Re-use is_magic where possible

crates/ruff/src/rules/pep8_naming/rules/dunder_function_name.rs

@@ -3,6 +3,7 @@ use ruff_python_ast::Stmt;
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::identifier::Identifier;
+use ruff_python_semantic::analyze::visibility;
 use ruff_python_semantic::{Scope, ScopeKind};
 
 use crate::settings::types::IdentifierPattern;
@@ -51,7 +52,7 @@ pub(crate) fn dunder_function_name(
     if matches!(scope.kind, ScopeKind::Class(_)) {
         return None;
     }
-    if !(name.starts_with("__") && name.ends_with("__")) {
+    if !visibility::is_magic(name) {
         return None;
     }
     // Allowed under PEP 562 (https://peps.python.org/pep-0562/).

crates/ruff_python_semantic/src/analyze/visibility.rs

@@ -121,7 +121,7 @@ pub fn is_test(name: &str) -> bool {
 
 /// Returns `true` if a module name indicates public visibility.
 fn is_public_module(module_name: &str) -> bool {
-    !module_name.starts_with('_') || (module_name.starts_with("__") && module_name.ends_with("__"))
+    !module_name.starts_with('_') || is_magic(module_name)
 }
 
 /// Returns `true` if a module name indicates private visibility.
@@ -201,7 +201,7 @@ pub(crate) fn method_visibility(function: &ast::StmtFunctionDef) -> Visibility {
     }
 
     // Is this a magic method?
-    if function.name.starts_with("__") && function.name.ends_with("__") {
+    if is_magic(&function.name) {
         return Visibility::Public;
     }