Add label/author/assignee filters to the user/org home issue list (#32779)

Replace #26661, fix #25979

Not perfect, but usable and much better than before. Since it is quite
complex, I am not quite sure whether there would be any regression, if
any, I will fix in first time.

I have tested the related pages many times: issue list, milestone issue
list, project view, user issue list, org issue list.

2 files changed, 82 insertions, 6 deletions

diff --git a/routers/web/shared/issue/issue_label.go b/routers/web/shared/issue/issue_label.go
new file mode 100644
index 0000000000..eacea36b02
--- /dev/null
+++ b/routers/web/shared/issue/issue_label.go
@@ -0,0 +1,71 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package issue
+
+import (
+	"strings"
+
+	"code.gitea.io/gitea/models/db"
+	issues_model "code.gitea.io/gitea/models/issues"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/services/context"
+)
+
+// PrepareFilterIssueLabels reads the "labels" query parameter, sets `ctx.Data["Labels"]` and `ctx.Data["SelectLabels"]`
+func PrepareFilterIssueLabels(ctx *context.Context, repoID int64, owner *user_model.User) (labelIDs []int64) {
+	// 1,-2 means including label 1 and excluding label 2
+	// 0 means issues with no label
+	// blank means labels will not be filtered for issues
+	selectLabels := ctx.FormString("labels")
+	if selectLabels != "" {
+		var err error
+		labelIDs, err = base.StringsToInt64s(strings.Split(selectLabels, ","))
+		if err != nil {
+			ctx.Flash.Error(ctx.Tr("invalid_data", selectLabels), true)
+		}
+	}
+
+	var allLabels []*issues_model.Label
+	if repoID != 0 {
+		repoLabels, err := issues_model.GetLabelsByRepoID(ctx, repoID, "", db.ListOptions{})
+		if err != nil {
+			ctx.ServerError("GetLabelsByRepoID", err)
+			return nil
+		}
+		allLabels = append(allLabels, repoLabels...)
+	}
+
+	if owner != nil && owner.IsOrganization() {
+		orgLabels, err := issues_model.GetLabelsByOrgID(ctx, owner.ID, "", db.ListOptions{})
+		if err != nil {
+			ctx.ServerError("GetLabelsByOrgID", err)
+			return nil
+		}
+		allLabels = append(allLabels, orgLabels...)
+	}
+
+	// Get the exclusive scope for every label ID
+	labelExclusiveScopes := make([]string, 0, len(labelIDs))
+	for _, labelID := range labelIDs {
+		foundExclusiveScope := false
+		for _, label := range allLabels {
+			if label.ID == labelID || label.ID == -labelID {
+				labelExclusiveScopes = append(labelExclusiveScopes, label.ExclusiveScope())
+				foundExclusiveScope = true
+				break
+			}
+		}
+		if !foundExclusiveScope {
+			labelExclusiveScopes = append(labelExclusiveScopes, "")
+		}
+	}
+
+	for _, l := range allLabels {
+		l.LoadSelectedLabelsAfterClick(labelIDs, labelExclusiveScopes)
+	}
+	ctx.Data["Labels"] = allLabels
+	ctx.Data["SelectLabels"] = selectLabels
+	return labelIDs
+}
diff --git a/routers/web/shared/user/helper.go b/routers/web/shared/user/helper.go
index 7268767e0a..b82181a1df 100644
--- a/routers/web/shared/user/helper.go
+++ b/routers/web/shared/user/helper.go
@@ -8,7 +8,9 @@ import (
 	"slices"
 	"strconv"
 
+	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/optional"
 )
 
 func MakeSelfOnTop(doer *user.User, users []*user.User) []*user.User {
@@ -31,17 +33,20 @@ func MakeSelfOnTop(doer *user.User, users []*user.User) []*user.User {
 // Before, the "issue filter" passes user ID to query the list, but in many cases, it's impossible to pre-fetch the full user list.
 // So it's better to make it work like GitHub: users could input username directly.
 // Since it only converts the username to ID directly and is only used internally (to search issues), so no permission check is needed.
-// Old usage: poster=123, new usage: poster=the-username (at the moment, non-existing username is treated as poster=0, not ideal but acceptable)
-func GetFilterUserIDByName(ctx context.Context, name string) int64 {
+// Return values:
+// * nil: no filter
+// * some(id): match the id, the id could be -1 to match the issues without assignee
+// * some(NonExistingID): match no issue (due to the user doesn't exist)
+func GetFilterUserIDByName(ctx context.Context, name string) optional.Option[int64] {
 	if name == "" {
-		return 0
+		return optional.None[int64]()
 	}
 	u, err := user.GetUserByName(ctx, name)
 	if err != nil {
 		if id, err := strconv.ParseInt(name, 10, 64); err == nil {
-			return id
+			return optional.Some(id)
 		}
-		return 0
+		return optional.Some(db.NonExistingID)
 	}
-	return u.ID
+	return optional.Some(u.ID)
 }