docs(dev): the viewer is a library, not an app

developer_manual/basics/events.rst

@@ -384,13 +384,6 @@ This event is triggered right after the LDAP group backend is registered.
 
 This event is triggered right after the LDAP user backend is registered.
 
-``\OCA\Viewer\Event\LoadViewer``
-********************************
-
-.. versionadded:: 17
-
-This event is triggered whenever the viewer is loaded and extensions should be loaded.
-
 .. include:: _available_events_ocp.rst
 
 Hooks

developer_manual/client_apis/OCS/ocs-api-overview.rst

@@ -179,6 +179,36 @@ Clients can obtain capabilities provided by the Nextcloud server and its apps vi
     </ocs>
 
 
+.. _preview-capabilities:
+
+Preview capabilities
+--------------------
+
+.. versionadded:: 36
+
+The mime types the server can render a preview for. A client uses it to tell the formats a
+browser cannot display on its own, but the server can render, from the ones it can do neither
+of: ``image/heic``, ``image/heif`` and ``image/tiff`` are viewable through a preview and not
+otherwise.
+
+Each entry is the mime pattern a provider registered itself for, as a regular expression
+delimited by slashes. The list is empty when previews are turned off entirely
+(``enable_previews``), which means no preview can be requested for any file.
+
+.. code:: json
+
+    {
+        "core": {
+            "previews": {
+                "enabled_providers": [
+                    "/image\\/png/",
+                    "/image\\/jpeg/",
+                    "/image\\/hei(f|c)/"
+                ]
+            }
+        }
+    }
+
 Theming capabilities
 --------------------
 

developer_manual/getting_started/devenv.rst

@@ -87,23 +87,6 @@ or::
 
 Now access the installation at http://localhost/ (or the corresponding URL) in your web browser to set up your instance.
 
-Check out external shipped apps
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-This optional step is especially necessary if you want to test upgrading, as the following apps are required to be present during an upgrade.
-
-Install the viewer app::
-
-  cd /var/www/apps
-  git clone https://github.com/nextcloud/viewer.git
-
-Make sure to use a version compatible with the server by checking out the matching tag.
-You can check the ``appinfo/info.xml`` of the app to see if its ``min-version`` field is compatible with the current server.
-
-When upgrading the server code you might need to upgrade the app code as well before running ``occ upgrade``.
-
-.. note:: The same applies to all the apps listed under ``alwaysEnabled`` in `shipped.json <https://github.com/nextcloud/server/blob/master/core/shipped.json#L49>`_ but most are already present in the server repository.
-
 .. _debugmode:
 
 Enabling debug mode

developer_manual/release_notes/critical_changes.rst

@@ -89,6 +89,82 @@ Make sure to adjust your CI matrix for testing with them. This is automatically
 
   .. note:: MySQL 9+ deprecated support for MD5, so we strongly recommend to migrate away from the MD5 SQL function in your apps.
 
+The Viewer is a library, not an app
+-----------------------------------
+
+The ``viewer`` app has been removed from Nextcloud 36. The viewer itself now ships as the
+`@nextcloud/viewer <https://www.npmjs.com/package/@nextcloud/viewer>`_ library, which any app
+can depend on:
+
+.. code-block:: bash
+
+    npm install --save @nextcloud/viewer
+
+Importing it registers the handlers for images, video and audio, and offers this copy of the
+viewer to the page. Several apps on one page may each bring their own copy: they elect the
+newest between them, and only that one is ever loaded, the first time a file is opened.
+
+Registering a handler
+^^^^^^^^^^^^^^^^^^^^^
+
+Register handlers from a script loaded with ``\OCP\Util::addInitScript()``. The Files list
+reads the available actions when it first renders, so a handler registered after that is a
+file that does not open.
+
+.. code-block:: javascript
+
+    import { registerHandler } from '@nextcloud/viewer'
+
+    registerHandler({
+        id: 'my-app',
+        displayName: t('my_app', 'My files'),
+        // A custom element you define yourself, and which receives the file to show
+        tagname: 'my-app-viewer',
+        enabled: (nodes) => nodes.every((node) => node.mime === 'application/x-my-format'),
+    })
+
+Opening the viewer
+^^^^^^^^^^^^^^^^^^
+
+``OCA.Viewer`` is gone, along with the ``\OCA\Viewer\Event\LoadViewer`` event apps
+dispatched to ask the app to load itself. Nothing needs to be dispatched any more; ask the
+service for the viewer and hand it nodes:
+
+.. code-block:: javascript
+
+    import { canView, getViewer } from '@nextcloud/viewer'
+
+    // OCA.Viewer.open({ path }) becomes, with `node` an INode from @nextcloud/files:
+    getViewer().open([node], node)
+
+    // OCA.Viewer.mimetypes.includes(node.mime) becomes:
+    canView(node)
+
+The first argument is the list to page through, the second the file to open. ``compare(a, b)``
+replaces ``OCA.Viewer.compare()``, and ``open()`` takes options as a third argument, among them
+``enableSidebar`` for a file the Files sidebar cannot resolve.
+
+``OCA.Viewer.setRootElement()`` has no replacement. It rendered a single file into an element
+of your choosing instead of the modal, and the only known user was a public share page. Show a
+preview of the file there and let a click on it call ``open()``.
+
+The full handler API is documented with the library.
+
+Enabled preview providers
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The viewer app provided the enabled preview providers as an initial state, which apps could
+read with ``loadState('viewer', 'enabled_preview_providers')``. It is a capability now, so it
+is available wherever capabilities are, public share pages included:
+
+.. code-block:: javascript
+
+    import { getCapabilities } from '@nextcloud/capabilities'
+
+    getCapabilities().core.previews.enabled_providers
+
+See :ref:`preview-capabilities` for what it contains.
+
 Removed front-end APIs and libraries
 ------------------------------------