main: use `go env` instead of doing all detection manually

This replaces our own manual detection of various variables (GOROOT,
GOPATH, Go version) with a simple call to `go env`.

If the `go` command is not found:

    error: could not find 'go' command: executable file not found in $PATH

If the Go version is too old:

    error: requires go version 1.18 through 1.20, got go1.17

If the Go tool itself outputs an error (using GOROOT=foobar here):

    go: cannot find GOROOT directory: foobar

This does break the case where `go` wasn't available in $PATH but we
would detect it anyway (via some hardcoded OS-dependent paths). I'm not
sure we want to fix that: I think it's better to tell users "make sure
`go version` prints the right value" than to do some automagic detection
of Go binary locations.

1 files changed, 1 insertions, 1 deletions

diff --git a/main.go b/main.go
index a6a16f92d..7af036f17 100644
--- a/main.go
+++ b/main.go
@@ -1871,7 +1871,7 @@ func main() {
 		usage(command)
 	case "version":
 		goversion := "<unknown>"
-		if s, err := goenv.GorootVersionString(goenv.Get("GOROOT")); err == nil {
+		if s, err := goenv.GorootVersionString(); err == nil {
 			goversion = s
 		}
 		version := goenv.Version