fix(version): report module version for go-install builds

docs/user-guide/version.md

@@ -16,9 +16,9 @@ a6 version v1.2.3
 
 | Field | Source |
 |---|---|
-| `version` | Tagged release if built from a tag (e.g. `v0.1.0-rc1`); otherwise the short commit. `dev` when built without ldflags. |
-| `commit`  | Short Git commit the binary was built from. |
-| `built`   | UTC timestamp of the build. |
+| `version` | Release tag injected at build time (`make build`, GoReleaser), or the Go module version for binaries installed with `go install github.com/api7/a6/cmd/a6@<tag>`. `dev` only for untagged local source builds. |
+| `commit`  | Short Git commit the binary was built from (build-time injection, or VCS info embedded by `go build`). `unknown` when neither is available, e.g. `go install` module builds. |
+| `built`   | UTC timestamp of the build (same sources as `commit`). |
 | `go`      | Go toolchain used. |
 | `platform` | `<GOOS>/<GOARCH>` of the binary. |
 

internal/version/version.go

@@ -1,5 +1,7 @@
 package version
 
+import "runtime/debug"
+
 // These variables are set at build time via ldflags.
 var (
 	// Version is the semantic version (e.g., "v0.1.0").
@@ -9,3 +11,42 @@ var (
 	// Date is the build date in UTC.
 	Date = "unknown"
 )
+
+// init falls back to the Go module build info for any value that was not
+// injected via ldflags, so that binaries installed with
+// `go install github.com/api7/a6/cmd/a6@<tag>` report the module version
+// instead of "dev".
+func init() {
+	if info, ok := debug.ReadBuildInfo(); ok {
+		Version, Commit, Date = resolve(Version, Commit, Date, info)
+	}
+}
+
+// resolve returns version, commit, and date with unset (default) values
+// filled in from build info. Values already set via ldflags take precedence.
+func resolve(version, commit, date string, info *debug.BuildInfo) (string, string, string) {
+	if version == "dev" && info.Main.Version != "" && info.Main.Version != "(devel)" {
+		version = info.Main.Version
+	}
+
+	var revision, vcsTime string
+	for _, s := range info.Settings {
+		switch s.Key {
+		case "vcs.revision":
+			revision = s.Value
+		case "vcs.time":
+			vcsTime = s.Value
+		}
+	}
+	if commit == "unknown" && revision != "" {
+		if len(revision) > 7 {
+			revision = revision[:7]
+		}
+		commit = revision
+	}
+	if date == "unknown" && vcsTime != "" {
+		date = vcsTime
+	}
+
+	return version, commit, date
+}

internal/version/version_test.go

@@ -0,0 +1,68 @@
+package version
+
+import (
+	"runtime/debug"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestResolve_GoInstallModuleVersion(t *testing.T) {
+	// `go install .../cmd/a6@v1.0.0` embeds the module version but no ldflags.
+	info := &debug.BuildInfo{Main: debug.Module{Version: "v1.0.0"}}
+
+	v, c, d := resolve("dev", "unknown", "unknown", info)
+
+	assert.Equal(t, "v1.0.0", v)
+	assert.Equal(t, "unknown", c)
+	assert.Equal(t, "unknown", d)
+}
+
+func TestResolve_DevelBuildStaysDev(t *testing.T) {
+	// `go build` from a source checkout reports "(devel)" as the module version.
+	info := &debug.BuildInfo{Main: debug.Module{Version: "(devel)"}}
+
+	v, _, _ := resolve("dev", "unknown", "unknown", info)
+
+	assert.Equal(t, "dev", v)
+}
+
+func TestResolve_LdflagsTakePrecedence(t *testing.T) {
+	info := &debug.BuildInfo{
+		Main: debug.Module{Version: "v9.9.9"},
+		Settings: []debug.BuildSetting{
+			{Key: "vcs.revision", Value: "ffffffffffffffffffffffffffffffffffffffff"},
+			{Key: "vcs.time", Value: "2026-01-01T00:00:00Z"},
+		},
+	}
+
+	v, c, d := resolve("v1.2.3", "abc1234", "2026-05-27T03:23:51Z", info)
+
+	assert.Equal(t, "v1.2.3", v)
+	assert.Equal(t, "abc1234", c)
+	assert.Equal(t, "2026-05-27T03:23:51Z", d)
+}
+
+func TestResolve_VCSSettingsFallback(t *testing.T) {
+	info := &debug.BuildInfo{
+		Main: debug.Module{Version: "(devel)"},
+		Settings: []debug.BuildSetting{
+			{Key: "vcs.revision", Value: "0123456789abcdef0123456789abcdef01234567"},
+			{Key: "vcs.time", Value: "2026-06-03T00:00:00Z"},
+		},
+	}
+
+	v, c, d := resolve("dev", "unknown", "unknown", info)
+
+	assert.Equal(t, "dev", v)
+	assert.Equal(t, "0123456", c, "commit should be shortened to 7 characters")
+	assert.Equal(t, "2026-06-03T00:00:00Z", d)
+}
+
+func TestResolve_EmptyBuildInfo(t *testing.T) {
+	v, c, d := resolve("dev", "unknown", "unknown", &debug.BuildInfo{})
+
+	assert.Equal(t, "dev", v)
+	assert.Equal(t, "unknown", c)
+	assert.Equal(t, "unknown", d)
+}