go: cannot find main module, but found .git config to create a module there, run: go mod

go: cannot find main module, but found .git/config to create a module there, run: go mod

This problem occurred in a monorepo opened in VSCode. The repo has many services placed in isolated directories with respective go.mod files.

I realized from various sources that the problem is from two places:

1. Move the mono repo under $GOPATH/src.
2. The ~/.zshrc or ~/.bashrc must be as follows:

   export GOPATH=$HOME/go/
   export GOROOT=/usr/local/go
   
   export PATH="$GOROOT/bin:$PATH"
   export PATH="$PATH:$GOPATH/bin"
   

Do not add any other variable that affects gopls such as GO111MODULE=on.

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References