rust-clippy/clippy_lints/src/precedence.rs

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use crate::utils::{in_macro, snippet_with_applicability, span_lint_and_sugg};
use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
use syntax::ast::*;
use syntax::source_map::Spanned;
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declare_clippy_lint! {
/// **What it does:** Checks for operations where precedence may be unclear
/// and suggests to add parentheses. Currently it catches the following:
/// * mixed usage of arithmetic and bit shifting/combining operators without
/// parentheses
/// * a "negative" numeric literal (which is really a unary `-` followed by a
/// numeric literal)
/// followed by a method call
///
/// **Why is this bad?** Not everyone knows the precedence of those operators by
/// heart, so expressions like these may trip others trying to reason about the
/// code.
///
/// **Known problems:** None.
///
/// **Example:**
/// * `1 << 2 + 3` equals 32, while `(1 << 2) + 3` equals 7
/// * `-1i32.abs()` equals -1, while `(-1i32).abs()` equals 1
pub PRECEDENCE,
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complexity,
"operations where precedence may be unclear"
}
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#[derive(Copy, Clone)]
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pub struct Precedence;
impl LintPass for Precedence {
fn get_lints(&self) -> LintArray {
lint_array!(PRECEDENCE)
}
fn name(&self) -> &'static str {
"Precedence"
}
}
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impl EarlyLintPass for Precedence {
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fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
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if in_macro(expr.span) {
return;
}
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if let ExprKind::Binary(Spanned { node: op, .. }, ref left, ref right) = expr.node {
let span_sugg = |expr: &Expr, sugg, appl| {
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span_lint_and_sugg(
cx,
PRECEDENCE,
expr.span,
"operator precedence can trip the unwary",
"consider parenthesizing your expression",
sugg,
appl,
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);
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};
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if !is_bit_op(op) {
return;
}
let mut applicability = Applicability::MachineApplicable;
match (is_arith_expr(left), is_arith_expr(right)) {
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(true, true) => {
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let sugg = format!(
"({}) {} ({})",
snippet_with_applicability(cx, left.span, "..", &mut applicability),
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op.to_string(),
snippet_with_applicability(cx, right.span, "..", &mut applicability)
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);
span_sugg(expr, sugg, applicability);
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},
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(true, false) => {
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let sugg = format!(
"({}) {} {}",
snippet_with_applicability(cx, left.span, "..", &mut applicability),
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op.to_string(),
snippet_with_applicability(cx, right.span, "..", &mut applicability)
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);
span_sugg(expr, sugg, applicability);
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},
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(false, true) => {
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let sugg = format!(
"{} {} ({})",
snippet_with_applicability(cx, left.span, "..", &mut applicability),
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op.to_string(),
snippet_with_applicability(cx, right.span, "..", &mut applicability)
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);
span_sugg(expr, sugg, applicability);
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},
(false, false) => (),
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}
}
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if let ExprKind::Unary(UnOp::Neg, ref rhs) = expr.node {
if let ExprKind::MethodCall(_, ref args) = rhs.node {
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if let Some(slf) = args.first() {
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if let ExprKind::Lit(ref lit) = slf.node {
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match lit.node {
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LitKind::Int(..) | LitKind::Float(..) | LitKind::FloatUnsuffixed(..) => {
let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
cx,
PRECEDENCE,
expr.span,
"unary minus has lower precedence than method call",
"consider adding parentheses to clarify your intent",
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format!(
"-({})",
snippet_with_applicability(cx, rhs.span, "..", &mut applicability)
),
applicability,
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);
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},
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_ => (),
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}
}
}
}
}
}
}
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fn is_arith_expr(expr: &Expr) -> bool {
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match expr.node {
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ExprKind::Binary(Spanned { node: op, .. }, _, _) => is_arith_op(op),
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_ => false,
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}
}
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fn is_bit_op(op: BinOpKind) -> bool {
use syntax::ast::BinOpKind::*;
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match op {
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BitXor | BitAnd | BitOr | Shl | Shr => true,
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_ => false,
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}
}
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fn is_arith_op(op: BinOpKind) -> bool {
use syntax::ast::BinOpKind::*;
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match op {
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Add | Sub | Mul | Div | Rem => true,
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_ => false,
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}
}