svg: Ensure marker-only lines get URLs

Fixes matplotlib#28595

Author: QuLogic

lib/matplotlib/backends/backend_svg.py

@@ -715,6 +715,8 @@ def draw_markers(
             self._markers[dictkey] = oid
 
         writer.start('g', **self._get_clip_attrs(gc))
+        if gc.get_url() is not None:
+            self.writer.start('a', {'xlink:href': gc.get_url()})
         trans_and_flip = self._make_flip_transform(trans)
         attrib = {'xlink:href': f'#{oid}'}
         clip = (0, 0, self.width*72, self.height*72)
@@ -726,6 +728,8 @@ def draw_markers(
                 attrib['y'] = _short_float_fmt(y)
                 attrib['style'] = self._get_style(gc, rgbFace)
                 writer.element('use', attrib=attrib)
+        if gc.get_url() is not None:
+            self.writer.end('a')
         writer.end('g')
 
     def draw_path_collection(self, gc, master_transform, paths, all_transforms,

lib/matplotlib/tests/test_backend_svg.py

@@ -343,13 +343,17 @@ def test_url():
     s.set_urls(['https://example.com/foo', 'https://example.com/bar', None])
 
     # Line2D
-    p, = plt.plot([1, 3], [6, 5])
+    p, = plt.plot([2, 3, 4], [4, 5, 6])
     p.set_url('https://example.com/baz')
 
+    # Line2D markers-only
+    p, = plt.plot([3, 4, 5], [4, 5, 6], linestyle='none', marker='x')
+    p.set_url('https://example.com/quux')
+
     b = BytesIO()
     fig.savefig(b, format='svg')
     b = b.getvalue()
-    for v in [b'foo', b'bar', b'baz']:
+    for v in [b'foo', b'bar', b'baz', b'quux']:
         assert b'https://example.com/' + v in b