chore(lint): stamp license headers with the current year (#246)

## Summary

### Why?

The license-header linter pinned the copyright year to a hardcoded
`2025` constant and required an exact match, so any file authored in a
later year would need a manual constant bump — and bumping it would
retroactively fail every existing file.

### What?

The header is now validated by pattern: the copyright line matches `//
Copyright (c) <YYYY> Uber Technologies, Inc.` for any 4-digit year,
while the rest of the block must match exactly. The `-fix` mode stamps
`time.Now().Year()`, so new files get the current year automatically
with no future edits. Existing files (all `2025`) keep passing. Added
test cases covering an older year, a wrong company, and a non-numeric
year.

## Test Plan

✅ `bazel test //tool/linter/licenseheader:licenseheader_test`
✅ `bazel run //tool/linter/licenseheader -- -check` (whole repo still
clean)

Author: behinddwalls

tool/linter/licenseheader/main.go

@@ -19,11 +19,16 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
+	"time"
 )
 
-const header = `// Copyright (c) 2025 Uber Technologies, Inc.
-//
+// licenseBody is everything after the copyright line. The copyright line itself
+// carries a year, which is validated by pattern (any 4-digit year) rather than
+// pinned to a single value — so files authored in earlier years keep passing
+// while new files are stamped with the current year.
+const licenseBody = `//
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
@@ -36,6 +41,20 @@ const header = `// Copyright (c) 2025 Uber Technologies, Inc.
 // See the License for the specific language governing permissions and
 // limitations under the License.`
 
+// copyrightLineRe matches the first line of the header with any 4-digit year.
+var copyrightLineRe = regexp.MustCompile(`^// Copyright \(c\) \d{4} Uber Technologies, Inc\.$`)
+
+// copyrightLine returns the copyright line for a given year.
+func copyrightLine(year int) string {
+	return fmt.Sprintf("// Copyright (c) %d Uber Technologies, Inc.", year)
+}
+
+// header returns the full license header stamped with the given year, used when
+// adding a header in -fix mode.
+func header(year int) string {
+	return copyrightLine(year) + "\n" + licenseBody
+}
+
 func main() {
 	fix := flag.Bool("fix", false, "add missing license headers in-place")
 	check := flag.Bool("check", false, "check for missing license headers (default mode)")
@@ -156,6 +175,7 @@ func isGeneratedFile(path string) bool {
 }
 
 // hasLicenseHeader checks if a file starts with the expected license header.
+// The copyright year may be any 4-digit year; the rest must match exactly.
 func hasLicenseHeader(path string) (bool, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
@@ -171,30 +191,40 @@ func hasLicenseHeader(path string) (bool, error) {
 		}
 	}
 
-	return strings.HasPrefix(content, header), nil
+	nl := strings.Index(content, "\n")
+	if nl < 0 {
+		return false, nil
+	}
+	if !copyrightLineRe.MatchString(content[:nl]) {
+		return false, nil
+	}
+	return strings.HasPrefix(content[nl+1:], licenseBody), nil
 }
 
-// addLicenseHeader prepends the license header to a file.
-// If the file starts with a //go:build directive, the header is placed after it.
+// addLicenseHeader prepends the license header (stamped with the current year)
+// to a file. If the file starts with a //go:build directive, the header is
+// placed after it.
 func addLicenseHeader(path string) error {
 	data, err := os.ReadFile(path)
 	if err != nil {
 		return err
 	}
 	content := string(data)
 
+	hdr := header(time.Now().Year())
+
 	var result string
 	if strings.HasPrefix(content, "//go:build ") {
 		idx := strings.Index(content, "\n")
 		if idx >= 0 {
 			buildLine := content[:idx+1]
 			rest := content[idx+1:]
-			result = buildLine + "\n" + header + "\n\n" + strings.TrimLeft(rest, "\n")
+			result = buildLine + "\n" + hdr + "\n\n" + strings.TrimLeft(rest, "\n")
 		} else {
-			result = content + "\n\n" + header + "\n"
+			result = content + "\n\n" + hdr + "\n"
 		}
 	} else {
-		result = header + "\n\n" + content
+		result = hdr + "\n\n" + content
 	}
 
 	return os.WriteFile(path, []byte(result), 0644)

tool/linter/licenseheader/main_test.go

@@ -19,6 +19,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -46,14 +47,21 @@ func TestIsGeneratedFile(t *testing.T) {
 func TestHasLicenseHeader(t *testing.T) {
 	dir := t.TempDir()
 
+	curr := header(time.Now().Year())
+
 	tests := []struct {
 		name    string
 		content string
 		want    bool
 	}{
 		{
 			name:    "has header",
-			content: header + "\n\npackage foo\n",
+			content: curr + "\n\npackage foo\n",
+			want:    true,
+		},
+		{
+			name:    "older year still valid",
+			content: header(2025) + "\n\npackage foo\n",
 			want:    true,
 		},
 		{
@@ -63,14 +71,24 @@ func TestHasLicenseHeader(t *testing.T) {
 		},
 		{
 			name:    "go:build then header",
-			content: "//go:build linux\n\n" + header + "\n\npackage foo\n",
+			content: "//go:build linux\n\n" + curr + "\n\npackage foo\n",
 			want:    true,
 		},
 		{
 			name:    "go:build without header",
 			content: "//go:build linux\n\npackage foo\n",
 			want:    false,
 		},
+		{
+			name:    "wrong company fails",
+			content: "// Copyright (c) 2025 Someone Else, Inc.\n" + licenseBody + "\n\npackage foo\n",
+			want:    false,
+		},
+		{
+			name:    "non-numeric year fails",
+			content: "// Copyright (c) YYYY Uber Technologies, Inc.\n" + licenseBody + "\n\npackage foo\n",
+			want:    false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -96,7 +114,7 @@ func TestAddLicenseHeader(t *testing.T) {
 		require.NoError(t, err)
 		content := string(data)
 
-		assert.True(t, strings.HasPrefix(content, header))
+		assert.True(t, strings.HasPrefix(content, header(time.Now().Year())))
 		assert.Contains(t, content, "package foo")
 	})
 
@@ -112,7 +130,7 @@ func TestAddLicenseHeader(t *testing.T) {
 		content := string(data)
 
 		assert.True(t, strings.HasPrefix(content, "//go:build linux\n"))
-		assert.Contains(t, content, header)
+		assert.Contains(t, content, header(time.Now().Year()))
 		assert.Contains(t, content, "package foo")
 
 		// Verify order: build directive, then header, then package
@@ -158,7 +176,7 @@ func TestAddLicenseHeader(t *testing.T) {
 		require.NoError(t, err)
 		content := string(data)
 
-		assert.True(t, strings.HasPrefix(content, header))
+		assert.True(t, strings.HasPrefix(content, header(time.Now().Year())))
 		assert.Contains(t, content, "syntax = \"proto3\"")
 	})
 }