feat(deps): add support for Nix package manager (#116)

This serves as an alternative to Homebrew. It should be much more stable
and cause less headaches over time for automated builds.

There should be no change to the end user experience of using the build
script, as it should still work with and use Homebrew by default.

Additionally, Nix provides older Apple SDKs, allowing us to run against
macOS 11.x SDKs. This allows the resulting Emacs.app builds to be
compatible with macOS 11.x and later versions.

In testing, this seems to be the case on macOS 11.x (x86_64) and macOS
12.x (arm64).

pkg/dmgbuild/license.go

@@ -116,7 +116,6 @@ func NewLicense() License {
 	return License{}
 }
 
-//nolint:goconst
 func (s *License) Render() []string {
 	var l []string
 

pkg/osinfo/osinfo.go

@@ -1,41 +1,65 @@
 package osinfo
 
 import (
+	"os"
 	"os/exec"
 	"strconv"
 	"strings"
 )
 
 type OSInfo struct {
-	Name    string `yaml:"name" json:"name"`
-	Version string `yaml:"version" json:"version"`
-	Arch    string `yaml:"arch" json:"arch"`
+	Name       string `yaml:"name" json:"name"`
+	Version    string `yaml:"version" json:"version"`
+	SDKVersion string `yaml:"sdk_version" json:"sdk_version"`
+	Arch       string `yaml:"arch" json:"arch"`
 }
 
 func New() (*OSInfo, error) {
-	version, err := exec.Command("sw_vers", "-productVersion").CombinedOutput()
+	version, err := exec.Command("sw_vers", "-productVersion").Output()
 	if err != nil {
 		return nil, err
 	}
 
+	sdkVersion := os.Getenv("MACOSX_DEPLOYMENT_TARGET")
+	if sdkVersion == "" {
+		var ver []byte
+		ver, err = exec.Command("xcrun", "--show-sdk-version").Output()
+		if err != nil {
+			return nil, err
+		}
+
+		sdkVersion = string(ver)
+	}
+
 	arch, err := exec.Command("uname", "-m").CombinedOutput()
 	if err != nil {
 		return nil, err
 	}
 
 	return &OSInfo{
-		Name:    "macOS",
-		Version: strings.TrimSpace(string(version)),
-		Arch:    strings.TrimSpace(string(arch)),
+		Name:       "macOS",
+		Version:    strings.TrimSpace(string(version)),
+		SDKVersion: strings.TrimSpace(sdkVersion),
+		Arch:       strings.TrimSpace(string(arch)),
 	}, nil
 }
 
-// DistinctVersion returns macOS version down to a distinct "major"
-// version. For macOS 10.x, this will include the first two numeric parts of the
-// version (10.15), while for 11.x and later, the first numeric part is enough
-// (11).
+// DistinctVersion returns macOS version down to a distinct "major" version. For
+// macOS 10.x, this will include the first two numeric parts of the version
+// (10.15), while for 11.x and later, the first numeric part is enough (11).
 func (s *OSInfo) DistinctVersion() string {
-	parts := strings.Split(s.Version, ".")
+	return s.distinctVersion(s.Version)
+}
+
+// DistinctSDKVersion returns macOS version down to a distinct "major" version.
+// For macOS 10.x, this will include the first two numeric parts of the version
+// (10.15), while for 11.x and later, the first numeric part is enough (11).
+func (s *OSInfo) DistinctSDKVersion() string {
+	return s.distinctVersion(s.SDKVersion)
+}
+
+func (s *OSInfo) distinctVersion(version string) string {
+	parts := strings.Split(version, ".")
 
 	if n, _ := strconv.Atoi(parts[0]); n >= 11 {
 		return parts[0]

pkg/plan/create.go

@@ -95,10 +95,17 @@ func Create(ctx context.Context, opts *Options) (*Plan, error) { //nolint:funlen
 		releaseName = "Emacs." + version
 	}
 
+	// Attempt to get the macOS SDK version from the environment, if it's not
+	// available, use the version from the system.
+	targetMacOSVersion := osInfo.DistinctSDKVersion()
+	if targetMacOSVersion == "" {
+		targetMacOSVersion = osInfo.DistinctVersion()
+	}
+
 	buildName := fmt.Sprintf(
 		"Emacs.%s.%s.%s",
 		absoluteVersion,
-		sanitize.String(osInfo.Name+"-"+osInfo.DistinctVersion()),
+		sanitize.String(osInfo.Name+"-"+targetMacOSVersion),
 		sanitize.String(osInfo.Arch),
 	)
 	diskImage := buildName + ".dmg"

pkg/sign/emacs.go

@@ -123,7 +123,7 @@ func signCLIHelper(ctx context.Context, appBundle string, opts *Options) error {
 // app bundle itself.
 func elnFiles(emacsApp string) ([]string, error) {
 	var files []string
-	walkDirFunc := func(path string, d fs.DirEntry, _err error) error {
+	walkDirFunc := func(path string, d fs.DirEntry, _ error) error {
 		if d.Type().IsRegular() && strings.HasSuffix(path, ".eln") &&
 			!strings.Contains(path, ".app/Contents/Frameworks/") {
 			files = append(files, path)