fix: handle zero time values in LastUpdated sorting functions (#3580)

When GetRepoLastUpdated fails (e.g., redis: nil), it returns time.Time{}
which gets converted to &time.Time{} (not nil). The existing nil checks
in sorting functions didn't account for zero time values, which should
also be treated as "oldest" (sorted last in descending order).

This commit:
- Adds zero time checks in addition to existing nil checks
- Treats both nil and zero time values as "oldest"
- Adds comprehensive tests for zero time edge cases

Affects ImgSortByUpdateTime, RepoSortByUpdateTime, and GetExpandedRepoInfo
sort functions.

Signed-off-by: Andrei Aaron <andreifdaaron@gmail.com>

pkg/extensions/search/pagination/image_pagination.go

@@ -163,17 +163,20 @@ func ImgSortByRelevance(a, b *gql_gen.ImageSummary) int { //nolint:varnamelen //
 
 // ImgSortByUpdateTime sorts descending by image update time.
 func ImgSortByUpdateTime(a, b *gql_gen.ImageSummary) int { //nolint:varnamelen // standard comparison func signature
-	// Handle nil cases: nil values are treated as oldest (come last in descending sort)
-	if a.LastUpdated == nil && b.LastUpdated == nil {
+	// Handle nil and zero time cases: both are treated as oldest (come last in descending sort)
+	aIsZero := a.LastUpdated == nil || (a.LastUpdated != nil && a.LastUpdated.IsZero())
+	bIsZero := b.LastUpdated == nil || (b.LastUpdated != nil && b.LastUpdated.IsZero())
+
+	if aIsZero && bIsZero {
 		return 0
 	}
 
-	if a.LastUpdated == nil {
-		return 1 // a is nil, b is not - a comes after b
+	if aIsZero {
+		return 1 // a is zero/nil, b is not - a comes after b
 	}
 
-	if b.LastUpdated == nil {
-		return -1 // b is nil, a is not - a comes before b
+	if bIsZero {
+		return -1 // b is zero/nil, a is not - a comes before b
 	}
 
 	if a.LastUpdated.After(*b.LastUpdated) {

pkg/extensions/search/pagination/pagination_test.go

@@ -49,25 +49,46 @@ func TestImgSumPagination(t *testing.T) {
 			So(pagination.ImgSortByRelevance(image1, image2), ShouldEqual, -1)
 		})
 
-		Convey("ImgSortByUpdateTime with nil LastUpdated", func() {
+		Convey("ImgSortByUpdateTime with nil and zero LastUpdated", func() {
 			time1 := time.Date(2020, 1, 1, 1, 1, 1, 1, time.UTC)
 			time2 := time.Date(2010, 1, 1, 1, 1, 1, 1, time.UTC)
+			zeroTime := time.Time{}
 
 			// Both nil - should be equal
 			image1 := &gql_generated.ImageSummary{RepoName: ref("repo1"), Tag: ref("tag1"), LastUpdated: nil}
 			image2 := &gql_generated.ImageSummary{RepoName: ref("repo2"), Tag: ref("tag2"), LastUpdated: nil}
 			So(pagination.ImgSortByUpdateTime(image1, image2), ShouldEqual, 0)
 
+			// Both zero time - should be equal (treated same as nil)
+			image1.LastUpdated = &zeroTime
+			image2.LastUpdated = &zeroTime
+			So(pagination.ImgSortByUpdateTime(image1, image2), ShouldEqual, 0)
+
+			// a is nil, b is zero - should be equal (both treated as oldest)
+			image1.LastUpdated = nil
+			image2.LastUpdated = &zeroTime
+			So(pagination.ImgSortByUpdateTime(image1, image2), ShouldEqual, 0)
+
 			// a is nil, b is not - a should come after b (return 1)
 			image1.LastUpdated = nil
 			image2.LastUpdated = &time1
 			So(pagination.ImgSortByUpdateTime(image1, image2), ShouldEqual, 1)
 
+			// a is zero, b is not - a should come after b (return 1)
+			image1.LastUpdated = &zeroTime
+			image2.LastUpdated = &time1
+			So(pagination.ImgSortByUpdateTime(image1, image2), ShouldEqual, 1)
+
 			// b is nil, a is not - a should come before b (return -1)
 			image1.LastUpdated = &time1
 			image2.LastUpdated = nil
 			So(pagination.ImgSortByUpdateTime(image1, image2), ShouldEqual, -1)
 
+			// b is zero, a is not - a should come before b (return -1)
+			image1.LastUpdated = &time1
+			image2.LastUpdated = &zeroTime
+			So(pagination.ImgSortByUpdateTime(image1, image2), ShouldEqual, -1)
+
 			// Both non-nil - normal comparison (a is newer, should come first in descending sort)
 			image1.LastUpdated = &time1
 			image2.LastUpdated = &time2
@@ -393,25 +414,46 @@ func TestPagination(t *testing.T) {
 				So(pagination.RepoSortByDownloads(repo1, repo1), ShouldEqual, 0)
 			})
 
-			Convey("RepoSortByUpdateTime with nil LastUpdated", func() {
+			Convey("RepoSortByUpdateTime with nil and zero LastUpdated", func() {
 				time1 := time.Date(2020, 1, 1, 1, 1, 1, 1, time.UTC)
 				time2 := time.Date(2010, 1, 1, 1, 1, 1, 1, time.UTC)
+				zeroTime := time.Time{}
 
 				// Both nil - should be equal
 				repo1 := &gql_generated.RepoSummary{Name: ref("repo1"), LastUpdated: nil}
 				repo2 := &gql_generated.RepoSummary{Name: ref("repo2"), LastUpdated: nil}
 				So(pagination.RepoSortByUpdateTime(repo1, repo2), ShouldEqual, 0)
 
+				// Both zero time - should be equal (treated same as nil)
+				repo1.LastUpdated = &zeroTime
+				repo2.LastUpdated = &zeroTime
+				So(pagination.RepoSortByUpdateTime(repo1, repo2), ShouldEqual, 0)
+
+				// a is nil, b is zero - should be equal (both treated as oldest)
+				repo1.LastUpdated = nil
+				repo2.LastUpdated = &zeroTime
+				So(pagination.RepoSortByUpdateTime(repo1, repo2), ShouldEqual, 0)
+
 				// a is nil, b is not - a should come after b (return 1)
 				repo1.LastUpdated = nil
 				repo2.LastUpdated = &time1
 				So(pagination.RepoSortByUpdateTime(repo1, repo2), ShouldEqual, 1)
 
+				// a is zero, b is not - a should come after b (return 1)
+				repo1.LastUpdated = &zeroTime
+				repo2.LastUpdated = &time1
+				So(pagination.RepoSortByUpdateTime(repo1, repo2), ShouldEqual, 1)
+
 				// b is nil, a is not - a should come before b (return -1)
 				repo1.LastUpdated = &time1
 				repo2.LastUpdated = nil
 				So(pagination.RepoSortByUpdateTime(repo1, repo2), ShouldEqual, -1)
 
+				// b is zero, a is not - a should come before b (return -1)
+				repo1.LastUpdated = &time1
+				repo2.LastUpdated = &zeroTime
+				So(pagination.RepoSortByUpdateTime(repo1, repo2), ShouldEqual, -1)
+
 				// Both non-nil - normal comparison (a is newer, should come first in descending sort)
 				repo1.LastUpdated = &time1
 				repo2.LastUpdated = &time2

pkg/extensions/search/pagination/repo_pagination.go

@@ -152,17 +152,20 @@ func RepoSortByRelevance(a, b *gql_gen.RepoSummary) int {
 
 // RepoSortByUpdateTime sorts descending by time.
 func RepoSortByUpdateTime(a, b *gql_gen.RepoSummary) int { //nolint:varnamelen // standard comparison func signature
-	// Handle nil cases: nil values are treated as oldest (come last in descending sort)
-	if a.LastUpdated == nil && b.LastUpdated == nil {
+	// Handle nil and zero time cases: both are treated as oldest (come last in descending sort)
+	aIsZero := a.LastUpdated == nil || (a.LastUpdated != nil && a.LastUpdated.IsZero())
+	bIsZero := b.LastUpdated == nil || (b.LastUpdated != nil && b.LastUpdated.IsZero())
+
+	if aIsZero && bIsZero {
 		return 0
 	}
 
-	if a.LastUpdated == nil {
-		return 1 // a is nil, b is not - a comes after b
+	if aIsZero {
+		return 1 // a is zero/nil, b is not - a comes after b
 	}
 
-	if b.LastUpdated == nil {
-		return -1 // b is nil, a is not - a comes before b
+	if bIsZero {
+		return -1 // b is zero/nil, a is not - a comes before b
 	}
 
 	if a.LastUpdated.After(*b.LastUpdated) {

pkg/extensions/search/resolver.go

@@ -1442,17 +1442,20 @@ func expandedRepoInfo(ctx context.Context, repo string, metaDB mTypes.MetaDB, cv
 
 	//nolint:varnamelen // standard comparison func signature
 	slices.SortFunc(dateSortedImages, func(a, b *gql_generated.ImageSummary) int {
-		// Handle nil cases: nil values are treated as oldest (come last in descending sort)
-		if a.LastUpdated == nil && b.LastUpdated == nil {
+		// Handle nil and zero time cases: both are treated as oldest (come last in descending sort)
+		aIsZero := a.LastUpdated == nil || (a.LastUpdated != nil && a.LastUpdated.IsZero())
+		bIsZero := b.LastUpdated == nil || (b.LastUpdated != nil && b.LastUpdated.IsZero())
+
+		if aIsZero && bIsZero {
 			return 0
 		}
 
-		if a.LastUpdated == nil {
-			return 1 // a is nil, b is not - a comes after b
+		if aIsZero {
+			return 1 // a is zero/nil, b is not - a comes after b
 		}
 
-		if b.LastUpdated == nil {
-			return -1 // b is nil, a is not - a comes before b
+		if bIsZero {
+			return -1 // b is zero/nil, a is not - a comes before b
 		}
 
 		if a.LastUpdated.After(*b.LastUpdated) {