[intersphinx] allow case-insensitive match of label-refs through intersphinx (#12033)

CHANGES.rst

@@ -84,6 +84,8 @@ Bugs fixed
   Patch by James Addison.
 * #11962: Fix target resolution when using ``:paramtype:`` fields.
   Patch by Bénédikt Tran.
+* #12008: Fix case-sensitive lookup of ``std:label`` names in intersphinx inventory.
+  Patch by Michael Goerz.
 
 Testing
 -------

sphinx/ext/intersphinx.py

@@ -334,8 +334,10 @@ def _resolve_reference_in_domain_by_target(
         if target in inventory[objtype]:
             # Case sensitive match, use it
             data = inventory[objtype][target]
-        elif objtype == 'std:term':
-            # Check for potential case insensitive matches for terms only
+        elif objtype in {'std:label', 'std:term'}:
+            # Some types require case insensitive matches:
+            # * 'term': https://github.com/sphinx-doc/sphinx/issues/9291
+            # * 'label': https://github.com/sphinx-doc/sphinx/issues/12008
             target_lower = target.lower()
             insensitive_matches = list(filter(lambda k: k.lower() == target_lower,
                                               inventory[objtype].keys()))

tests/test_extensions/test_ext_intersphinx.py

@@ -236,6 +236,16 @@ def test_missing_reference_stddomain(tmp_path, app, status, warning):
     rn = missing_reference(app, app.env, node, contnode)
     assert rn.astext() == 'A TERM'
 
+    # label reference (normal)
+    node, contnode = fake_node('std', 'ref', 'The-Julia-Domain', 'The-Julia-Domain')
+    rn = missing_reference(app, app.env, node, contnode)
+    assert rn.astext() == 'The Julia Domain'
+
+    # label reference (case insensitive)
+    node, contnode = fake_node('std', 'ref', 'the-julia-domain', 'the-julia-domain')
+    rn = missing_reference(app, app.env, node, contnode)
+    assert rn.astext() == 'The Julia Domain'
+
 
 @pytest.mark.sphinx('html', testroot='ext-intersphinx-cppdomain')
 def test_missing_reference_cppdomain(tmp_path, app, status, warning):

tests/test_util/test_util_inventory.py

@@ -41,6 +41,7 @@ foo.bar js:class 1 index.html#foo.bar -
 foo.bar.baz js:method 1 index.html#foo.bar.baz -
 foo.bar.qux js:data 1 index.html#foo.bar.qux -
 a term including:colon std:term -1 glossary.html#term-a-term-including-colon -
+The-Julia-Domain std:label -1 write_inventory/#$ The Julia Domain
 ''')
 
 inventory_v2_not_having_version = b'''\