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

2 files changed, 145 insertions, 0 deletions

diff --git a/testing/081/class_interface.xml b/testing/081/class_interface.xml
new file mode 100644
index 0000000..2385b86
--- /dev/null
+++ b/testing/081/class_interface.xml
@@ -0,0 +1,110 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<doxygen xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="compound.xsd" version="">
+  <compounddef id="class_interface" kind="class" language="C++" prot="public" abstract="yes">
+    <compoundname>Interface</compoundname>
+    <sectiondef kind="public-func">
+      <memberdef kind="function" id="class_interface_1ab58d3008a7001cbb47f2fa5a5a1aeefa" prot="public" static="no" const="no" explicit="no" inline="no" virt="non-virtual">
+        <type>void</type>
+        <definition>void Interface::load</definition>
+        <argsstring>()</argsstring>
+        <name>load</name>
+        <briefdescription>
+          <para>Load things. </para>
+        </briefdescription>
+        <detaileddescription>
+          <para>Calls <ref refid="class_interface_1a328e0a16ccee5d796ca93801a055d27d" kindref="member">doLoad()</ref>. </para>
+        </detaileddescription>
+        <inbodydescription>
+        </inbodydescription>
+        <location file="081_extract_private_virtual.cpp" line="13" column="1"/>
+      </memberdef>
+    </sectiondef>
+    <sectiondef kind="private-func">
+      <memberdef kind="function" id="class_interface_1a328e0a16ccee5d796ca93801a055d27d" prot="private" static="no" const="no" explicit="no" inline="no" virt="pure-virtual">
+        <type>void</type>
+        <definition>virtual void Interface::doLoad</definition>
+        <argsstring>()=0</argsstring>
+        <name>doLoad</name>
+        <briefdescription>
+          <para>Pure virtual implementation for <ref refid="class_interface_1ab58d3008a7001cbb47f2fa5a5a1aeefa" kindref="member">load()</ref> </para>
+        </briefdescription>
+        <detaileddescription>
+          <para>Details. </para>
+        </detaileddescription>
+        <inbodydescription>
+        </inbodydescription>
+        <location file="081_extract_private_virtual.cpp" line="21" column="1"/>
+      </memberdef>
+      <memberdef kind="function" id="class_interface_1ad13fffb1181ab0da1f8fbb586eff9afe" prot="private" static="no" const="no" explicit="no" inline="no" virt="virtual">
+        <type>void</type>
+        <definition>virtual void Interface::doOtherStuff</definition>
+        <argsstring>()</argsstring>
+        <name>doOtherStuff</name>
+        <briefdescription>
+          <para>Non-pure virtual function. </para>
+        </briefdescription>
+        <detaileddescription>
+          <para>Details. </para>
+        </detaileddescription>
+        <inbodydescription>
+        </inbodydescription>
+        <location file="081_extract_private_virtual.cpp" line="28" column="1"/>
+      </memberdef>
+      <memberdef kind="function" id="class_interface_1a46062977049a7c2c2c141e4487e954b8" prot="private" static="no" const="no" explicit="no" inline="no" virt="virtual">
+        <type>void</type>
+        <definition>virtual void Interface::doSomethingUndocumented</definition>
+        <argsstring>()</argsstring>
+        <name>doSomethingUndocumented</name>
+        <briefdescription>
+        </briefdescription>
+        <detaileddescription>
+        </detaileddescription>
+        <inbodydescription>
+        </inbodydescription>
+        <location file="081_extract_private_virtual.cpp" line="31" column="1"/>
+      </memberdef>
+      <memberdef kind="function" id="class_interface_1a108dce1debd0596b57e7985bbb0f63a1" prot="private" static="no" const="no" explicit="no" inline="no" virt="non-virtual">
+        <type>void</type>
+        <definition>void Interface::someUtility</definition>
+        <argsstring>()</argsstring>
+        <name>someUtility</name>
+        <briefdescription>
+          <para>A non-virtual private function, not extracted. </para>
+        </briefdescription>
+        <detaileddescription>
+        </detaileddescription>
+        <inbodydescription>
+        </inbodydescription>
+        <location file="081_extract_private_virtual.cpp" line="34" column="1"/>
+      </memberdef>
+    </sectiondef>
+    <briefdescription>
+      <para>An interface. </para>
+    </briefdescription>
+    <detaileddescription>
+    </detaileddescription>
+    <location file="081_extract_private_virtual.cpp" line="6" column="1" bodyfile="081_extract_private_virtual.cpp" bodystart="6" bodyend="35"/>
+    <listofallmembers>
+      <member refid="class_interface_1a328e0a16ccee5d796ca93801a055d27d" prot="private" virt="pure-virtual">
+        <scope>Interface</scope>
+        <name>doLoad</name>
+      </member>
+      <member refid="class_interface_1ad13fffb1181ab0da1f8fbb586eff9afe" prot="private" virt="virtual">
+        <scope>Interface</scope>
+        <name>doOtherStuff</name>
+      </member>
+      <member refid="class_interface_1a46062977049a7c2c2c141e4487e954b8" prot="private" virt="virtual">
+        <scope>Interface</scope>
+        <name>doSomethingUndocumented</name>
+      </member>
+      <member refid="class_interface_1ab58d3008a7001cbb47f2fa5a5a1aeefa" prot="public" virt="non-virtual">
+        <scope>Interface</scope>
+        <name>load</name>
+      </member>
+      <member refid="class_interface_1a108dce1debd0596b57e7985bbb0f63a1" prot="private" virt="non-virtual">
+        <scope>Interface</scope>
+        <name>someUtility</name>
+      </member>
+    </listofallmembers>
+  </compounddef>
+</doxygen>
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();
+};