Doxygen: set up DoxygenLayout.xml "topics" or "modules" depending on …

…doxygen version

doc/doxygen/CMakeLists.txt

@@ -114,6 +114,23 @@ configure_file(
   ${CMAKE_CURRENT_BINARY_DIR}/options.dox
   )
 
+#
+# Set up DoxygenLayout.xml. Note that the "Modules" tab has been renamed to
+# "Topics" in Doxygen 1.9.8 to avoid confusion with C++ modules.
+# Unfortunately, this requires us to play a little bit of a configuration
+# dance:
+#
+if(${DOXYGEN_VERSION} VERSION_LESS 1.9.8)
+  set(_topics_layout_flag "<tab type=\"modules\" visible=\"yes\" title=\"\" intro=\"\"/>")
+else()
+  set(_topics_layout_flag "<tab type=\"topics\" visible=\"yes\" title=\"\" intro=\"\"/>")
+endif()
+
+configure_file(
+  ${CMAKE_CURRENT_SOURCE_DIR}/DoxygenLayout.xml.in
+  ${CMAKE_CURRENT_BINARY_DIR}/DoxygenLayout.xml
+  )
+
 # Figure out the last copyright date of any of the deal.II source
 # files. We will use this then to set the copyright date of the
 # doxygen-generated HTML files.

doc/doxygen/DoxygenLayout.xml → doc/doxygen/DoxygenLayout.xml.in

@@ -5,7 +5,7 @@
     <tab type="mainpage" visible="yes" title=""/>
     <tab type="user" visible="yes" title="Tutorial" url="@ref Tutorial" />
     <tab type="user" visible="yes" title="Code gallery" url="@ref CodeGallery" />
-    <tab type="modules" visible="yes" title="" intro=""/>
+    @_topics_layout_flag@
     <tab type="namespaces" visible="yes" title="">
       <tab type="namespacelist" visible="yes" title="" intro=""/>
       <tab type="namespacemembers" visible="yes" title="" intro=""/>

doc/doxygen/options.dox.in

@@ -126,7 +126,7 @@ MATHJAX_EXTENSIONS     = TeX/AMSmath TeX/AMSsymbols
 HTML_COLORSTYLE_HUE    = 220
 HTML_COLORSTYLE_SAT    = 200
 HTML_EXTRA_STYLESHEET  = @CMAKE_CURRENT_SOURCE_DIR@/stylesheet.css
-LAYOUT_FILE            = @CMAKE_CURRENT_SOURCE_DIR@/DoxygenLayout.xml
+LAYOUT_FILE            = @CMAKE_CURRENT_BINARY_DIR@/DoxygenLayout.xml
 
 
 #---------------------------------------------------------------------------