mintro: Fix set_variable plus assign bug (closes #5256)

mesonbuild/ast/interpreter.py

@@ -171,6 +171,7 @@ class AstInterpreter(interpreterbase.InterpreterBase):
         assert(isinstance(node, mparser.PlusAssignmentNode))
         if node.var_name not in self.assignments:
             self.assignments[node.var_name] = []
+            self.assign_vals[node.var_name] = []
         self.assignments[node.var_name] += [node.value] # Save a reference to the value node
         if hasattr(node.value, 'ast_id'):
             self.reverse_assignment[node.value.ast_id] = node

test cases/unit/55 introspection/meson.build

@@ -9,6 +9,9 @@ b2 = get_option('test_opt2')
 test_bool = b1 or b2
 test_bool = b1 and b2
 
+set_variable('list_test_plusassign', [])
+list_test_plusassign += ['bugs everywhere']
+
 if false
   dependency('somethingthatdoesnotexist', required: true)
   dependency('look_i_have_a_fallback', fallback: ['oh_no', 'the_subproject_does_not_exist'])