Add warning to manual concerning builds without testtools

Building without dune-testtools leads to missing parts in the user
manual and now raises a warning on the index page.

README.md

@@ -95,7 +95,7 @@ by CI tests.
 #### Optional Packages
 | Software | Version/Branch | Comments |
 | ---------| -------------- | -------- |
-| [dune-testtools](https://gitlab.dune-project.org/quality/dune-testtools) | releases/2.6 | Handles system tests
+| [dune-testtools](https://gitlab.dune-project.org/quality/dune-testtools) | releases/2.6 | Required for tests and parts of the user manual
 | [doxygen](http://www.stack.nl/~dimitri/doxygen/) | 1.8.13 | Builds documentation
 | [METIS](http://glaros.dtc.umn.edu/gkhome/views/metis) | 5 | For parallel runs
 | [ParMETIS](http://glaros.dtc.umn.edu/gkhome/views/metis) | 4 | For parallel runs

doc/conf.py.in

@@ -213,9 +213,14 @@ breathe_default_project = "dorie"
 
 # -- Pass special options to build setup -------------------------------------
 
+# Config: dune-testtools module was found by CMake
+meta_ini_available = "@DORIE_TESTING@".lower() in ["1", "true", "yes", "on"]
+
+# Apply custom configuration to the Sphinx app
 def setup(app):
     app.add_config_value('recommonmark_config', {
         'enable_math': True,
         'enable_inline_math': True
     }, True)
+    app.add_config_value('meta_ini_available', False, 'env')
     app.add_transform(AutoStructify)

doc/index.rst

@@ -12,6 +12,12 @@ DORiE is free software and licensed under the `GNU General Public License v3.0
 DORiE complies to `Semantic Versioning <https://semver.org/>`_. Version number
 assignment and increment are based on the :doc:`public-api`.
 
+.. ifconfig:: not meta_ini_available
+
+    .. warning::
+       This documentation was built without the ``dune-testtools`` module.
+       Example configuration files might be missing.
+
 
 .. toctree::
    :maxdepth: 2