Implement a new EXTRACT_PRIVATE_VIRTUAL option.

The classic article about virtuality from Herb Sutter [1] suggests that
virtual functions are always private and public class interface is never
virtual. Until now, it was not really possible to document these
functions in Doxygen:

 * Enabling EXTRACT_PRIVATE would show all internals, not just virtual
   functions, which is not wanted.
 * Enabling HIDE_UNDOC_MEMBERS and HIDE_UNDOC_CLASSES would effectively
   disable warnings about *all* undocumented members, which is not wanted.

The usual workaround was to put the members into protected scope just
for Doxygen:

    #ifdef DOXYGEN_GENERATING_OUTPUT
    protected:
    #else
    private:
    #endif
        /** @brief Documented private virtual function */
        virtual doStuff();

The new EXTRACT_PRIVATE_VIRTUAL option makes these visible (and able to
be linked to), but shows them *only* if they are documented.

[1] http://www.gotw.ca/publications/mill18.htm

1 files changed, 35 insertions, 0 deletions

diff --git a/testing/081_extract_private_virtual.cpp b/testing/081_extract_private_virtual.cpp
new file mode 100644
index 0000000..ce4ed30
--- /dev/null
+++ b/testing/081_extract_private_virtual.cpp
@@ -0,0 +1,35 @@
+// objective: allow linking to private virtual functions
+// check: class_interface.xml
+// config: EXTRACT_PRIVATE_VIRTUAL = YES
+
+/** @brief An interface */
+class Interface {
+  public:
+    /**
+     * @brief Load things.
+     *
+     * Calls @ref doLoad().
+     */
+    void load();
+
+  private:
+    /**
+     * @brief Pure virtual implementation for @ref load()
+     *
+     * Details.
+     */
+    virtual void doLoad() = 0;
+
+    /**
+     * @brief Non-pure virtual function
+     *
+     * Details.
+     */
+    virtual void doOtherStuff();
+
+    /* Undocumented, should not appear in the docs */
+    virtual void doSomethingUndocumented();
+
+    /** @brief A non-virtual private function, not extracted */
+    void someUtility();
+};