output PACKAGE_NOT_FOUND_MESSAGE as warning when CMake package is not found

mesonbuild/dependencies/cmake.py

@@ -414,7 +414,16 @@ class CMakeDependency(ExternalDependency):
         # Whether the package is found or not is always stored in PACKAGE_FOUND
         self.is_found = self.traceparser.var_to_bool('PACKAGE_FOUND')
         if not self.is_found:
-            return
+            not_found_message = self.traceparser.get_cmake_var('PACKAGE_NOT_FOUND_MESSAGE')
+            if len(not_found_message) > 0:
+                mlog.warning(
+                    'CMake reported that the package {} was not found with the following reason:\n'
+                    '{}'.format(name, not_found_message[0]))
+            else:
+                mlog.warning(
+                    'CMake reported that the package {} was not found, '
+                    'even though Meson\'s preliminary check succeeded.'.format(name))
+            raise self._gen_exception('PACKAGE_FOUND is false')
 
         # Try to detect the version
         vers_raw = self.traceparser.get_cmake_var('PACKAGE_VERSION')

mesonbuild/dependencies/data/CMakeLists.txt

@@ -100,3 +100,9 @@ if(${_packageName}_FOUND  OR  ${PACKAGE_NAME}_FOUND)
   set(PACKAGE_DEFINITIONS  "${${definitions}}")
   set(PACKAGE_LIBRARIES    "${${libs}}")
 endif()
+
+if(${_packageName}_NOT_FOUND_MESSAGE)
+  set(PACKAGE_NOT_FOUND_MESSAGE "${${_packageName}_NOT_FOUND_MESSAGE}")
+elseif(${PACKAGE_NAME}_NOT_FOUND_MESSAGE)
+  set(PACKAGE_NOT_FOUND_MESSAGE "${${PACKAGE_NAME}_NOT_FOUND_MESSAGE}")
+endif()