3 use syntax::codemap::Spanned;
4 use utils::{span_lint_and_then, snippet};
6 /// **What it does:** Checks for operations where precedence may be unclear
7 /// and suggests to add parentheses. Currently it catches the following:
8 /// * mixed usage of arithmetic and bit shifting/combining operators without parentheses
9 /// * a "negative" numeric literal (which is really a unary `-` followed by a numeric literal)
10 /// followed by a method call
12 /// **Why is this bad?** Not everyone knows the precedence of those operators by
13 /// heart, so expressions like these may trip others trying to reason about the
16 /// **Known problems:** None.
19 /// * `1 << 2 + 3` equals 32, while `(1 << 2) + 3` equals 7
20 /// * `-1i32.abs()` equals -1, while `(-1i32).abs()` equals 1
24 "operations where precedence may be unclear"
28 pub struct Precedence;
30 impl LintPass for Precedence {
31 fn get_lints(&self) -> LintArray {
32 lint_array!(PRECEDENCE)
36 impl EarlyLintPass for Precedence {
37 fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
38 if let ExprKind::Binary(Spanned { node: op, .. }, ref left, ref right) = expr.node {
39 let span_sugg = |expr: &Expr, sugg| {
40 span_lint_and_then(cx, PRECEDENCE, expr.span, "operator precedence can trip the unwary", |db| {
41 db.span_suggestion(expr.span, "consider parenthesizing your expression", sugg);
48 match (is_arith_expr(left), is_arith_expr(right)) {
50 let sugg = format!("({}) {} ({})",
51 snippet(cx, left.span, ".."),
53 snippet(cx, right.span, ".."));
54 span_sugg(expr, sugg);
57 let sugg = format!("({}) {} {}",
58 snippet(cx, left.span, ".."),
60 snippet(cx, right.span, ".."));
61 span_sugg(expr, sugg);
64 let sugg = format!("{} {} ({})",
65 snippet(cx, left.span, ".."),
67 snippet(cx, right.span, ".."));
68 span_sugg(expr, sugg);
74 if let ExprKind::Unary(UnOp::Neg, ref rhs) = expr.node {
75 if let ExprKind::MethodCall(_, _, ref args) = rhs.node {
76 if let Some(slf) = args.first() {
77 if let ExprKind::Lit(ref lit) = slf.node {
81 LitKind::FloatUnsuffixed(..) => {
82 span_lint_and_then(cx,
85 "unary minus has lower precedence than method call",
87 db.span_suggestion(expr.span,
88 "consider adding parentheses to clarify your intent",
89 format!("-({})", snippet(cx, rhs.span, "..")));
101 fn is_arith_expr(expr: &Expr) -> bool {
103 ExprKind::Binary(Spanned { node: op, .. }, _, _) => is_arith_op(op),
108 fn is_bit_op(op: BinOpKind) -> bool {
109 use syntax::ast::BinOpKind::*;
111 BitXor | BitAnd | BitOr | Shl | Shr => true,
116 fn is_arith_op(op: BinOpKind) -> bool {
117 use syntax::ast::BinOpKind::*;
119 Add | Sub | Mul | Div | Rem => true,