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| 1 | +use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Edit, Fix}; |
| 2 | +use ruff_macros::{derive_message_formats, violation}; |
| 3 | +use ruff_python_ast::{ |
| 4 | + Expr, ExprCall, ExprName, ExprSlice, ExprSubscript, ExprUnaryOp, Int, StmtAssign, UnaryOp, |
| 5 | +}; |
| 6 | +use ruff_python_semantic::analyze::typing; |
| 7 | +use ruff_python_semantic::SemanticModel; |
| 8 | +use ruff_text_size::Ranged; |
| 9 | + |
| 10 | +use crate::checkers::ast::Checker; |
| 11 | + |
| 12 | +/// ## What it does |
| 13 | +/// Checks for list reversals that can be performed in-place in lieu of |
| 14 | +/// creating a new list. |
| 15 | +/// |
| 16 | +/// ## Why is this bad? |
| 17 | +/// When reversing a list, it's more efficient to use the in-place method |
| 18 | +/// `.reverse()` instead of creating a new list, if the original list is |
| 19 | +/// no longer needed. |
| 20 | +/// |
| 21 | +/// ## Example |
| 22 | +/// ```python |
| 23 | +/// l = [1, 2, 3] |
| 24 | +/// l = reversed(l) |
| 25 | +/// |
| 26 | +/// l = [1, 2, 3] |
| 27 | +/// l = list(reversed(l)) |
| 28 | +/// |
| 29 | +/// l = [1, 2, 3] |
| 30 | +/// l = l[::-1] |
| 31 | +/// ``` |
| 32 | +/// |
| 33 | +/// Use instead: |
| 34 | +/// ```python |
| 35 | +/// l = [1, 2, 3] |
| 36 | +/// l.reverse() |
| 37 | +/// ``` |
| 38 | +/// |
| 39 | +/// ## References |
| 40 | +/// - [Python documentation: More on Lists](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists) |
| 41 | +#[violation] |
| 42 | +pub struct ListAssignReversed { |
| 43 | + name: String, |
| 44 | +} |
| 45 | + |
| 46 | +impl AlwaysFixableViolation for ListAssignReversed { |
| 47 | + #[derive_message_formats] |
| 48 | + fn message(&self) -> String { |
| 49 | + let ListAssignReversed { name } = self; |
| 50 | + format!("Use of assignment of `reversed` on list `{name}`") |
| 51 | + } |
| 52 | + |
| 53 | + fn fix_title(&self) -> String { |
| 54 | + let ListAssignReversed { name } = self; |
| 55 | + format!("Replace with `{name}.reverse()`") |
| 56 | + } |
| 57 | +} |
| 58 | + |
| 59 | +/// FURB187 |
| 60 | +pub(crate) fn list_assign_reversed(checker: &mut Checker, assign: &StmtAssign) { |
| 61 | + let [Expr::Name(target_expr)] = assign.targets.as_slice() else { |
| 62 | + return; |
| 63 | + }; |
| 64 | + |
| 65 | + let Some(reversed_expr) = extract_reversed(assign.value.as_ref(), checker.semantic()) else { |
| 66 | + return; |
| 67 | + }; |
| 68 | + |
| 69 | + if reversed_expr.id != target_expr.id { |
| 70 | + return; |
| 71 | + } |
| 72 | + |
| 73 | + let Some(binding) = checker |
| 74 | + .semantic() |
| 75 | + .only_binding(reversed_expr) |
| 76 | + .map(|id| checker.semantic().binding(id)) |
| 77 | + else { |
| 78 | + return; |
| 79 | + }; |
| 80 | + if !typing::is_list(binding, checker.semantic()) { |
| 81 | + return; |
| 82 | + } |
| 83 | + |
| 84 | + checker.diagnostics.push( |
| 85 | + Diagnostic::new( |
| 86 | + ListAssignReversed { |
| 87 | + name: target_expr.id.to_string(), |
| 88 | + }, |
| 89 | + assign.range(), |
| 90 | + ) |
| 91 | + .with_fix(Fix::safe_edit(Edit::range_replacement( |
| 92 | + format!("{}.reverse()", target_expr.id), |
| 93 | + assign.range(), |
| 94 | + ))), |
| 95 | + ); |
| 96 | +} |
| 97 | + |
| 98 | +/// Recursively removes any `list` wrappers from the expression. |
| 99 | +/// |
| 100 | +/// For example, given `list(list(list([1, 2, 3])))`, this function |
| 101 | +/// would return the inner `[1, 2, 3]` expression. |
| 102 | +fn peel_lists(expr: &Expr) -> &Expr { |
| 103 | + let Some(ExprCall { |
| 104 | + func, arguments, .. |
| 105 | + }) = expr.as_call_expr() |
| 106 | + else { |
| 107 | + return expr; |
| 108 | + }; |
| 109 | + |
| 110 | + if !arguments.keywords.is_empty() { |
| 111 | + return expr; |
| 112 | + } |
| 113 | + |
| 114 | + if !func.as_name_expr().is_some_and(|name| name.id == "list") { |
| 115 | + return expr; |
| 116 | + } |
| 117 | + |
| 118 | + let [arg] = arguments.args.as_ref() else { |
| 119 | + return expr; |
| 120 | + }; |
| 121 | + |
| 122 | + peel_lists(arg) |
| 123 | +} |
| 124 | + |
| 125 | +/// Given a call to `reversed`, returns the inner argument. |
| 126 | +/// |
| 127 | +/// For example, given `reversed(l)`, this function would return `l`. |
| 128 | +fn extract_name_from_reversed<'a>( |
| 129 | + expr: &'a Expr, |
| 130 | + semantic: &SemanticModel, |
| 131 | +) -> Option<&'a ExprName> { |
| 132 | + let ExprCall { |
| 133 | + func, arguments, .. |
| 134 | + } = expr.as_call_expr()?; |
| 135 | + |
| 136 | + if !arguments.keywords.is_empty() { |
| 137 | + return None; |
| 138 | + } |
| 139 | + |
| 140 | + let [arg] = arguments.args.as_ref() else { |
| 141 | + return None; |
| 142 | + }; |
| 143 | + |
| 144 | + let arg = func |
| 145 | + .as_name_expr() |
| 146 | + .is_some_and(|name| name.id == "reversed") |
| 147 | + .then(|| arg.as_name_expr()) |
| 148 | + .flatten()?; |
| 149 | + |
| 150 | + if !semantic.is_builtin("reversed") { |
| 151 | + return None; |
| 152 | + } |
| 153 | + |
| 154 | + Some(arg) |
| 155 | +} |
| 156 | + |
| 157 | +/// Given a slice expression, returns the inner argument if it's a reversed slice. |
| 158 | +/// |
| 159 | +/// For example, given `l[::-1]`, this function would return `l`. |
| 160 | +fn extract_name_from_sliced_reversed(expr: &Expr) -> Option<&ExprName> { |
| 161 | + let ExprSubscript { value, slice, .. } = expr.as_subscript_expr()?; |
| 162 | + let ExprSlice { |
| 163 | + lower, upper, step, .. |
| 164 | + } = slice.as_slice_expr()?; |
| 165 | + if lower.is_some() || upper.is_some() { |
| 166 | + return None; |
| 167 | + } |
| 168 | + let Some(ExprUnaryOp { |
| 169 | + op: UnaryOp::USub, |
| 170 | + operand, |
| 171 | + .. |
| 172 | + }) = step.as_ref().and_then(|expr| expr.as_unary_op_expr()) |
| 173 | + else { |
| 174 | + return None; |
| 175 | + }; |
| 176 | + if !operand |
| 177 | + .as_number_literal_expr() |
| 178 | + .and_then(|num| num.value.as_int()) |
| 179 | + .and_then(Int::as_u8) |
| 180 | + .is_some_and(|value| value == 1) |
| 181 | + { |
| 182 | + return None; |
| 183 | + }; |
| 184 | + value.as_name_expr() |
| 185 | +} |
| 186 | + |
| 187 | +fn extract_reversed<'a>(expr: &'a Expr, semantic: &SemanticModel) -> Option<&'a ExprName> { |
| 188 | + let expr = peel_lists(expr); |
| 189 | + extract_name_from_reversed(expr, semantic).or_else(|| extract_name_from_sliced_reversed(expr)) |
| 190 | +} |
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