Use unique versions in staggered versioner (fixes #1063)

internal/versioner/simple.go

@@ -18,7 +18,6 @@ package versioner
 import (
 	"os"
 	"path/filepath"
-	"sort"
 	"strconv"
 
 	"github.com/syncthing/syncthing/internal/osutil"
@@ -124,10 +123,9 @@ func (v Simple) Archive(filePath string) error {
 
 	// Use all the found filenames. "~" sorts after "." so all old pattern
 	// files will be deleted before any new, which is as it should be.
-	versions := append(oldVersions, newVersions...)
+	versions := uniqueSortedStrings(append(oldVersions, newVersions...))
 
 	if len(versions) > v.keep {
-		sort.Strings(versions)
 		for _, toRemove := range versions[:len(versions)-v.keep] {
 			if debug {
 				l.Debugln("cleaning out", toRemove)

internal/versioner/staggered.go

@@ -18,7 +18,6 @@ package versioner
 import (
 	"os"
 	"path/filepath"
-	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -357,9 +356,7 @@ func (v Staggered) Archive(filePath string) error {
 
 	// Use all the found filenames.
 	versions := append(oldVersions, newVersions...)
-
+	v.expire(uniqueSortedStrings(versions))
-	sort.Strings(versions)
-	v.expire(versions)
 
 	return nil
 }

internal/versioner/util.go

@@ -18,6 +18,7 @@ package versioner
 import (
 	"path/filepath"
 	"regexp"
+	"sort"
 )
 
 // Inserts ~tag just before the extension of the filename.
@@ -40,3 +41,17 @@ func filenameTag(path string) string {
 	}
 	return match[1]
 }
+
+func uniqueSortedStrings(strings []string) []string {
+	seen := make(map[string]struct{}, len(strings))
+	unique := make([]string, 0, len(strings))
+	for _, str := range strings {
+		_, ok := seen[str]
+		if !ok {
+			seen[str] = struct{}{}
+			unique = append(unique, str)
+		}
+	}
+	sort.Strings(unique)
+	return unique
+}