fix: add "xref buttons" tool panel for master view

also add `url` param for `MasterView.make_button()`

src/wuttaweb/templates/master/view.mako

@@ -33,6 +33,21 @@
   % endif
 </%def>
 
+<%def name="tool_panels()">
+  ${parent.tool_panels()}
+  ${self.tool_panel_xref()}
+</%def>
+
+<%def name="tool_panel_xref()">
+  % if xref_buttons:
+      <wutta-tool-panel heading="Cross-Reference">
+        % for button in xref_buttons:
+            ${button}
+        % endfor
+      </wutta-tool-panel>
+  % endif
+</%def>
+
 <%def name="render_vue_templates()">
   ${parent.render_vue_templates()}
   % if master.has_rows:

src/wuttaweb/views/master.py

@@ -601,6 +601,8 @@ class MasterView(View):
 
             context['rows_grid'] = grid
 
+        context['xref_buttons'] = self.get_xref_buttons(obj)
+
         return self.render_to_response('view', context)
 
     ##############################
@@ -1569,6 +1571,7 @@ class MasterView(View):
             label,
             variant=None,
             primary=False,
+            url=None,
             **kwargs,
     ):
         """
@@ -1595,10 +1598,17 @@ class MasterView(View):
            avoids the Buefy vs. Oruga confusion, and the
            implementation can change in the future.
 
+        :param url: Specify this (instead of ``href``) to make the
+           button act like a link.  This will yield something like:
+           ``<b-button tag="a" href="{url}">``
+
         :param \**kwargs: All remaining kwargs are passed to the
            underlying ``HTML.tag()`` call, so will be rendered as
            attributes on the button tag.
 
+           **NB.** You cannot specify a ``tag`` kwarg, for technical
+           reasons.
+
         :returns: HTML literal for the button element.  Will be something
            along the lines of:
 
@@ -1620,7 +1630,45 @@ class MasterView(View):
             elif primary:
                 btn_kw['type'] = 'is-primary'
 
-        return HTML.tag('b-button', **btn_kw)
+        if url:
+            btn_kw['href'] = url
+
+        button = HTML.tag('b-button', **btn_kw)
+
+        if url:
+            # nb. unfortunately HTML.tag() calls its first arg 'tag'
+            # and so we can't pass a kwarg with that name...so instead
+            # we patch that into place manually
+            button = str(button)
+            button = button.replace('<b-button ',
+                                    '<b-button tag="a" ')
+            button = HTML.literal(button)
+
+        return button
+
+    def get_xref_buttons(self, obj):
+        """
+        Should return a list of "cross-reference" buttons to be shown
+        when viewing the given object.
+
+        Default logic always returns empty list; subclass can override
+        as needed.
+
+        If applicable, this method should do its own permission checks
+        and only include the buttons current user should be allowed to
+        see/use.
+
+        See also :meth:`make_button()` - example::
+
+           def get_xref_buttons(self, product):
+               buttons = []
+               if self.request.has_perm('external_products.view'):
+                   url = self.request.route_url('external_products.view',
+                                                id=product.external_id)
+                   buttons.append(self.make_button("View External", url=url))
+               return buttons
+        """
+        return []
 
     def make_progress(self, key, **kwargs):
         """

tests/views/test_master.py

@@ -441,6 +441,12 @@ class TestMasterView(WebTestCase):
         self.assertIn('click me', html)
         self.assertIn('is-primary', html)
 
+        # with url
+        html = view.make_button('click me', url='http://example.com')
+        self.assertIn('<b-button tag="a"', html)
+        self.assertIn('click me', html)
+        self.assertIn('href="http://example.com"', html)
+
     def test_make_progress(self):
 
         # basic