[manpage] don't emit OSC 8 hyperlinks for anchor references (sphinx-doc#12108)

A reference like ":ref:`Some other page <some-other-page>`" results
in a refuri "#some-other-page".  This does not seem useful to readers
of the man page. It is especially unhelpful when using a terminal
that implements a hint mode for selecting links -- the extra links
add noise, making it harder to select the interesting ones.
Don't emit OSC 8 for those.
Also don't emit it for URLs that might be unsafe
(see sphinx-doc#12260 (comment))
I don't know one that would be unsafe but I'm sure there are some.

OTOH, "man_show_urls" doesn't seem unsafe because it shows the exact
URL that will be opened, so enable that for all URLs (except for
relative ones).

Follow up to sphinx-doc#12108

I also confirmed that even with docutils 0.21 we do not need to
override depart_reference because we already skip reference nodes.

Author: krobelus

sphinx/writers/manpage.py

@@ -309,7 +309,8 @@ def visit_image(self, node: Element) -> None:
     # overwritten -- don't visit inner marked up nodes
     def visit_reference(self, node: Element) -> None:
         uri = node.get('refuri', '')
-        if uri:
+        is_safe_to_click = uri.startswith(('mailto:', 'http:', 'https:', 'ftp:'))
+        if is_safe_to_click:
             # OSC 8 link start (using groff's device control directive).
             self.body.append(fr"\X'tty: link {uri}'")
 
@@ -319,7 +320,7 @@ def visit_reference(self, node: Element) -> None:
         self.visit_Text(node)
         self.body.append(self.defs['reference'][1])
 
-        if uri.startswith(('mailto:', 'http:', 'https:', 'ftp:')):
+        if not uri.startswith('#'):
             # if configured, put the URL after the link
             if self.config.man_show_urls and node.astext() != uri:
                 if uri.startswith('mailto:'):
@@ -328,7 +329,7 @@ def visit_reference(self, node: Element) -> None:
                     ' <',
                     self.defs['strong'][0], uri, self.defs['strong'][1],
                     '>'])
-        if uri:
+        if is_safe_to_click:
             # OSC 8 link end.
             self.body.append(r"\X'tty: link'")
         raise nodes.SkipNode