go/src/cmd/go/internal/base/tool.go

// Tool returns the path to the named tool (for example, "vet").
// If the tool cannot be found, Tool exits the process.
func Tool(toolName string) string { … }

// ToolPath returns the path at which we expect to find the named tool
// (for example, "vet"), and the error (if any) from statting that path.
func ToolPath(toolName string) (string, error) { … }

var toolStatCache …