management: Add relabel command

The command re-parses subject headers of patches from given projects
and adds label information to the database. The main usecase is to
refresh label information on existing patches after adding a new label
to the project.

Author: fstachura

docs/deployment/management.rst

@@ -192,3 +192,30 @@ patches for these new tags.
 .. option:: patch_id
 
    a patch ID number. If not supplied, all patches will be updated.
+
+.. _command-relabel:
+
+relabel
+~~~~~~~
+
+.. program:: manage.py relabel
+
+Relabel patches based on the subject line.
+
+.. code-block:: shell
+
+   ./manage.py relabel [PROJECT [PROJECT...]]
+
+Patchwork extracts labels from square brackets at the beginning of the subject
+line, eg. ``[label1, label2] Patch title``.
+
+Only labels created in the admin interface will be recognized.
+The script prioritizes project-specific labels if both project-specific and
+general labels with the same name exist.
+
+The script will not remove labels manually added to patches, but will re-add
+labels manually removed from patches.
+
+.. option:: PROJECT
+
+   list of IDs of projects to update. Relabels all projects if none specified.

patchwork/management/commands/relabel.py

@@ -0,0 +1,126 @@
+# Patchwork - automated patch tracking system
+# Copyright (C) 2026, The Linux Foundation
+#
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+from django.core.management.base import BaseCommand
+
+from email.parser import HeaderParser
+
+from patchwork.models import Label, Patch
+from patchwork.parser import clean_subject
+
+
+# Prepares a dictionary that maps from project id to a list of
+# labels of this project (including global labels, if no local version exists)
+def get_labels_per_project():
+    global_labels = list(Label.objects.filter(project_id=None).all())
+
+    labels_per_project = {}
+    for label in Label.objects.filter(project_id__isnull=True).all():
+        labels_list = labels_per_project.get(label.project_id, [])
+        labels_list.append(label)
+        labels_per_project[label.project_id] = labels_list
+
+    for project_labels in labels_per_project.values():
+        local_label_names = [label.name for label in project_labels]
+        for global_label in global_labels:
+            if global_label.name not in local_label_names:
+                project_labels.append(global_label)
+
+    return labels_per_project, global_labels
+
+
+# Parses stripped name and labels out of patch headers
+def get_name_and_labels(headers, labels):
+    parser = HeaderParser()
+    headers = parser.parsestr(headers)
+    subject = headers['Subject']
+    prefixes = []
+    if subject is None:
+        return None, None
+
+    name, prefixes, cleaned_prefixes = clean_subject(subject, labels)
+
+    return name, cleaned_prefixes
+
+
+class Command(BaseCommand):
+    help = (
+        'Update labels for existing patches based on the subject line. '
+        'NOTE: Labels have to be created in the admin interface first.'
+    )
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            'projects',
+            metavar='PROJECT',
+            nargs='*',
+            help='list of listIDs of projects to be relabeld',
+        )
+
+    def flush_patches(self):
+        if len(self.patches_to_update) > 0:
+            Patch.objects.bulk_update(self.patches_to_update, ['name'])
+            self.patches_to_update = []
+            self.patches_to_update_ids = set()
+
+        if len(self.labels_to_add) > 0:
+            Patch.labels.through.objects.bulk_create(self.labels_to_add)
+            self.labels_to_add = []
+
+    def update_patches(self, projects):
+        self.patches_to_update = []
+        self.patches_to_update_ids = set()
+        self.labels_to_add = []
+
+        query = Patch.objects.all().only('id', 'headers', 'project_id')
+
+        if projects:
+            query = query.filter(project__listid__in=projects)
+
+        count = query.count()
+
+        for i, patch in enumerate(query.iterator(chunk_size=1000)):
+            project_labels = self.labels_per_project.get(
+                patch.project_id, self.global_labels
+            )
+
+            name, cleaned_prefixes = get_name_and_labels(
+                patch.headers, [label.name for label in project_labels]
+            )
+            if name is None or cleaned_prefixes is None:
+                continue
+
+            for label in project_labels:
+                if (
+                    label.name in cleaned_prefixes
+                    and label not in patch.labels.all()
+                ):
+                    self.labels_to_add.append(
+                        Patch.labels.through(
+                            patch_id=patch.id, label_id=label.id
+                        )
+                    )
+                    if patch.id not in self.patches_to_update_ids:
+                        patch.name = name[:255]
+                        self.patches_to_update.append(patch)
+                        self.patches_to_update_ids.add(patch.id)
+
+            if (i % 100) == 0:
+                self.stdout.write('%06d/%06d\r' % (i, count), ending='')
+                self.stdout.flush()
+
+            if len(self.patches_to_update) >= 1000:
+                self.flush_patches()
+
+        self.flush_patches()
+
+    def handle(self, *args, **options):
+        self.labels_per_project, self.global_labels = get_labels_per_project()
+
+        self.stdout.write('\nupdating patches')
+
+        self.update_patches(options['projects'])
+
+        self.stdout.write('\ndone')