[MODERATION] user blocking

- Add the ability to block a user via their profile page.
- This will unstar their repositories and visa versa.
- Blocked users cannot create issues or pull requests on your the doer's repositories (mind that this is not the case for organizations).
- Blocked users cannot comment on the doer's opened issues or pull requests.
- Blocked users cannot add reactions to doer's comments.
- Blocked users cannot cause a notification trough mentioning the doer.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/540
(cherry picked from commit 687d852480)
(cherry picked from commit 0c32a4fde5)

services/user/block.go

@@ -0,0 +1,40 @@
+// Copyright 2023 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+package user
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/models/db"
+	user_model "code.gitea.io/gitea/models/user"
+)
+
+// BlockUser adds a blocked user entry for userID to block blockID.
+// TODO: Figure out if instance admins should be immune to blocking.
+// TODO: Add more mechanism like removing blocked user as collaborator on
+// repositories where the user is an owner.
+func BlockUser(ctx context.Context, userID, blockID int64) error {
+	if userID == blockID || user_model.IsBlocked(ctx, userID, blockID) {
+		return nil
+	}
+
+	ctx, committer, err := db.TxContext(ctx)
+	if err != nil {
+		return err
+	}
+	defer committer.Close()
+
+	// Add the blocked user entry.
+	_, err = db.GetEngine(ctx).Insert(&user_model.BlockedUser{UserID: userID, BlockID: blockID})
+	if err != nil {
+		return err
+	}
+
+	// Unfollow the user from block's perspective.
+	err = user_model.UnfollowUser(ctx, blockID, userID)
+	if err != nil {
+		return err
+	}
+
+	return committer.Commit()
+}