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Enhance RUF012 rule to handle ClassVar reassignment

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This commit is contained in:
Ruchir 2025-11-16 20:34:19 +05:30
parent 665f68036c
commit 16afe0a5bc
2 changed files with 40 additions and 8 deletions
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6
crates/ruff_linter/resources/test/fixtures/ruff/RUF012.py vendored
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@ -132,3 +132,9 @@ class AWithQuotes:
final_variable: 'Final[list[int]]' = []
class_variable_without_subscript: 'ClassVar' = []
final_variable_without_subscript: 'Final' = []
# Reassignment of a ClassVar should not trigger RUF012
class P:
class_variable: ClassVar[list] = [10, 20, 30, 40, 50]
class_variable = [*class_variable[0::1], *class_variable[2::3]]

42
crates/ruff_linter/src/rules/ruff/rules/mutable_class_default.rs
View file

@ -1,4 +1,5 @@
use ruff_python_ast::{self as ast, Stmt};
use rustc_hash::FxHashSet;
use ruff_macros::{ViolationMetadata, derive_message_formats};
use ruff_python_semantic::analyze::typing::{is_immutable_annotation, is_mutable_expr};
@ -96,7 +97,20 @@ impl Violation for MutableClassDefault {
/// RUF012
pub(crate) fn mutable_class_default(checker: &Checker, class_def: &ast::StmtClassDef) {
let mut class_var_targets: FxHashSet<String> = FxHashSet::default();
for statement in &class_def.body {
if let Stmt::AnnAssign(ast::StmtAnnAssign {
annotation, target, ..
}) = statement
{
if let ast::Expr::Name(ast::ExprName { id, .. }) = target.as_ref() {
if is_class_var_annotation(annotation, checker.semantic()) {
class_var_targets.insert(id.to_string());
}
}
}
match statement {
Stmt::AnnAssign(ast::StmtAnnAssign {
annotation,
@ -123,15 +137,27 @@ pub(crate) fn mutable_class_default(checker: &Checker, class_def: &ast::StmtClas
}
}
Stmt::Assign(ast::StmtAssign { value, targets, .. }) => {
if !targets.iter().all(is_special_attribute)
&& is_mutable_expr(value, checker.semantic())
{
// Avoid, e.g., Pydantic and msgspec models, which end up copying defaults on instance creation.
if has_default_copy_semantics(class_def, checker.semantic()) {
return;
}
if is_mutable_expr(value, checker.semantic()) {
let has_mutable_non_class_var_target = targets.iter().any(|target| {
if is_special_attribute(target) {
return false;
}
checker.report_diagnostic(MutableClassDefault, value.range());
match target {
ast::Expr::Name(ast::ExprName { id, .. }) => {
!class_var_targets.contains(id.as_str())
}
_ => true,
}
});
// Avoid, e.g., Pydantic and msgspec models, which end up copying defaults on instance creation.
if has_mutable_non_class_var_target {
if has_default_copy_semantics(class_def, checker.semantic()) {
return;
}
checker.report_diagnostic(MutableClassDefault, value.range());
}
}
}
_ => (),