Not sure yet what's the expected behavior in this case (where no go.mod file exists and the directory is outside GOPATH).
go build, dlv debug, and old debug adapter seem ok with it.

[hyangah]

cc @polinasok

[hyangah]

The build error is because the 'program' attribute is the absolute path to the target package directory (${fileDirname}), and
gobuild.GoBuild with the directory path fails. The same build failure can be observed if we run dlv debug /Users/hakim/tmp/scale or go build /Users/hakim/tmp/scale without go.mod.

The old debug adapter avoids this issue because it launches dlv debug without specifying target; dlv implicitly assumes the package in the current working directory is the target. The below is the trace from the old debug adapter.

Current working directory: /Users/hakim/tmp/scale
Running: /Users/hakim/go/bin/dlv debug --headless=true --listen=127.0.0.1:6459 --api-version=2 --log=true --log-output=dap

Do we need to do the same in dlv dap: if program is a directory, build from the program directory without passing the program?

cc @polinasok @suzmue

[hyangah]

With go1.16 and the latest delve (master), the error message is descriptive enough.

Build Error: go build -o /Users/hakim/projects/demo/__debug_bin -gcflags all=-N -l /Users/hakim/projects/demo
go: go.mod file not found in current directory or any parent directory; see 'go help modules' (exit status 1)

And if I disable go modules explicitly (GO111MODULE=off), this also works.

Users are supposed to set up the go.mod correctly or configure the 'program' attribute correctly.
I don't see anything that needs to be done further from dlv dap side or extension side. Closing.