Accept underline prefix when checking var-naming

examples/playbooks/role_vars_prefix_detection.yml

@@ -48,4 +48,6 @@
       ansible.builtin.include_role:
         name: role_vars_prefix_detection
       vars:
-        role_vars_prefix_detection_var2: val2
+        role_vars_prefix_detection_var1: val1
+        _role_vars_prefix_detection_var2: val2
+        __role_vars_prefix_detection_var3: val3

examples/roles/var_naming_pattern/tasks/include_task_with_vars.yml

@@ -2,7 +2,9 @@
 - name: include_task_with_vars | Foo
   ansible.builtin.include_tasks: ../tasks/included-task-with-vars.yml
   vars:
-    var_naming_pattern_foo: bar
+    var_naming_pattern_1: bar
+    _var_naming_pattern_2: ... # we allow _ before the prefix
+    __var_naming_pattern_3: ... # we allow __ before the prefix
 
 - name: include_task_with_vars | Foo
   ansible.builtin.include_role:

src/ansiblelint/rules/var_naming.md

@@ -22,7 +22,7 @@ Possible errors messages:
 - `var-naming[no-jinja]`: Variables names must not contain jinja2 templating.
 - `var-naming[pattern]`: Variables names should match ... regex.
 - `var-naming[no-role-prefix]`: Variables names from within roles should use
-  `role_name_` as a prefix.
+  `role_name_` as a prefix. Underlines are accepted before the prefix.
 - `var-naming[no-reserved]`: Variables names must not be Ansible reserved names.
 - `var-naming[read-only]`: This special variable is read-only.
 

src/ansiblelint/rules/var_naming.py

@@ -168,7 +168,7 @@ def get_var_naming_matcherror(
 
         if (
             prefix
-            and not ident.startswith(f"{prefix}_")
+            and not ident.lstrip("_").startswith(f"{prefix}_")
             and not has_jinja(prefix)
             and is_fqcn_or_name(prefix)
         ):