util/codegen, all: use latest year, not time.Now, in generated files

Updates #6865

Change-Id: I6b86c646968ebbd4553cf37df5e5612fbf5c5f7d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

1 files changed, 59 insertions, 5 deletions

diff --git a/util/codegen/codegen.go b/util/codegen/codegen.go
index 61ec85de8..0e851a7ea 100644
--- a/util/codegen/codegen.go
+++ b/util/codegen/codegen.go
@@ -6,6 +6,7 @@
 package codegen
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
 	"go/ast"
@@ -13,13 +14,16 @@ import (
 	"go/types"
 	"io"
 	"os"
+	"path/filepath"
 	"reflect"
+	"regexp"
+	"strconv"
 	"strings"
-	"time"
 
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/imports"
 	"tailscale.com/util/mak"
+	"tailscale.com/util/must"
 )
 
 // LoadTypes returns all named types in pkgName, keyed by their type name.
@@ -104,15 +108,15 @@ func (it *ImportTracker) Write(w io.Writer) {
 	fmt.Fprintf(w, ")\n\n")
 }
 
-func writeHeader(w io.Writer, tool, pkg string) {
-	fmt.Fprintf(w, header, time.Now().Year(), tool, pkg)
+func writeHeader(w io.Writer, tool, pkg string, copyrightYear int) {
+	fmt.Fprintf(w, header, copyrightYear, tool, pkg)
 }
 
 // WritePackageFile adds a file with the provided imports and contents to package.
 // The tool param is used to identify the tool that generated package file.
-func WritePackageFile(tool string, pkg *packages.Package, path string, it *ImportTracker, contents *bytes.Buffer) error {
+func WritePackageFile(tool string, pkg *packages.Package, path string, copyrightYear int, it *ImportTracker, contents *bytes.Buffer) error {
 	buf := new(bytes.Buffer)
-	writeHeader(buf, tool, pkg.Name)
+	writeHeader(buf, tool, pkg.Name, copyrightYear)
 	it.Write(buf)
 	if _, err := buf.Write(contents.Bytes()); err != nil {
 		return err
@@ -263,3 +267,53 @@ func IsViewType(typ types.Type) bool {
 	}
 	return t.Field(0).Name() == "ж"
 }
+
+// CopyrightYear reports the greatest copyright year in non-generated *.go files
+// in the current directory, for use in the copyright line of generated code.
+//
+// It panics on I/O error, as it's assumed this is only being used by "go
+// generate" or GitHub actions.
+//
+// TODO(bradfitz,dgentry): determine what heuristic to use for all this: latest
+// year, earliest, none? don't list years at all? IANAL. Get advice of others.
+// For now we just want to unbreak the tree. See Issue 6865.
+func CopyrightYear(dir string) (year int) {
+	files, err := os.ReadDir(dir)
+	if err != nil {
+		panic(err)
+	}
+	rxYear := regexp.MustCompile(`^// Copyright \(c\) (20\d{2}) `)
+	rxGenerated := regexp.MustCompile(`^// Code generated .* DO NOT EDIT\.$`)
+Files:
+	for _, f := range files {
+		name := f.Name()
+		if f.IsDir() ||
+			!strings.HasSuffix(name, ".go") ||
+			strings.HasSuffix(name, "_clone.go") ||
+			strings.HasSuffix(name, "_view.go") ||
+			strings.HasSuffix(name, "_test.go") {
+			continue
+		}
+		src, err := os.ReadFile(filepath.Join(dir, name))
+		if err != nil {
+			panic(err)
+		}
+		bs := bufio.NewScanner(bytes.NewReader(src))
+		for bs.Scan() {
+			line := bs.Bytes()
+			if m := rxYear.FindSubmatch(line); m != nil {
+				if y := must.Get(strconv.Atoi(string(m[1]))); y > year {
+					year = y
+				}
+				continue
+			}
+			if rxGenerated.Match(line) {
+				continue Files
+			}
+		}
+	}
+	if year == 0 {
+		panic("no Copyright line found in any *.go file in " + dir)
+	}
+	return year
+}