Build error on recent go versions (go: cannot find main module, but found .git/config), with workaround

[juozaspo]

Trying to build on Ubuntu 22.04 LTS I get an error when building using go 1.18.1.
Build log using custom build script:

go clean
go build -ldflags "-X main.Version=4 -X main.Build=`git describe --tags --always`" -o mtmapprune
go: cannot find main module, but found .git/config in /home/juozas/mtmapprune
	to create a module there, run:
	go mod init
make: *** [Makefile:11: mtmapprune] Error 1

Script contents:

#!/bin/bash
# custom build script made by juozaspo, workaround for minetest-tools/mtmapprune#1
make clean
GOPATH=/usr/share/gocode make

Running go mod init github.com/minetest-tools/mtmapprune succeeds but then build fails with error go: could not create module cache: mkdir /usr/share/gocode/pkg: permission denied unless I change the go path. Also the global path in /usr/share/gocode cannot be used as build process tries to write there, and the building takes more time than expected, sqlite library must be installed using command go get github.com/mattn/go-sqlite3.

golang-go package is installed, golang-github-mattn-go-sqlite3-dev appears to be no longer needed, also the readme does not describe what other dependencies are needed, also there are a few new files created by commands above (go mod init, go get), for now I've added them to .gitignore on my fork.

$ cat go.mod 
module github.com/minetest-tools/mtmapprune

go 1.18

require github.com/mattn/go-sqlite3 v1.14.15 // indirect
$ cat go.sum 
github.com/mattn/go-sqlite3 v1.14.15 h1:vfoHhTN1af61xCRSWzFIWzx2YskyMTwHLrExkBOjvxI=
github.com/mattn/go-sqlite3 v1.14.15/go.mod h1:2eHXhiwb8IkHr+BDWZGa96P6+rkvnG63S2DGjv9HUNg=

My updated fork: https://github.com/juozaspo/mtmapprune, with default branch set to testing, with go path removed from build script