intersphinx: explicitly parse out inventory specification

tests/roots/test-ext-intersphinx-role/index.rst

@@ -20,6 +20,7 @@
 
 :external:cpp:type:`std::uint8_t`
 :external:cpp:class:`inv:foo::Bar`
+:external:cpp:func:`:inv2:foo::Bar::baz`
 
 :external:cpp:type:`FoonsTitle <foons>`
 :external:cpp:type:`inv:BarType <foons::bartype>`

tests/test_ext_intersphinx.py

@@ -558,3 +558,5 @@ def test_intersphinx_role(app):
     html = '<a class="reference external" href="http://example.org/{}" title="(in foo v2.0)">'
     for t in targets:
         assert html.format(t) in content
+
+    assert html.format('index.html#cpp_foo_bar_baz') not in content