! go mod tidy
stderr '^go: warning: ignoring go.mod in \$GOPATH'
stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules'''

go env
stdout 'GOPATH='
stderr '^go: warning: ignoring go.mod in \$GOPATH'

-- $GOPATH/go.mod --
module bug

go 1.21