fix: self-report version from build info (correct for go install)

The version was only stamped via ldflags (GoReleaser / make), so `go install`
builds reported the hardcoded dev default. Resolve it with precedence
ldflags > embedded module version (go install …@vX.Y.Z) > VCS revision > dev,
via runtime/debug.ReadBuildInfo. Covered by a table test. Document the rule that
published tags must never be moved (the module proxy caches them immutably).

Author: diomonogatari

CONTRIBUTING.md

@@ -62,5 +62,14 @@ goreleaser check                       # validate .goreleaser.yaml
 goreleaser release --snapshot --clean  # full build into ./dist
 ```
 
+> ⚠️ **Never move or re-point a published tag.** The Go module proxy caches every
+> `vX.Y.Z` immutably, so moving a tag silently breaks `go install` even when
+> GitHub shows the new commit. Always bump to a fresh version instead.
+
+The binary's version is resolved automatically (`internal/cli.resolveVersion`):
+ldflags for release / `make` builds, the embedded module version for
+`go install …@vX.Y.Z`, and a `dev-<rev>` string for plain `go build` — so no
+build mode reports a stale version.
+
 CI (`.github/workflows/ci.yml`) runs gofmt, vet, build, and tests on every push
 and pull request.

internal/cli/cli.go

@@ -7,6 +7,7 @@ import (
 	"math"
 	"os"
 	"os/exec"
+	"runtime/debug"
 	"time"
 
 	"github.com/diomonogatari/hydrate-cli/internal/config"
@@ -15,8 +16,49 @@ import (
 	"github.com/diomonogatari/hydrate-cli/internal/store"
 )
 
-// version is overridable at build time with -ldflags "-X ...cli.version=...".
-var version = "0.1.0-dev"
+// version is set at build time via -ldflags "-X ...cli.version=..." by GoReleaser
+// and `make build`. When empty (e.g. a `go install [email protected]` build, which gets
+// no ldflags), resolveVersion falls back to the module/VCS info the Go toolchain
+// embeds — so released binaries always self-report a real version.
+var version = ""
+
+// resolveVersion returns the best available version string for this build.
+func resolveVersion() string {
+	bi, _ := debug.ReadBuildInfo()
+	return versionFrom(version, bi)
+}
+
+// versionFrom is the pure resolution logic, separated for testing. Precedence:
+// ldflags > module version (`go install module@v…`) > VCS revision > "dev".
+func versionFrom(ldflagsVer string, bi *debug.BuildInfo) string {
+	if ldflagsVer != "" {
+		return ldflagsVer
+	}
+	if bi == nil {
+		return "dev"
+	}
+	if v := bi.Main.Version; v != "" && v != "(devel)" {
+		return v
+	}
+	var rev, dirty string
+	for _, s := range bi.Settings {
+		switch s.Key {
+		case "vcs.revision":
+			rev = s.Value
+		case "vcs.modified":
+			if s.Value == "true" {
+				dirty = "-dirty"
+			}
+		}
+	}
+	if rev != "" {
+		if len(rev) > 12 {
+			rev = rev[:12]
+		}
+		return "dev-" + rev + dirty
+	}
+	return "dev"
+}
 
 // Run is the program entry point. It returns a process exit code.
 func Run(args []string) int {
@@ -30,7 +72,7 @@ func Run(args []string) int {
 			usage(os.Stdout)
 			return 0
 		case "version", "-v", "--version":
-			fmt.Println("hydrate", version)
+			fmt.Println("hydrate", resolveVersion())
 			return 0
 		}
 	}

internal/cli/cli_test.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"os"
+	"runtime/debug"
 	"testing"
 )
 
@@ -35,3 +36,34 @@ func TestRunTopLevelDispatch(t *testing.T) {
 		}
 	}
 }
+
+func TestVersionFrom(t *testing.T) {
+	mod := func(v string) *debug.BuildInfo { return &debug.BuildInfo{Main: debug.Module{Version: v}} }
+	withVCS := func(rev, modified string) *debug.BuildInfo {
+		return &debug.BuildInfo{
+			Main: debug.Module{Version: "(devel)"},
+			Settings: []debug.BuildSetting{
+				{Key: "vcs.revision", Value: rev},
+				{Key: "vcs.modified", Value: modified},
+			},
+		}
+	}
+
+	cases := []struct {
+		name    string
+		ldflags string
+		bi      *debug.BuildInfo
+		want    string
+	}{
+		{"ldflags wins", "1.0.2", mod("v9.9.9"), "1.0.2"},
+		{"go install module version", "", mod("v1.0.2"), "v1.0.2"},
+		{"devel falls to vcs (dirty)", "", withVCS("0123456789abcdef0", "true"), "dev-0123456789ab-dirty"},
+		{"devel falls to vcs (clean)", "", withVCS("0123456789abcdef0", "false"), "dev-0123456789ab"},
+		{"no build info", "", nil, "dev"},
+	}
+	for _, c := range cases {
+		if got := versionFrom(c.ldflags, c.bi); got != c.want {
+			t.Errorf("%s: versionFrom(%q, …) = %q, want %q", c.name, c.ldflags, got, c.want)
+		}
+	}
+}