C++, add support for removing index text prefixes

Closes sphinx-doc/sphinx#1958.

CHANGES

@@ -90,6 +90,8 @@ Features added
 * #2682: C++, basic support for attributes (C++11 style and GNU style).
   The new configuration variables 'cpp_id_attributes' and 'cpp_paren_attributes'
   can be used to introduce custom attributes.
+* #1958: C++, add configuration variable 'cpp_index_common_prefix' for removing
+  prefixes from the index text of C++ objects.
 
 Bugs fixed
 ----------

doc/config.rst

@@ -2006,6 +2006,13 @@ Options for the XML builder
 Options for the C++ domain
 --------------------------
 
+.. confval:: cpp_index_common_prefix
+
+   A list of prefixes that will be ignored when sorting C++ objects in the global index.
+   For example ``['awesome_lib::']``.
+
+   .. versionadded:: 1.5
+
 .. confval:: cpp_id_attributes
 
    A list of strings that the parser additionally should accept as attributes.

sphinx/domains/cpp.py

@@ -3919,7 +3919,12 @@ class CPPObject(ObjectDescription):
                       'report as bug (id=%s).' % (text_type(ast), newestId))
 
         name = text_type(ast.symbol.get_full_nested_name()).lstrip(':')
-        indexText = self.get_index_text(name)
+        strippedName = name
+        for prefix in self.env.config.cpp_index_common_prefix:
+            if name.startswith(prefix):
+                strippedName = strippedName[len(prefix):]
+                break
+        indexText = self.get_index_text(strippedName)
         self.indexnode['entries'].append(('single', indexText, newestId, '', None))
 
         if newestId not in self.state.document.ids:
@@ -4364,5 +4369,6 @@ class CPPDomain(Domain):
 
 def setup(app):
     app.add_domain(CPPDomain)
+    app.add_config_value("cpp_index_common_prefix", [], 'env')
     app.add_config_value("cpp_id_attributes", [], 'env')
     app.add_config_value("cpp_paren_attributes", [], 'env')