version/mkversion: open-source version generation logic

In preparation for moving more of the release building here too.

Signed-off-by: David Anderson <danderson@tailscale.com>

cmd/mkversion/mkversion.go

@@ -0,0 +1,44 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// mkversion gets version info from git and outputs a bunch of shell variables
+// that get used elsewhere in the build system to embed version numbers into
+// binaries.
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"time"
+
+	"tailscale.com/tailcfg"
+	"tailscale.com/version/mkversion"
+)
+
+func main() {
+	prefix := ""
+	if len(os.Args) > 1 {
+		if os.Args[1] == "--export" {
+			prefix = "export "
+		} else {
+			fmt.Println("usage: mkversion [--export|-h|--help]")
+			os.Exit(1)
+		}
+	}
+
+	var b bytes.Buffer
+	io.WriteString(&b, mkversion.Info().String())
+	// Copyright and the client capability are not part of the version
+	// information, but similarly used in Xcode builds to embed in the metadata,
+	// thus generate them now.
+	copyright := fmt.Sprintf("Copyright © %d Tailscale Inc. All Rights Reserved.", time.Now().Year())
+	fmt.Fprintf(&b, "VERSION_COPYRIGHT=%q\n", copyright)
+	fmt.Fprintf(&b, "VERSION_CAPABILITY=%d\n", tailcfg.CurrentCapabilityVersion)
+	s := bufio.NewScanner(&b)
+	for s.Scan() {
+		fmt.Println(prefix + s.Text())
+	}
+}