golang dlv unable to see source:: no such file or directory - delve

Question

In a docker container:
docker run \
--rm -it \
-p 80:80 \
-p 2345:2345 \
-v $(pwd)/src:/go/src/ \
--security-opt="seccomp=unconfined" \
--privileged \
--cap-add SYS_PTRACE \
golang bash
In the container at $GOPATH:
go get -u github.com/derekparker/delve/cmd/dlv
dlv version
Delve Debugger
Version: 1.1.0
Build: $Id: 1990ba12450cab9425a2ae62e6ab988725023d5c
dlv debug app --headless --listen=0.0.0.0:2345 --api-version=2
In mac terminal at $GOPATH::
dlv version
Delve Debugger
Version: 1.1.0
Build: $Id: 1990ba12450cab9425a2ae62e6ab988725023d5c $
dlv connect 127.0.0.1:2345
I get the following, but unable to list source?
dlv connect 127.0.0.1:2345
Type 'help' for list of commands.
(dlv) b main.go:29
Breakpoint 1 set at 0x7f584d for main.main.func1() /go/src/app/main.go:29
(dlv) c
> main.main.func1() /go/src/app/main.go:29 (hits goroutine(4):1 total:1) (PC: 0x7f584d)
(dlv) l
> main.main.func1() /go/src/app/main.go:29 (hits goroutine(4):1 total:1) (PC: 0x7f584d)
Command failed: open /go/src/app/main.go: no such file or directory
Note: I am in $GOPATH in both the dlv server and client:
In container:
ls $GOPATH/src/app
layout.html main.go mypack
In mac terminal:
ls $GOPATH/src/app
layout.html main.go mypack
vs code launch.json:
{
// Use IntelliSense to learn about possible attributes.
// Hover to view descriptions of existing attributes.
// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
"version": "0.2.0",
"configurations": [
{
"name": "Connect to server",
"type": "go",
"request": "launch",
"mode": "remote",
"remotePath": "${workspaceFolder}",
"port": 2345,
"host": "127.0.0.1",
"program": "${workspaceFolder}",
"env": {},
"args": [],
"trace": "verbose"
},
]
}

Answer 1

See https://github.com/go-delve/delve/issues/1438. Solution is to put this in
$HOME/.dlv/config.yml:
substitute-path:
- {from: /, to: /root}

Answer 2

On my Ubuntu 18.04 I see the location of the file as ~/.config/dlv/config.yml. Here is an example:
substitute-path:
- {from: /code, to: /home/foo/git/repo}

Answer 3

I wanted to add to the answers above that you do not necessarily need to create a config.yaml file to set substitute-path, you can also do so from inside dlv shell by running: config substitute-path / /root