Handle open_browser trait in ServerApp and ExtensionApp differently

jupyter_server/extension/application.py

@@ -9,6 +9,7 @@
     Unicode,
     List,
     Dict,
+    Bool,
     default
 )
 from traitlets.config import Config
@@ -147,9 +148,20 @@ class method. This method can be set as a entry_point in
     # A useful class property that subclasses can override to
     # configure the underlying Jupyter Server when this extension
     # is launched directly (using its `launch_instance` method).
-    serverapp_config = {
-        "open_browser": True
-    }
+    serverapp_config = {}
+
+    # Some subclasses will likely ovrride this trait to flip
+    # the default value to True if they offer a browser
+    # based frontend.
+    open_browser = Bool(
+        False,
+        help="""Whether to open in a browser after starting.
+        The specific browser used is platform dependent and
+        determined by the python standard library `webbrowser`
+        module, unless it is overridden using the --browser
+        (ServerApp.browser) configuration option.
+        """
+    ).tag(config=True)
 
     # The extension name used to name the jupyter config
     # file, jupyter_{name}_config.
@@ -365,6 +377,8 @@ def initialize_server(cls, argv=[], load_other_extensions=True, **kwargs):
         config = Config(cls._jupyter_server_config())
         serverapp = ServerApp.instance(**kwargs, argv=[], config=config)
         serverapp.initialize(argv=argv, find_extensions=load_other_extensions)
+        # Inform the serverapp that this extension app started the app.
+        serverapp._starter_app_name = cls.name
         return serverapp
 
     def initialize(self):

jupyter_server/serverapp.py

@@ -887,6 +887,28 @@ def _default_allow_remote(self):
        """
     )
 
+    # The name of the app that started this server (if not started directly).
+    # It is sometimes important to know if + which another app (say a server extension)
+    # started the serverapp to properly configure some traits.
+    # This trait should not be configured by users. It will likely be set by ExtensionApp.
+    _starter_app_name = Unicode(None, allow_none=True)
+
+    @validate('_starter_app_name')
+    def _validate_starter_app(self, proposal):
+        # Check that a previous server extension isn't named yet
+        value = proposal["value"]
+        if self._starter_app_name != None:
+            raise TraitError("Another extension was already named as the starter_server_extension.")
+        return value
+
+    @property
+    def starter_app(self):
+        """Get the Extension that started this server."""
+        name = self._starter_app_name
+        if name is None:
+            return
+        return self.extension_manager.extension_points.get(name, None).app
+
     open_browser = Bool(False, config=True,
                         help="""Whether to open in a browser after starting.
                         The specific browser used is platform dependent and
@@ -895,6 +917,31 @@ def _default_allow_remote(self):
                         (ServerApp.browser) configuration option.
                         """)
 
+
+    def _handle_browser_opening(self):
+        """This method handles whether a browser should be opened.
+        By default, Jupyter Server doesn't try to open an browser. However,
+        it's many server extensions might want to open the browser by default.
+        This essentially toggles the default value for open_browser.
+
+        From a UX perspective, this needs to be surfaced to the user. The default
+        behavior of Jupyter Server switches, which can be confusing.
+        """
+        # If the server was started by another application, use that applications
+        # trait for the open_browser trait. If that trait is not given, ignore
+        if self.starter_app:
+            try:
+                if self.starter_app.open_browser:
+                    self.launch_browser()
+            # If the starter_app doesn't have an open_browser trait, ignore
+            # move on and don't start a browser.
+            except AttributeError:
+                pass
+        else:
+            if self.open_browser:
+                self.launch_browser()
+
+
     browser = Unicode(u'', config=True,
                       help="""Specify what command to use to invoke a web
                       browser when starting the server. If not specified, the
@@ -1807,8 +1854,8 @@ def start_app(self):
         self.write_server_info_file()
         self.write_browser_open_file()
 
-        if self.open_browser:
-            self.launch_browser()
+        # Handle the browser opening.
+        self._handle_browser_opening()
 
         if self.token and self._token_generated:
             # log full URL with generated token, so there's a copy/pasteable link