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list_reverse_copy.rs
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list_reverse_copy.rs
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use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Edit, Fix};
use ruff_macros::{derive_message_formats, violation};
use ruff_python_ast::{
Expr, ExprCall, ExprName, ExprSlice, ExprSubscript, ExprUnaryOp, Int, StmtAssign, UnaryOp,
};
use ruff_python_semantic::analyze::typing;
use ruff_python_semantic::SemanticModel;
use ruff_text_size::Ranged;
use crate::checkers::ast::Checker;
/// ## What it does
/// Checks for list reversals that can be performed in-place in lieu of
/// creating a new list.
///
/// ## Why is this bad?
/// When reversing a list, it's more efficient to use the in-place method
/// `.reverse()` instead of creating a new list, if the original list is
/// no longer needed.
///
/// ## Example
/// ```python
/// l = [1, 2, 3]
/// l = reversed(l)
///
/// l = [1, 2, 3]
/// l = list(reversed(l))
///
/// l = [1, 2, 3]
/// l = l[::-1]
/// ```
///
/// Use instead:
/// ```python
/// l = [1, 2, 3]
/// l.reverse()
/// ```
///
/// ## References
/// - [Python documentation: More on Lists](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists)
#[violation]
pub struct ListReverseCopy {
name: String,
}
impl AlwaysFixableViolation for ListReverseCopy {
#[derive_message_formats]
fn message(&self) -> String {
let ListReverseCopy { name } = self;
format!("Use of assignment of `reversed` on list `{name}`")
}
fn fix_title(&self) -> String {
let ListReverseCopy { name } = self;
format!("Replace with `{name}.reverse()`")
}
}
/// FURB187
pub(crate) fn list_assign_reversed(checker: &mut Checker, assign: &StmtAssign) {
let [Expr::Name(target_expr)] = assign.targets.as_slice() else {
return;
};
let Some(reversed_expr) = extract_reversed(assign.value.as_ref(), checker.semantic()) else {
return;
};
if reversed_expr.id != target_expr.id {
return;
}
let Some(binding) = checker
.semantic()
.only_binding(reversed_expr)
.map(|id| checker.semantic().binding(id))
else {
return;
};
if !typing::is_list(binding, checker.semantic()) {
return;
}
checker.diagnostics.push(
Diagnostic::new(
ListReverseCopy {
name: target_expr.id.to_string(),
},
assign.range(),
)
.with_fix(Fix::safe_edit(Edit::range_replacement(
format!("{}.reverse()", target_expr.id),
assign.range(),
))),
);
}
/// Recursively removes any `list` wrappers from the expression.
///
/// For example, given `list(list(list([1, 2, 3])))`, this function
/// would return the inner `[1, 2, 3]` expression.
fn peel_lists(expr: &Expr) -> &Expr {
let Some(ExprCall {
func, arguments, ..
}) = expr.as_call_expr()
else {
return expr;
};
if !arguments.keywords.is_empty() {
return expr;
}
if !func.as_name_expr().is_some_and(|name| name.id == "list") {
return expr;
}
let [arg] = arguments.args.as_ref() else {
return expr;
};
peel_lists(arg)
}
/// Given a call to `reversed`, returns the inner argument.
///
/// For example, given `reversed(l)`, this function would return `l`.
fn extract_name_from_reversed<'a>(
expr: &'a Expr,
semantic: &SemanticModel,
) -> Option<&'a ExprName> {
let ExprCall {
func, arguments, ..
} = expr.as_call_expr()?;
if !arguments.keywords.is_empty() {
return None;
}
let [arg] = arguments.args.as_ref() else {
return None;
};
let arg = func
.as_name_expr()
.is_some_and(|name| name.id == "reversed")
.then(|| arg.as_name_expr())
.flatten()?;
if !semantic.is_builtin("reversed") {
return None;
}
Some(arg)
}
/// Given a slice expression, returns the inner argument if it's a reversed slice.
///
/// For example, given `l[::-1]`, this function would return `l`.
fn extract_name_from_sliced_reversed(expr: &Expr) -> Option<&ExprName> {
let ExprSubscript { value, slice, .. } = expr.as_subscript_expr()?;
let ExprSlice {
lower, upper, step, ..
} = slice.as_slice_expr()?;
if lower.is_some() || upper.is_some() {
return None;
}
let Some(ExprUnaryOp {
op: UnaryOp::USub,
operand,
..
}) = step.as_ref().and_then(|expr| expr.as_unary_op_expr())
else {
return None;
};
if !operand
.as_number_literal_expr()
.and_then(|num| num.value.as_int())
.and_then(Int::as_u8)
.is_some_and(|value| value == 1)
{
return None;
};
value.as_name_expr()
}
fn extract_reversed<'a>(expr: &'a Expr, semantic: &SemanticModel) -> Option<&'a ExprName> {
let expr = peel_lists(expr);
extract_name_from_reversed(expr, semantic).or_else(|| extract_name_from_sliced_reversed(expr))
}