include_type: honor include_type in dependency fallbacks (fixes #7503)

mesonbuild/interpreter.py

@@ -3687,9 +3687,17 @@ external dependencies (including libraries) must go to "dependencies".''')
             if not_found_message:
                 self.message_impl([not_found_message])
             raise
+        assert isinstance(d, DependencyHolder)
         if not d.found() and not_found_message:
             self.message_impl([not_found_message])
             self.message_impl([not_found_message])
+        # Ensure the correct include type
+        if 'include_type' in kwargs:
+            wanted = kwargs['include_type']
+            actual = d.include_type_method([], {})
+            if wanted != actual:
+                mlog.debug('Current include type of {} is {}. Converting to requested {}'.format(name, actual, wanted))
+                d = d.as_system_method([wanted], {})
         # Override this dependency to have consistent results in subsequent
         # dependency lookups.
         if name and d.found():

test cases/common/226 include_type dependency/meson.build

@@ -33,6 +33,9 @@ sp_dep_sys = sp_dep.as_system('system')
 assert(sp_dep_sys.include_type() == 'system', 'changing include_type works')
 assert(sp_dep.include_type() == 'preserve', 'as_system must not mutate the original object')
 
+fallback = dependency('sdffgagf_does_not_exist', include_type: 'system', fallback: ['subDep', 'subDep_dep'])
+assert(fallback.include_type() == 'system', 'include_type works with dependency fallback')
+
 # Check that PCH works with `include_type : 'system'` See https://github.com/mesonbuild/meson/issues/7167
 main_exe = executable('main_exe', 'main.cpp', cpp_pch: 'pch/test.hpp', dependencies: boost_dep)
 test('main_test', main_exe)