internal/nix: add support for Nix forks (#2091)

Increases leniency for `nix --version` output to support Nix forks, such
as Lix:

        nix (Lix, like Nix) 2.90.0-beta.1-lixpre20240506-b6799ab

Co-authored-by: Greg Curtis <[email protected]>

Author: SapphicCode

internal/nix/nix.go

@@ -191,6 +191,10 @@ const (
 	MinVersion = Version2_12
 )
 
+// versionRegexp matches the first line of "nix --version" output.
+// Semantic component sourced from https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string
+var versionRegexp = regexp.MustCompile(`^(.+) \(.+\) ((?P<major>0|[1-9]\d*)\.(?P<minor>0|[1-9]\d*)\.(?P<patch>0|[1-9]\d*)(?:-(?P<prerelease>(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+(?P<buildmetadata>[0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?)$`)
+
 // VersionInfo contains information about a Nix installation.
 type VersionInfo struct {
 	// Name is the executed program name (the first element of argv).
@@ -252,11 +256,12 @@ func parseVersionInfo(data []byte) (VersionInfo, error) {
 	}
 
 	lines := strings.Split(string(data), "\n")
-	found := false
-	info.Name, info.Version, found = strings.Cut(lines[0], " (Nix) ")
-	if !found {
+	matches := versionRegexp.FindStringSubmatch(lines[0])
+	if len(matches) < 3 {
 		return info, redact.Errorf("parse nix version: %s", redact.Safe(lines[0]))
 	}
+	info.Name = matches[1]
+	info.Version = matches[2]
 	for _, line := range lines {
 		name, value, found := strings.Cut(line, ": ")
 		if !found {

internal/nix/nix_test.go

@@ -1,3 +1,4 @@
+//nolint:dupl
 package nix
 
 import (
@@ -118,17 +119,79 @@ Data directory: /nix/store/m0ns07v8by0458yp6k30rfq1rs3kaz6g-nix-2.21.2/share
 	}
 }
 
-func TestParseVersionInfoShort(t *testing.T) {
-	info, err := parseVersionInfo([]byte("nix (Nix) 2.21.2"))
+func TestParseLixVersionInfo(t *testing.T) {
+	raw := `nix (Lix, like Nix) 2.90.0-beta.1
+System type: aarch64-darwin
+Additional system types: x86_64-darwin
+Features: gc, signed-caches
+System configuration file: /etc/nix/nix.conf
+User configuration files: /Users/nobody/.config/nix/nix.conf:/etc/xdg/nix/nix.conf
+Store directory: /nix/store
+State directory: /nix/var/nix
+Data directory: /nix/store/12asl5a17ffj78njcy2fj31v59rdmanx-lix-2.90-beta.1/share
+`
+
+	info, err := parseVersionInfo([]byte(raw))
 	if err != nil {
 		t.Error("got parse error:", err)
 	}
 	if got, want := info.Name, "nix"; got != want {
 		t.Errorf("got Name = %q, want %q", got, want)
 	}
-	if got, want := info.Version, "2.21.2"; got != want {
+	if got, want := info.Version, "2.90.0-beta.1"; got != want {
 		t.Errorf("got Version = %q, want %q", got, want)
 	}
+	if got, want := info.System, "aarch64-darwin"; got != want {
+		t.Errorf("got System = %q, want %q", got, want)
+	}
+	if got, want := info.ExtraSystems, []string{"x86_64-darwin"}; !slices.Equal(got, want) {
+		t.Errorf("got ExtraSystems = %q, want %q", got, want)
+	}
+	if got, want := info.Features, []string{"gc", "signed-caches"}; !slices.Equal(got, want) {
+		t.Errorf("got Features = %q, want %q", got, want)
+	}
+	if got, want := info.SystemConfig, "/etc/nix/nix.conf"; got != want {
+		t.Errorf("got SystemConfig = %q, want %q", got, want)
+	}
+	if got, want := info.UserConfigs, []string{"/Users/nobody/.config/nix/nix.conf", "/etc/xdg/nix/nix.conf"}; !slices.Equal(got, want) {
+		t.Errorf("got UserConfigs = %q, want %q", got, want)
+	}
+	if got, want := info.StoreDir, "/nix/store"; got != want {
+		t.Errorf("got StoreDir = %q, want %q", got, want)
+	}
+	if got, want := info.StateDir, "/nix/var/nix"; got != want {
+		t.Errorf("got StateDir = %q, want %q", got, want)
+	}
+	if got, want := info.DataDir, "/nix/store/12asl5a17ffj78njcy2fj31v59rdmanx-lix-2.90-beta.1/share"; got != want {
+		t.Errorf("got DataDir = %q, want %q", got, want)
+	}
+}
+
+func TestParseVersionInfoShort(t *testing.T) {
+	cases := []struct {
+		in      string
+		name    string
+		version string
+	}{
+		{"nix (Nix) 2.21.2", "nix", "2.21.2"},
+		{"command (Nix) name (Nix) 2.21.2", "command (Nix) name", "2.21.2"},
+		{"nix (Lix, like Nix) 2.90.0-beta.1", "nix", "2.90.0-beta.1"},
+	}
+
+	for _, tt := range cases {
+		t.Run(tt.in, func(t *testing.T) {
+			got, err := parseVersionInfo([]byte(tt.in))
+			if err != nil {
+				t.Error("got parse error:", err)
+			}
+			if got.Name != tt.name {
+				t.Errorf("got Name = %q, want %q", got.Name, tt.name)
+			}
+			if got.Version != tt.version {
+				t.Errorf("got Version = %q, want %q", got.Version, tt.version)
+			}
+		})
+	}
 }
 
 func TestParseVersionInfoError(t *testing.T) {