Trigger build on default branch when saving a project

readthedocs/core/utils/__init__.py

@@ -95,7 +95,12 @@ def prepare_build(
         return (None, None)
 
     if not version:
-        version = project.versions.get(slug=LATEST)
+        default_branch = project.get_default_branch()
+        version_ = project.versions.filter(slug=default_branch)
+        if version_.exists():
+            version = version_.first()
+        else:
+            version = project.versions.get(slug=LATEST)
 
     kwargs = {
         'version_pk': version.pk,

readthedocs/rtd_tests/tests/test_core_utils.py

@@ -14,6 +14,7 @@
 from readthedocs.projects.tasks import remove_dirs
 from readthedocs.core.utils import slugify, trigger_build
 from readthedocs.projects.models import Project
+from readthedocs.builds.constants import LATEST
 
 
 class CoreUtilTests(TestCase):
@@ -33,6 +34,54 @@ def test_trigger_skipped_project(self, update_docs_task):
         self.assertEqual(result, (None, None))
         self.assertFalse(update_docs_task.signature.called)
         self.assertFalse(update_docs_task.signature().apply_async.called)
+
+    @mock.patch('readthedocs.projects.tasks.update_docs_task')
+    def test_trigger_build_when_default_branch_exists(self, update_docs_task):
+        self.assertFalse(Version.objects.filter(slug='test-slug').exists())
+
+        project_1 = get(Project)
+        version_1 = get(Version, project=project_1, slug='test-slug')
+        project_1.default_branch = 'test-slug'
+        project_1.save()
+
+        trigger_build(project=project_1)
+        kwargs = {
+            'version_pk': version_1.pk,
+            'record': True,
+            'force': False,
+            'build_pk': mock.ANY,
+        }
+
+        update_docs_task.signature.assert_has_calls([
+            mock.call(
+                args=(project_1.pk,),
+                kwargs=kwargs,
+                options=mock.ANY,
+                immutable=True,
+            ),
+        ])
+
+    @mock.patch('readthedocs.projects.tasks.update_docs_task')
+    def test_trigger_build_when_default_branch_doesnt_exist(self, update_docs_task):
+        project_1 = get(Project, default_branch=None)
+        latest_version = project_1.versions.get(slug=LATEST)
+
+        trigger_build(project=project_1)
+        kwargs = {
+            'version_pk': latest_version.pk,
+            'record': True,
+            'force': False,
+            'build_pk': mock.ANY
+        }
+
+        update_docs_task.signature.assert_has_calls([
+            mock.call(
+                args=(project_1.pk,),
+                kwargs=kwargs,
+                options=mock.ANY,
+                immutable=True,
+            ),
+        ])
 
     @mock.patch('readthedocs.projects.tasks.update_docs_task')
     def test_trigger_custom_queue(self, update_docs):