From ae82be38cbab0b4521ac188403384b140b1e15f5 Mon Sep 17 00:00:00 2001
From: Santos Gallegos <stsewd@proton.me>
Date: Thu, 17 Apr 2025 14:48:59 -0500
Subject: [PATCH] Versions: always keep latest in sync with default branch/tag

---
 readthedocs/projects/models.py                | 14 +----
 .../projects/tests/test_build_tasks.py        |  1 +
 .../rtd_tests/tests/test_project_forms.py     | 58 ++++++++++++++++++-
 3 files changed, 58 insertions(+), 15 deletions(-)

diff --git a/readthedocs/projects/models.py b/readthedocs/projects/models.py
index 3fcad60270a..0a568d376cf 100644
--- a/readthedocs/projects/models.py
+++ b/readthedocs/projects/models.py
@@ -643,19 +643,7 @@ def save(self, *args, **kwargs):
             self.repo = self.remote_repository.clone_url
 
         super().save(*args, **kwargs)
-
-        try:
-            if not self.versions.filter(slug=LATEST).exists():
-                self.versions.create_latest()
-        except Exception:
-            log.exception("Error creating default branches")
-
-        # Update `Version.identifier` for `latest` with the default branch the user has selected,
-        # even if it's `None` (meaning to match the `default_branch` of the repository)
-        # NOTE: this code is required to be *after* ``create_latest()``.
-        # It has to be updated after creating LATEST originally.
-        log.debug("Updating default branch.", slug=LATEST, identifier=self.default_branch)
-        self.versions.filter(slug=LATEST, machine=True).update(identifier=self.default_branch)
+        self.update_latest_version()
 
     def delete(self, *args, **kwargs):
         from readthedocs.projects.tasks.utils import clean_project_resources
diff --git a/readthedocs/projects/tests/test_build_tasks.py b/readthedocs/projects/tests/test_build_tasks.py
index b9380048fc6..eed6949eac2 100644
--- a/readthedocs/projects/tests/test_build_tasks.py
+++ b/readthedocs/projects/tests/test_build_tasks.py
@@ -840,6 +840,7 @@ def test_build_commands_executed(
                     "--prune-tags",
                     "--depth",
                     "50",
+                    "refs/heads/master:refs/remotes/origin/master",
                 ),
                 mock.call(
                     "git",
diff --git a/readthedocs/rtd_tests/tests/test_project_forms.py b/readthedocs/rtd_tests/tests/test_project_forms.py
index 9b2fff1872d..59d3a1a6466 100644
--- a/readthedocs/rtd_tests/tests/test_project_forms.py
+++ b/readthedocs/rtd_tests/tests/test_project_forms.py
@@ -8,7 +8,7 @@
 from django.test.utils import override_settings
 from django_dynamic_fixture import get
 
-from readthedocs.builds.constants import EXTERNAL, LATEST, STABLE
+from readthedocs.builds.constants import EXTERNAL, LATEST, LATEST_VERBOSE_NAME, STABLE, TAG, BRANCH
 from readthedocs.builds.models import Version
 from readthedocs.core.forms import RichValidationError
 from readthedocs.oauth.models import RemoteRepository, RemoteRepositoryRelation
@@ -419,7 +419,10 @@ def test_set_remote_repository(self):
 
 class TestProjectAdvancedFormDefaultBranch(TestCase):
     def setUp(self):
-        self.project = get(Project)
+        self.project = get(
+            Project,
+            repo="https://github.com/readthedocs/readthedocs.org/",
+        )
         user_created_stable_version = get(
             Version,
             project=self.project,
@@ -530,6 +533,57 @@ def test_external_version_not_in_default_branch_choices(self):
             ],
         )
 
+    @mock.patch("readthedocs.projects.forms.trigger_build")
+    def test_change_default_branch_from_tag_to_branch_and_vice_versa(self, trigger_build):
+        branch = get(
+            Version,
+            project=self.project,
+            slug="branch",
+            type=BRANCH,
+            verbose_name="branch",
+            identifier="branch",
+        )
+        tag = get(
+            Version,
+            project=self.project,
+            slug="tag",
+            type=TAG,
+            verbose_name="tag",
+            identifier="1234abcd",
+        )
+
+        data = {
+            "name": self.project.name,
+            "repo": self.project.repo,
+            "repo_type": self.project.repo_type,
+            "default_version": LATEST,
+            "versioning_scheme": self.project.versioning_scheme,
+            "language": self.project.language,
+            "default_branch": branch.verbose_name,
+        }
+        form = UpdateProjectForm(data, instance=self.project)
+        assert form.is_valid()
+        form.save()
+
+        self.project.refresh_from_db()
+        latest = self.project.get_latest_version()
+        assert latest.slug == LATEST
+        assert latest.verbose_name == LATEST_VERBOSE_NAME
+        assert latest.identifier == branch.verbose_name
+        assert latest.type == BRANCH
+
+        data["default_branch"] = tag.verbose_name
+        form = UpdateProjectForm(data, instance=self.project)
+        assert form.is_valid()
+        form.save()
+
+        self.project.refresh_from_db()
+        latest = self.project.get_latest_version()
+        assert latest.slug == LATEST
+        assert latest.verbose_name == LATEST_VERBOSE_NAME
+        assert latest.identifier == tag.verbose_name
+        assert latest.type == TAG
+
 
 @override_settings(RTD_ALLOW_ORGANIZATIONS=False)
 class TestProjectPrevalidationForms(TestCase):