feat(build): stamp commit, build number, and date into the binary

Makefile

@@ -4,8 +4,13 @@
 BINARY_NAME=late
 VERSION?=2.0.0-rc.1
 
-# Go compiler flags
-LDFLAGS=-ldflags "-X late/internal/common.Version=${VERSION}"
+# Go compiler flags. Commit/build-number/build-date stamping: when git is
+# unavailable (tarball checkout, no repo) the commit and build number
+# degrade to "unknown" without failing the build.
+GIT_COMMIT:=$(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
+BUILD_NUMBER:=$(shell git rev-list --count HEAD 2>/dev/null || echo unknown)
+BUILD_DATE:=$(shell date -u +%Y-%m-%dT%H:%M:%SZ)
+LDFLAGS=-ldflags "-X late/internal/common.Version=${VERSION} -X late/internal/common.BuildNumber=${BUILD_NUMBER} -X late/internal/common.Commit=${GIT_COMMIT} -X 'late/internal/common.BuildDate=${BUILD_DATE}'"
 
 help: ## Show this help
 	@awk 'BEGIN {FS = ":.*?## "} /^[a-zA-Z_-]+:.*?## / {printf "\033[36m%-15s\033[0m %s\n", $$1, $$2}' $(MAKEFILE_LIST)

cmd/late/main.go

@@ -128,7 +128,9 @@ func main() {
 	tool.SetSqzEnabled(*enableSqzReq)
 
 	if *versionReq {
-		fmt.Printf("late %s\n", common.Version)
+		// Full one-line build identity: version + stamped commit/build
+		// date, degrading to the bare dev banner for a plain `go build`.
+		fmt.Println(common.VersionDisplay())
 		return
 	}
 

internal/common/version.go

@@ -1,3 +1,93 @@
 package common
 
+import "strings"
+
+// Version is the release identifier (e.g. "2.0.0-rc.1"), set via
+// -ldflags -X at build time; it stays "dev" for a plain `go build`.
 var Version = "dev"
+
+// BuildNumber is the deterministic build ordinal — the commit count of the
+// current HEAD (`git rev-list --count HEAD`), set via -ldflags -X at build
+// time (Makefile: BUILD_NUMBER). It is stable for the same commit, grows
+// monotonically as the repo grows, and needs no network; it stays "unknown"
+// when not stamped (plain `go build`) or when git is unavailable (tarball
+// without .git).
+var BuildNumber = "unknown"
+
+// Commit is the short git commit the binary was built from, set via
+// -ldflags -X at build time (Makefile: `git rev-parse --short HEAD`);
+// it stays "unknown" when not stamped (plain `go build`, tarball
+// without .git).
+var Commit = "unknown"
+
+// BuildDate is the UTC build timestamp (RFC3339), set via -ldflags -X
+// at build time (Makefile: `date -u +%Y-%m-%dT%H:%M:%SZ`); it stays
+// "unknown" when not stamped.
+var BuildDate = "unknown"
+
+// versionDisplay renders the one-line build identity from injected
+// values, so tests can exercise every degradation without mutating the
+// package vars:
+//
+//	late 2.0.0-rc.1 (build 1239, commit 2fe0e83, built 2026-09-25T13:12:11Z)
+//
+// Degradations (the output stays on one line):
+//   - unknown build number ("unknown" or empty) → the build number is omitted;
+//   - unknown commit ("unknown" or empty) → the commit is omitted;
+//   - unknown date ("unknown" or empty) → the date is omitted;
+//   - dev version with nothing stamped (plain `go build`) → bare "late dev".
+func versionDisplay(version, buildNumber, commit, buildDate string) string {
+	buildKnown := buildNumber != "" && buildNumber != "unknown"
+	commitKnown := commit != "" && commit != "unknown"
+	dateKnown := buildDate != "" && buildDate != "unknown"
+	if version == "dev" && !buildKnown && !commitKnown && !dateKnown {
+		return "late dev"
+	}
+	display := "late " + version
+	var meta []string
+	if buildKnown {
+		meta = append(meta, "build "+buildNumber)
+	}
+	if commitKnown {
+		meta = append(meta, "commit "+commit)
+	}
+	if dateKnown {
+		meta = append(meta, "built "+buildDate)
+	}
+	if len(meta) > 0 {
+		display += " (" + strings.Join(meta, ", ") + ")"
+	}
+	return display
+}
+
+// VersionDisplay renders the full one-line build identity for -version
+// from the stamped package vars. See versionDisplay for the format and
+// its graceful degradations.
+func VersionDisplay() string {
+	return versionDisplay(Version, BuildNumber, Commit, BuildDate)
+}
+
+// versionDisplayShort renders the compact identity used where only one
+// row must fit (the TUI info bar): "<version>[ · b<build number>][ ·
+// <commit>]" — the build number comes first, then the short commit. Each
+// unknown piece degrades silently to just the version, and the build date
+// is deliberately left out.
+func versionDisplayShort(version, buildNumber, commit string) string {
+	parts := make([]string, 0, 3)
+	if version != "" {
+		parts = append(parts, version)
+	}
+	if buildNumber != "" && buildNumber != "unknown" {
+		parts = append(parts, "b"+buildNumber)
+	}
+	if commit != "" && commit != "unknown" {
+		parts = append(parts, commit)
+	}
+	return strings.Join(parts, " · ")
+}
+
+// VersionDisplayShort renders the short build identity from the stamped
+// package vars. See versionDisplayShort for the format.
+func VersionDisplayShort() string {
+	return versionDisplayShort(Version, BuildNumber, Commit)
+}

internal/common/version_test.go

@@ -0,0 +1,211 @@
+package common
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestVersionDisplay(t *testing.T) {
+	tests := []struct {
+		name      string
+		version   string
+		buildNum  string
+		commit    string
+		buildDate string
+		want      string
+	}{
+		{
+			name:      "all four pieces stamped, order is build, commit, built",
+			version:   "2.0.0-rc.1",
+			buildNum:  "1239",
+			commit:    "2fe0e83",
+			buildDate: "2026-09-25T13:12:11Z",
+			want:      "late 2.0.0-rc.1 (build 1239, commit 2fe0e83, built 2026-09-25T13:12:11Z)",
+		},
+		{
+			name:     "build number only",
+			version:  "2.0.0-rc.1",
+			buildNum: "1239",
+			want:     "late 2.0.0-rc.1 (build 1239)",
+		},
+		{
+			name:      "build number and build date omit the commit",
+			version:   "2.0.0-rc.1",
+			buildNum:  "1239",
+			buildDate: "2026-09-25T13:12:11Z",
+			want:      "late 2.0.0-rc.1 (build 1239, built 2026-09-25T13:12:11Z)",
+		},
+		{
+			name:      "commit and build date stamped without build number",
+			version:   "2.0.0-rc.1",
+			commit:    "2fe0e83",
+			buildDate: "2026-09-25T10:57:00+02:00",
+			want:      "late 2.0.0-rc.1 (commit 2fe0e83, built 2026-09-25T10:57:00+02:00)",
+		},
+		{
+			name:    "commit only",
+			version: "2.0.0-rc.1",
+			commit:  "2fe0e83",
+			want:    "late 2.0.0-rc.1 (commit 2fe0e83)",
+		},
+		{
+			name:      "build date only",
+			version:   "2.0.0-rc.1",
+			buildDate: "2026-09-25T08:57:00Z",
+			want:      "late 2.0.0-rc.1 (built 2026-09-25T08:57:00Z)",
+		},
+		{
+			name:    "nothing stamped",
+			version: "2.0.0-rc.1",
+			want:    "late 2.0.0-rc.1",
+		},
+		{
+			name:    "dev with nothing stamped is the bare dev banner",
+			version: "dev",
+			want:    "late dev",
+		},
+		{
+			name:      "unknown sentinels are treated as unstamped",
+			version:   "2.0.0-rc.1",
+			buildNum:  "unknown",
+			commit:    "unknown",
+			buildDate: "unknown",
+			want:      "late 2.0.0-rc.1",
+		},
+		{
+			name:     "empty build number is treated as unstamped",
+			version:  "2.0.0-rc.1",
+			buildNum: "",
+			commit:   "2fe0e83",
+			want:     "late 2.0.0-rc.1 (commit 2fe0e83)",
+		},
+		{
+			name:     "dev with only the build number stamped keeps it",
+			version:  "dev",
+			buildNum: "1239",
+			want:     "late dev (build 1239)",
+		},
+		{
+			name:      "dev with only the build date stamped keeps the date",
+			version:   "dev",
+			buildDate: "2026-09-25T08:57:00Z",
+			want:      "late dev (built 2026-09-25T08:57:00Z)",
+		},
+		{
+			name:    "dev with only the commit stamped keeps the commit",
+			version: "dev",
+			commit:  "2fe0e83",
+			want:    "late dev (commit 2fe0e83)",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := versionDisplay(tt.version, tt.buildNum, tt.commit, tt.buildDate)
+			if got != tt.want {
+				t.Errorf("versionDisplay(%q, %q, %q, %q) = %q, want %q", tt.version, tt.buildNum, tt.commit, tt.buildDate, got, tt.want)
+			}
+			// The output must stay on one line: it feeds -version stdout
+			// and single-row parsers.
+			if strings.ContainsAny(got, "\n\r") {
+				t.Errorf("versionDisplay(...) = %q, must not contain line breaks", got)
+			}
+		})
+	}
+}
+
+func TestVersionDisplayShort(t *testing.T) {
+	tests := []struct {
+		name     string
+		version  string
+		buildNum string
+		commit   string
+		want     string
+	}{
+		{
+			name:     "build number precedes the commit",
+			version:  "2.0.0-rc.1",
+			buildNum: "1239",
+			commit:   "2fe0e83",
+			want:     "2.0.0-rc.1 · b1239 · 2fe0e83",
+		},
+		{
+			name:     "build number only",
+			version:  "2.0.0-rc.1",
+			buildNum: "1239",
+			want:     "2.0.0-rc.1 · b1239",
+		},
+		{
+			name:    "commit only",
+			version: "2.0.0-rc.1",
+			commit:  "2fe0e83",
+			want:    "2.0.0-rc.1 · 2fe0e83",
+		},
+		{
+			name:     "unknown build number degrades to version and commit",
+			version:  "2.0.0-rc.1",
+			buildNum: "unknown",
+			commit:   "2fe0e83",
+			want:     "2.0.0-rc.1 · 2fe0e83",
+		},
+		{
+			name:     "empty build number degrades to version and commit",
+			version:  "2.0.0-rc.1",
+			buildNum: "",
+			commit:   "2fe0e83",
+			want:     "2.0.0-rc.1 · 2fe0e83",
+		},
+		{
+			name:    "unknown commit degrades to the bare version",
+			version: "2.0.0-rc.1",
+			commit:  "unknown",
+			want:    "2.0.0-rc.1",
+		},
+		{
+			name:    "empty commit degrades to the bare version",
+			version: "2.0.0-rc.1",
+			want:    "2.0.0-rc.1",
+		},
+		{
+			name:    "dev with unknown commit",
+			version: "dev",
+			want:    "dev",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := versionDisplayShort(tt.version, tt.buildNum, tt.commit)
+			if got != tt.want {
+				t.Errorf("versionDisplayShort(%q, %q, %q) = %q, want %q", tt.version, tt.buildNum, tt.commit, got, tt.want)
+			}
+			if strings.ContainsAny(got, "\n\r") {
+				t.Errorf("versionDisplayShort(...) = %q, must not contain line breaks", got)
+			}
+		})
+	}
+}
+
+// TestVersionDisplayWrappersUseVars pins that the thin var-backed wrappers
+// plumb the package vars through (the build-tag-free injection point used
+// by the TUI tests).
+func TestVersionDisplayWrappersUseVars(t *testing.T) {
+	origVersion, origBuildNum, origCommit, origBuildDate := Version, BuildNumber, Commit, BuildDate
+	defer func() { Version, BuildNumber, Commit, BuildDate = origVersion, origBuildNum, origCommit, origBuildDate }()
+
+	Version, BuildNumber, Commit, BuildDate = "2.0.0-rc.1", "1239", "2fe0e83", "2026-09-25T10:57:00+02:00"
+	if got, want := VersionDisplay(), "late 2.0.0-rc.1 (build 1239, commit 2fe0e83, built 2026-09-25T10:57:00+02:00)"; got != want {
+		t.Errorf("VersionDisplay() = %q, want %q", got, want)
+	}
+	if got, want := VersionDisplayShort(), "2.0.0-rc.1 · b1239 · 2fe0e83"; got != want {
+		t.Errorf("VersionDisplayShort() = %q, want %q", got, want)
+	}
+
+	// A plain `go build` (all vars at their source defaults) is the bare
+	// dev banner.
+	Version, BuildNumber, Commit, BuildDate = "dev", "unknown", "unknown", "unknown"
+	if got := VersionDisplay(); got != "late dev" {
+		t.Errorf("VersionDisplay() = %q, want %q", got, "late dev")
+	}
+	if got := VersionDisplayShort(); got != "dev" {
+		t.Errorf("VersionDisplayShort() = %q, want %q", got, "dev")
+	}
+}