gh-35536: src/sage_docbuild/conf.py: Do not fail if pplpy doc is not …

…installed

    
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### 📚 Description

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We change the sphinx configuration so that the object inventory of pplpy
is only used when it is installed.

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We currently have no way to install the pplpy documentation when using
the all-conda installation method (#35528).

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- [ ] I have updated the documentation accordingly.

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URL: #35536
Reported by: Matthias Köppe
Reviewer(s): Isuru Fernando, John H. Palmieri, Matthias Köppe

src/sage_docbuild/conf.py

@@ -231,7 +231,11 @@ def set_intersphinx_mappings(app, config):
     'python': ('https://docs.python.org/',
                 os.path.join(SAGE_DOC_SRC, "common",
                              "python{}.inv".format(python_version))),
-    'pplpy': (PPLPY_DOCS, None)}
+    }
+    if PPLPY_DOCS and os.path.exists(os.path.join(PPLPY_DOCS, 'objects.inv')):
+        app.config.intersphinx_mapping['pplpy'] = (PPLPY_DOCS, None)
+    else:
+        app.config.intersphinx_mapping['pplpy'] = ('https://www.labri.fr/perso/vdelecro/pplpy/latest/', None)
 
     # Add master intersphinx mapping
     dst = os.path.join(invpath, 'objects.inv')
@@ -925,6 +929,7 @@ def setup(app):
         app.add_config_value('intersphinx_mapping', {}, False)
         app.add_config_value('intersphinx_cache_limit', 5, False)
         app.add_config_value('intersphinx_disabled_reftypes', [], False)
+        app.add_config_value('intersphinx_timeout', None, False)
         app.connect('config-inited', set_intersphinx_mappings)
         app.connect('builder-inited', intersphinx.load_mappings)
         # We do *not* fully initialize intersphinx since we call it by hand