Add 'cpp:struct' directive and 'cpp:struct' role.

They are cosmetic variants of the class directive/role.

doc/usage/restructuredtext/domains.rst

@@ -548,11 +548,16 @@ The following directives are available. All declarations can start with a
 visibility statement (``public``, ``private`` or ``protected``).
 
 .. rst:directive:: .. cpp:class:: class specifier
+                   .. cpp:struct:: class specifier
 
    Describe a class/struct, possibly with specification of inheritance, e.g.,::
 
       .. cpp:class:: MyClass : public MyBase, MyOtherBase
 
+   The difference between :rst:dir:`cpp:class` and :rst:dir:`cpp:struct` is
+   only cosmetic: the prefix rendered in the output, and the specifier shown
+   in the index.
+
    The class can be directly declared inside a nested scope, e.g.,::
 
       .. cpp:class:: OuterScope::MyClass : public MyBase, MyOtherBase
@@ -574,6 +579,9 @@ visibility statement (``public``, ``private`` or ``protected``).
       .. cpp:class:: template<typename T> \
                      std::array<T, 42>
 
+   .. versionadded:: 2.0
+      The :rst:dir:`cpp:struct` directive.
+
 .. rst:directive:: .. cpp:function:: (member) function prototype
 
    Describe a function or member function, e.g.,::
@@ -1037,6 +1045,7 @@ These roles link to the given declaration types:
 
 .. rst:role:: cpp:any
               cpp:class
+              cpp:struct
               cpp:func
               cpp:member
               cpp:var
@@ -1048,6 +1057,9 @@ These roles link to the given declaration types:
    Reference a C++ declaration by name (see below for details).  The name must
    be properly qualified relative to the position of the link.
 
+   .. versionadded:: 2.0
+      The :rst:role:`cpp:struct` role as alias for the :rst:role:`cpp:class` role.
+
 .. admonition:: Note on References with Templates Parameters/Arguments
 
    These roles follow the Sphinx :ref:`xref-syntax` rules. This means care must be