Add before_{create,edit,delete}_snippet hooks

CHANGELOG.txt

@@ -4,6 +4,7 @@ Changelog
 2.11 (xx.xx.xxxx) - IN DEVELOPMENT
 ~~~~~~~~~~~~~~~~~
 
+ * Add `before_edit_snippet`, `before_create_snippet` and `before_delete_snippet` hooks and documentation (Karl Hobley. Sponsored by the Mozilla Foundation)
 
 2.10 (xx.xx.xxxx) - IN DEVELOPMENT
 ~~~~~~~~~~~~~~~~~

docs/reference/hooks.rst

@@ -1016,6 +1016,24 @@ Hooks for working with registered Snippets.
     def after_snippet_update(request, instance):
         return HttpResponse(f"Congrats on editing a snippet with id {instance.pk}", content_type="text/plain")
 
+.. _before_edit_snippet:
+
+``before_edit_snippet``
+~~~~~~~~~~~~~~~~~~~~~~
+
+  Called at the beginning of the edit snippet view. The callable passed into the hook will receive the model instance, the request object. If the callable returns an ``HttpResponse``, that response will be returned immediately to the user, and Wagtail will not proceed to call ``redirect()`` to the listing view.
+
+  .. code-block:: python
+
+    from django.http import HttpResponse
+
+    from wagtail.core import hooks
+
+    @hooks.register('before_edit_snippet')
+    def block_snippet_edit(request, instance):
+        if isinstance(instance, RestrictedSnippet) and instance.prevent_edit:
+            return HttpResponse("Sorry, you can't edit this snippet", content_type="text/plain")
+
 .. _after_create_snippet:
 
 ``after_create_snippet``
@@ -1025,6 +1043,13 @@ Hooks for working with registered Snippets.
   ``after_edit_snippet`` work in identical ways. The only difference is where
   the hook is called.
 
+.. _before_create_snippet:
+
+``before_create_snippet``
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+  Called at the beginning of the create snippet view. Works in a similar way to `before_edit_snippet` except the model is passed as an argument instead of an instance.
+
 .. _after_delete_snippet:
 
 ``after_delete_snippet``
@@ -1044,6 +1069,29 @@ Hooks for working with registered Snippets.
         total = len(instances)
         return HttpResponse(f"{total} snippets have been deleted", content_type="text/plain")
 
+.. _before_delete_snippet:
+
+``before_delete_snippet``
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+  Called at the beginning of the delete snippet view. The callable passed into the hook will receive the model instance(s) as a queryset along with the request object. If the callable returns an ``HttpResponse``, that response will be returned immediately to the user, and Wagtail will not proceed to call ``redirect()`` to the listing view.
+
+  .. code-block:: python
+
+    from django.http import HttpResponse
+
+    from wagtail.core import hooks
+
+    @hooks.register('before_delete_snippet')
+    def before_snippet_delete(request, instances):
+        # "instances" is a QuerySet
+        total = len(instances)
+
+        if request.method == 'POST':
+          # Override the deletion behaviour
+          instances.delete()
+
+          return HttpResponse(f"{total} snippets have been deleted", content_type="text/plain")
 
 Audit log
 ---------

docs/releases/2.11.rst

@@ -13,7 +13,7 @@ What's new
 Other features
 ~~~~~~~~~~~~~~
 
- * ...
+ * Add ``before_edit_snippet``, ``before_create_snippet`` and ``before_delete_snippet`` hooks and documentation (Karl Hobley. Sponsored by the Mozilla Foundation)
 
 
 Bug fixes

wagtail/snippets/tests.py

@@ -228,6 +228,37 @@ class TestSnippetCreateView(TestCase, WagtailTestUtils):
         snippet = FileUploadSnippet.objects.get()
         self.assertEqual(snippet.file.read(), b"Uploaded file")
 
+    def test_before_create_snippet_hook_get(self):
+        def hook_func(request, model):
+            self.assertIsInstance(request, HttpRequest)
+            self.assertEqual(model, Advert)
+            return HttpResponse("Overridden!")
+
+        with self.register_hook('before_create_snippet', hook_func):
+            response = self.get()
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.content, b"Overridden!")
+
+    def test_before_create_snippet_hook_post(self):
+        def hook_func(request, model):
+            self.assertIsInstance(request, HttpRequest)
+            self.assertEqual(model, Advert)
+            return HttpResponse("Overridden!")
+
+        with self.register_hook('before_create_snippet', hook_func):
+            post_data = {
+                'text': 'Hook test',
+                'url': 'http://www.example.com/'
+            }
+            response = self.post(post_data=post_data)
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.content, b"Overridden!")
+
+        # Request intercepted before advert was created
+        self.assertFalse(Advert.objects.exists())
+
     def test_after_create_snippet_hook(self):
         def hook_func(request, instance):
             self.assertIsInstance(request, HttpRequest)
@@ -245,6 +276,9 @@ class TestSnippetCreateView(TestCase, WagtailTestUtils):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.content, b"Overridden!")
 
+        # Request intercepted after advert was created
+        self.assertTrue(Advert.objects.exists())
+
 
 class BaseTestSnippetEditView(TestCase, WagtailTestUtils):
 
@@ -318,6 +352,38 @@ class TestSnippetEditView(BaseTestSnippetEditView):
             list(snippet.tags.order_by('name')),
             expected_tags)
 
+    def test_before_edit_snippet_hook_get(self):
+
+        def hook_func(request, instance):
+            self.assertIsInstance(request, HttpRequest)
+            self.assertEqual(instance.text, 'test_advert')
+            self.assertEqual(instance.url, 'http://www.example.com')
+            return HttpResponse("Overridden!")
+
+        with self.register_hook('before_edit_snippet', hook_func):
+            response = self.get()
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.content, b"Overridden!")
+
+    def test_before_edit_snippet_hook_post(self):
+
+        def hook_func(request, instance):
+            self.assertIsInstance(request, HttpRequest)
+            self.assertEqual(instance.text, 'test_advert')
+            self.assertEqual(instance.url, 'http://www.example.com')
+            return HttpResponse("Overridden!")
+
+        with self.register_hook('before_edit_snippet', hook_func):
+            response = self.post(post_data={'text': 'Edited and runs hook',
+                                            'url': 'http://www.example.com/hook-enabled-edited'})
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.content, b"Overridden!")
+
+        # Request intercepted before advert was updated
+        self.assertEqual(Advert.objects.get().text, "test_advert")
+
     def test_after_edit_snippet_hook(self):
 
         def hook_func(request, instance):
@@ -333,6 +399,9 @@ class TestSnippetEditView(BaseTestSnippetEditView):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.content, b"Overridden!")
 
+        # Request intercepted after advert was updated
+        self.assertEqual(Advert.objects.get().text, "Edited and runs hook")
+
 
 class TestEditTabbedSnippet(BaseTestSnippetEditView):
 
@@ -402,6 +471,45 @@ class TestSnippetDelete(TestCase, WagtailTestUtils):
         self.assertContains(response, 'Used 2 times')
         self.assertContains(response, self.test_snippet.usage_url())
 
+    def test_before_delete_snippet_hook_get(self):
+        advert = Advert.objects.create(
+            url='http://www.example.com/',
+            text='Test hook',
+        )
+
+        def hook_func(request, instances):
+            self.assertIsInstance(request, HttpRequest)
+            self.assertQuerysetEqual(instances, ["<Advert: Test hook>"])
+            return HttpResponse("Overridden!")
+
+        with self.register_hook('before_delete_snippet', hook_func):
+            response = self.client.get(reverse('wagtailsnippets:delete', args=['tests', 'advert', quote(advert.pk)]))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.content, b"Overridden!")
+
+    def test_before_delete_snippet_hook_post(self):
+        advert = Advert.objects.create(
+            url='http://www.example.com/',
+            text='Test hook',
+        )
+
+        def hook_func(request, instances):
+            self.assertIsInstance(request, HttpRequest)
+            self.assertQuerysetEqual(instances, ["<Advert: Test hook>"])
+            return HttpResponse("Overridden!")
+
+        with self.register_hook('before_delete_snippet', hook_func):
+            response = self.client.post(
+                reverse('wagtailsnippets:delete', args=('tests', 'advert', quote(advert.pk), ))
+            )
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.content, b"Overridden!")
+
+        # Request intercepted before advert was deleted
+        self.assertTrue(Advert.objects.filter(pk=advert.pk).exists())
+
     def test_after_delete_snippet_hook(self):
         advert = Advert.objects.create(
             url='http://www.example.com/',
@@ -421,6 +529,9 @@ class TestSnippetDelete(TestCase, WagtailTestUtils):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.content, b"Overridden!")
 
+        # Request intercepted after advert was deleted
+        self.assertFalse(Advert.objects.filter(pk=advert.pk).exists())
+
 
 class TestSnippetDeleteMultipleWithOne(TestCase, WagtailTestUtils):
     # test deletion of one snippet using the delete-multiple URL

wagtail/snippets/views/snippets.py

@@ -134,6 +134,11 @@ def create(request, app_label, model_name):
     if not request.user.has_perm(permission):
         return permission_denied(request)
 
+    for fn in hooks.get_hooks('before_create_snippet'):
+        result = fn(request, model)
+        if hasattr(result, 'status_code'):
+            return result
+
     instance = model()
     edit_handler = get_snippet_edit_handler(model)
     edit_handler = edit_handler.bind_to(request=request)
@@ -188,6 +193,12 @@ def edit(request, app_label, model_name, pk):
         return permission_denied(request)
 
     instance = get_object_or_404(model, pk=unquote(pk))
+
+    for fn in hooks.get_hooks('before_edit_snippet'):
+        result = fn(request, instance)
+        if hasattr(result, 'status_code'):
+            return result
+
     edit_handler = get_snippet_edit_handler(model)
     edit_handler = edit_handler.bind_to(instance=instance, request=request)
     form_class = edit_handler.get_form_class()
@@ -247,6 +258,11 @@ def delete(request, app_label, model_name, pk=None):
         ids = request.GET.getlist('id')
         instances = model.objects.filter(pk__in=ids)
 
+    for fn in hooks.get_hooks('before_delete_snippet'):
+        result = fn(request, instances)
+        if hasattr(result, 'status_code'):
+            return result
+
     count = len(instances)
 
     if request.method == 'POST':