cmd: add a 'version' subcommand and flag to show the version

cmd/main.go

@@ -5,6 +5,8 @@ import (
 	"os"
 
 	"github.com/spf13/cobra"
+
+	"git.offline-twitter.com/offline-labs/gas-stack/pkg/version"
 )
 
 const (
@@ -16,12 +18,16 @@ const (
 func main() {
 	root_cmd := &cobra.Command{
 		Use:           "gas",
+		Version:       version.String(),
 		SilenceErrors: true,
 		SilenceUsage:  true,
 	}
+	// Print a bare version string ("v0.0.4"), rather than cobra's "gas version v0.0.4".
+	root_cmd.SetVersionTemplate("{{.Version}}\n")
 	root_cmd.AddCommand(sqlite_lint)
 	root_cmd.AddCommand(cmd_init)
 	root_cmd.AddCommand(generate_model)
+	root_cmd.AddCommand(cmd_version)
 	if err := root_cmd.Execute(); err != nil {
 		fmt.Println(RED + err.Error() + RESET)
 		os.Exit(1)

cmd/subcmd_version.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+
+	"git.offline-twitter.com/offline-labs/gas-stack/pkg/version"
+)
+
+var cmd_version = &cobra.Command{
+	Use:   "version",
+	Short: "Print the version of `gas`",
+	Args:  cobra.NoArgs,
+
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Println(version.String())
+	},
+}

ops/compile.sh

@@ -1,3 +1,10 @@
 #!/bin/sh
 
-go build -tags fts5 -o gas ./cmd
+# Stamp the version into the binary.  `git describe` fails when this isn't a git checkout (e.g. a
+# source export with no .git dir); in that case leave it empty, and pkg/version falls back to the
+# build info that the Go toolchain embeds.
+VERSION=$(git describe --tags --always --dirty 2>/dev/null)
+
+go build -tags fts5 \
+    -ldflags "-X git.offline-twitter.com/offline-labs/gas-stack/pkg/version.Version=$VERSION" \
+    -o gas ./cmd

pkg/version/version.go

@@ -0,0 +1,55 @@
+package version
+
+import (
+	"fmt"
+	"runtime/debug"
+)
+
+// Version is stamped in at compile time by `ops/compile.sh`, via:
+//
+//	-ldflags "-X git.offline-twitter.com/offline-labs/gas-stack/pkg/version.Version=v0.0.4"
+//
+// It's empty for builds that don't go through that script-- most importantly
+// `go install git.offline-twitter.com/offline-labs/gas-stack/cmd@v0.0.4`, which is the normal way
+// to install `gas`.  In that case, String() recovers the version from the build info that the Go
+// toolchain embeds in every binary.
+var Version = ""
+
+// String returns the version of this binary, e.g. "v0.0.4".
+func String() string {
+	if Version != "" {
+		return Version
+	}
+
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return "unknown"
+	}
+
+	// Set by `go install module@version`, and (as of Go 1.24) by `go build` in a git checkout
+	// that has the tags available.  It's "(devel)" if the toolchain couldn't work out a version.
+	if info.Main.Version != "" && info.Main.Version != "(devel)" {
+		return info.Main.Version
+	}
+
+	// No module version, so fall back to the commit.  This happens when building from a source
+	// tree with no usable VCS metadata: a git worktree, a `.git`-less export, or `-buildvcs=false`.
+	var revision, dirty string
+	for _, setting := range info.Settings {
+		switch setting.Key {
+		case "vcs.revision":
+			revision = setting.Value
+		case "vcs.modified":
+			if setting.Value == "true" {
+				dirty = "-dirty"
+			}
+		}
+	}
+	if revision == "" {
+		return "unknown"
+	}
+	if len(revision) > 12 {
+		revision = revision[:12]
+	}
+	return fmt.Sprintf("devel-%s%s", revision, dirty)
+}