C++, do not add index entries for decls in concepts

CHANGES

@@ -86,7 +86,8 @@ Bugs fixed
 * #3882: Update the order of files for HTMLHelp and QTHelp
 * #3962: sphinx-apidoc does not recognize implicit namespace packages correctly
 * #4094: C++, allow empty template argument lists.
-* C++: also hyperlink types in the name of declarations with qualified names.
+* C++, also hyperlink types in the name of declarations with qualified names.
+* C++, do not add index entries for declarations inside concepts. 
 
 Testing
 --------

sphinx/domains/cpp.py

@@ -5474,6 +5474,18 @@ class CPPObject(ObjectDescription):
                       'report as bug (id=%s).' % (text_type(ast), newestId))
 
         name = text_type(ast.symbol.get_full_nested_name()).lstrip(':')
+        # Add index entry, but not if it's a declaration inside a concept
+        isInConcept = False
+        s = ast.symbol.parent
+        while s is not None:
+            decl = s.declaration
+            s = s.parent
+            if decl is None:
+                continue
+            if decl.objectType == 'concept':
+                isInConcept = True
+                break
+        if not isInConcept:
             strippedName = name
             for prefix in self.env.config.cpp_index_common_prefix:
                 if name.startswith(prefix):