fix: don't produce additional errors when a module is banned.

When a module is banned, an `import` statement importing the banned module causes an error, however we don't want additional errors when the module is used in the condition of some rule.

lib/src/compiler/mod.rs

@@ -1432,18 +1432,6 @@ impl<'a> Compiler<'a> {
         // Yes, module exists.
         let module = module.unwrap();
 
-        // Is the module banned? If yes, produce an error.
-        if let Some((error_title, error_msg)) =
-            self.banned_modules.get(module_name)
-        {
-            return Err(CustomError::build(
-                &self.report_builder,
-                error_title.clone(),
-                error_msg.clone(),
-                import.span().into(),
-            ));
-        }
-
         // If the module has not been added to `self.root_struct` and
         // `self.imported_modules`, do it.
         if !self.root_struct.has_field(module_name) {
@@ -1504,6 +1492,21 @@ impl<'a> Compiler<'a> {
             );
         }
 
+        // Is the module banned? If yes, produce an error. Notice however that
+        // this check is done after the module has been added to the symbol 
+        // table because we don't want additional errors due to undefined 
+        // identifiers when the banned module is used in some rule condition.
+        if let Some((error_title, error_msg)) =
+            self.banned_modules.get(module_name)
+        {
+            return Err(CustomError::build(
+                &self.report_builder,
+                error_title.clone(),
+                error_msg.clone(),
+                import.span().into(),
+            ));
+        }
+
         Ok(())
     }
 

lib/src/compiler/tests/mod.rs

@@ -595,6 +595,7 @@ fn banned_modules() {
             .add_source(
                 r#"
             import "test_proto2"
+            rule test { condition: test_proto2.int32_zero == 0}
             "#,
             )
             .expect_err("expected error")
@@ -606,6 +607,11 @@ fn banned_modules() {
   |             ^^^^^^^^^^^^^^^^^^^^ module `test_proto2` is used here
   |"#
     );
+
+    // The only error should be the error about the use of a banned module,
+    // the condition `test_proto2.int32_zero == 0` should not produce any
+    // error.
+    assert_eq!(compiler.errors().len(), 1);
 }
 
 #[cfg(feature = "test_proto2-module")]