Go get behaving erratically during build and with VScode - go

Question

Using Go version go1.17.1 linux/amd64 on my CentOS 7. GOPATH and GOROOT are set in my .bashrc in the order:
export GOPATH="${HOME}/.go"
export GOROOT="/usr/local/go"
export PATH="$PATH:${GOPATH}/bin:${GOROOT}/bin"
Got my project in /home/wsb/_projects/local/parlance:
[wsb#localhost local]$ pwd
/home/wsb/_projects/local
[wsb#localhost local]$ tree
.
└── parlance/
└── main.go
└── utils.go
From the terminal, using go get stores src in /home/wsb/.go/pkg/mod/cache... folder
[wsb#localhost parlance]$ go get -v -u github.com/gorilla/mux
go: downloading github.com/gorilla/mux v1.8.0
github.com/gorilla/mux
[wsb#localhost parlance]$ go build main.go
main.go:3:8: no required module provides package github.com/gin-gonic/gin: go.mod file not found in current directory or any parent directory; see 'go help modules'
[wsb#localhost parlance]$
[root#localhost /]# find -iname gin
./home/wsb/.go/pkg/mod/cache/download/github.com/gin-gonic/gin
Why would it throw error on build?

Answer 1

Using go mod is the key here for managing packages for any particular projects.
go mod is used for installing and tracking external packages outside of packages in GOPATH.
From within existing project root directory parlance we initialize go mod using:
[wsb#localhost parlance]$ go mod parlance
It creates two files within the project root directory: go.mod and go.sum.
Now we can go get any module we will use specifically for our project.
go get github.com/gin-gonic/gin
go get github.com/gofiber/fiber/v2
This creates external package requirement details in go.mod and their respective checksum in go.sum file.
Finally, we can build/run our package like
go build main.go
go run main.go