CMake: improve error-handling for USE_*

If USE_<foo> is given a value that doesn't match **anything**,
then bail out. Since USE_* is an explicit distro choice for a
specific implementation, it's an error if that implementation
is not there.

src/modules/CMakeLists.txt

@@ -15,20 +15,23 @@ string( REPLACE " " ";" SKIP_LIST "${SKIP_MODULES}" )
 file( GLOB SUBDIRECTORIES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} "*" )
 list( SORT SUBDIRECTORIES )
 
-# Handle the USE_<foo> variables by looking for subdirectories
-# with a <foo>-<implementation> kind of name.
-foreach( SUBDIRECTORY ${SUBDIRECTORIES} )
-endforeach()
+set( _use_categories "" )
+set( _found_categories "" )
 
 foreach( SUBDIRECTORY ${SUBDIRECTORIES} )
     list( FIND SKIP_LIST ${SUBDIRECTORY} DO_SKIP )
 
     set( _skip_reason "user request" )
+    # Handle the USE_<foo> variables by looking for subdirectories
+    # with a <foo>-<implementation> kind of name.
     if( SUBDIRECTORY MATCHES "^[a-zA-Z0-9_]+-" )
         string( REGEX REPLACE "^[^-]+-" "" _implementation ${SUBDIRECTORY} )
         string( REGEX REPLACE "-.*" "" _category ${SUBDIRECTORY} )
         if( USE_${_category} )
-            if( NOT "${_implementation}" STREQUAL "${USE_${_category}}" )
+            list( APPEND _use_categories ${_category} )
+            if( "${_implementation}" STREQUAL "${USE_${_category}}" )
+                list( APPEND _found_categories ${_category} )
+            else()
                 list( APPEND SKIP_LIST ${SUBDIRECTORY} )
                 set( _skip_reason "USE_${_category}=${USE_${_category}}" )
                 set( DO_SKIP 1 )
@@ -54,5 +57,12 @@ endforeach()
 # both before and after the feature summary.
 calamares_explain_skipped_modules( ${LIST_SKIPPED_MODULES} )
 
+foreach( _category ${_use_categories} )
+    list( FIND _found_categories ${_category} _found )
+    if ( _found EQUAL -1 )
+        message( FATAL_ERROR "USE_${_category} is set to ${USE_${_category}} and no module matches." )
+    endif()
+endforeach()
+
 include( CalamaresAddTranslations )
 add_calamares_python_translations( ${CALAMARES_TRANSLATION_LANGUAGES} )