I have a go thing I wrote that I hadn't touched for years but had the misfortune to need to modify it recently, and the way to migrate from $GOPATH/src/ to go.mod is not really clear (to me at least). To build this thing, the only go code I have, I used git submodules to put all the dependencies in ./src, so I had ./src/github.com and a load of 3rd party modules in there, then my code was in ./src/Mything. To build it, I ran "env GOPATH=$PWD go build Mything/MyPackage" and it did the right thing, with the final binary appearing in the current directory.
Now this gives an error "go.mod file not found in current directory", but if I add that file, go build says "unexpected go.mod file found in current directory".
Luckily, for now, I can use GO111MODULE=off to keep pretending everything is fine, but my eyes start to glaze over when I read the migration guide at https://go.dev/blog/migrating-to-go-modules - it's one of those moments where I start to wish I'd used a different language :(
Nah, I wish it were it that easy. There is definitely more yak shaving involved.
"go mod init" returns the error "go: cannot determine module path for source directory".
"go mod init src/mything/mypackage" creates a go.mod file, but then "env GOPATH=$PWD go build mything/mypackage" says "$GOPATH/go.mod exists but should not" (as opposed to when it isn't there, then go complains "go.mod file not found in current directory")
Note that "env GOPATH=$PWD GO111MODULE=off go build mything/mypackage" does build all the source code.
Most likely I've set the whole project and directory structure up wrong, and it only works by brute force.
it should have been `go mod init mything/mypackage` (without the `src/`) in the `GOPATH/src/mything/mypackage` directory,
and `GOPATH=$PWD` is almost certainly wrong. The `go` command in module mode assumes independence from GOPATH, so to build something, you have to be "in" the module (under a directory with a `go.mod` file).
