https://golang.org/doc/go1.16
Module-aware mode is enabled by default, regardless of whether a go.mod file is present in the current working directory or a parent directory. More precisely, the GO111MODULE environment variable now defaults to on. To switch to the previous behavior, set GO111MODULE to auto.
Build commands like go build and go test no longer modify go.mod and go.sum by default. Instead, they report an error if a module requirement or checksum needs to be added or updated (as if the -mod=readonly flag were used). Module requirements and sums may be adjusted with go mod tidy or go get.
