fix(version): use debug.ReadBuildInfo for go-install builds

internal/cli/version.go

@@ -4,15 +4,54 @@ import (
 	"fmt"
 	"io"
 	"runtime"
+	"runtime/debug"
 )
 
-// Set via -ldflags "-X github.com/plinth-dev/cli/internal/cli.Version=..." at build.
+// Set via -ldflags "-X github.com/plinth-dev/cli/internal/cli.Version=..." at
+// build (see Makefile). When unset — e.g. when the user installs via
+// `go install ...@v0.1.0` — runtime/debug.ReadBuildInfo provides the module
+// version and VCS revision Go's toolchain stamped into the binary.
 var (
-	Version = "dev"
-	Commit  = "none"
+	Version = ""
+	Commit  = ""
 )
 
 func runVersion(stdout io.Writer) int {
-	fmt.Fprintf(stdout, "plinth %s (commit %s, %s)\n", Version, Commit, runtime.Version())
+	v, c := resolveVersion(Version, Commit)
+	fmt.Fprintf(stdout, "plinth %s (commit %s, %s)\n", v, c, runtime.Version())
 	return 0
 }
+
+func resolveVersion(version, commit string) (string, string) {
+	if version != "" && commit != "" {
+		return version, commit
+	}
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return fallback(version, "dev"), fallback(commit, "none")
+	}
+	if version == "" {
+		if v := info.Main.Version; v != "" && v != "(devel)" {
+			version = v
+		}
+	}
+	if commit == "" {
+		for _, s := range info.Settings {
+			if s.Key == "vcs.revision" && s.Value != "" {
+				commit = s.Value
+				if len(commit) > 12 {
+					commit = commit[:12]
+				}
+				break
+			}
+		}
+	}
+	return fallback(version, "dev"), fallback(commit, "none")
+}
+
+func fallback(s, def string) string {
+	if s == "" {
+		return def
+	}
+	return s
+}

internal/cli/version_test.go

@@ -23,3 +23,22 @@ func TestVersionPrints(t *testing.T) {
 		t.Errorf("missing commit: %s", got)
 	}
 }
+
+func TestResolveVersionPrefersExplicit(t *testing.T) {
+	v, c := resolveVersion("0.2.0", "deadbeef")
+	if v != "0.2.0" || c != "deadbeef" {
+		t.Errorf("explicit args lost: v=%q c=%q", v, c)
+	}
+}
+
+func TestResolveVersionFallback(t *testing.T) {
+	// In `go test` runs, debug.ReadBuildInfo reports Main.Version="(devel)"
+	// and no vcs.revision setting, so both should land on the dev/none defaults.
+	v, c := resolveVersion("", "")
+	if v != "dev" {
+		t.Errorf("unset version did not fall back to dev: %q", v)
+	}
+	if c == "" {
+		t.Errorf("commit must not be empty after fallback")
+	}
+}