go/build: Default does not honor `go env -w GOPATH`

[heschi]

go/build has no logic for reading the GOENV file, so it will ignore any GOPATH setting there.

go/src/go/build/build.go

Lines 275 to 292 in 7eb5941

	func defaultGOPATH() string {
	env := "HOME"
	if runtime.GOOS == "windows" {
	env = "USERPROFILE"
	} else if runtime.GOOS == "plan9" {
	env = "home"
	}
	if home := os.Getenv(env); home != "" {
	def := filepath.Join(home, "go")
	if filepath.Clean(def) == filepath.Clean(runtime.GOROOT()) {
	// Don't set the default GOPATH to GOROOT,
	// as that will trigger warnings from the go tool.
	return ""
	}
	return def
	}
	return ""
	}

[gopherbot]

Change https://golang.org/cl/239754 mentions this issue: all: rework goimports environment, support GOMODCACHE

[mvdan]

Since build.Default is a global variable, wouldn't a call to go env add quite a lot of cost to the init function?

[heschi]

Definitely, 20ms at least. I was assuming that it would directly open and parse the config file.

[mvdan]

Gotcha - I assume that is acceptable, given that go/build and cmd/go are released together.