/
precedence.rs
119 lines (110 loc) · 4.29 KB
/
precedence.rs
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use rustc::lint::*;
use syntax::ast::*;
use syntax::codemap::Spanned;
use utils::{span_lint_and_sugg, snippet};
/// **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
declare_lint! {
pub PRECEDENCE,
Warn,
"operations where precedence may be unclear"
}
#[derive(Copy,Clone)]
pub struct Precedence;
impl LintPass for Precedence {
fn get_lints(&self) -> LintArray {
lint_array!(PRECEDENCE)
}
}
impl EarlyLintPass for Precedence {
fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
if let ExprKind::Binary(Spanned { node: op, .. }, ref left, ref right) = expr.node {
let span_sugg =
|expr: &Expr, sugg| {
span_lint_and_sugg(cx, PRECEDENCE, expr.span, "operator precedence can trip the unwary",
"consider parenthesizing your expression", sugg);
};
if !is_bit_op(op) {
return;
}
match (is_arith_expr(left), is_arith_expr(right)) {
(true, true) => {
let sugg = format!("({}) {} ({})",
snippet(cx, left.span, ".."),
op.to_string(),
snippet(cx, right.span, ".."));
span_sugg(expr, sugg);
},
(true, false) => {
let sugg = format!("({}) {} {}",
snippet(cx, left.span, ".."),
op.to_string(),
snippet(cx, right.span, ".."));
span_sugg(expr, sugg);
},
(false, true) => {
let sugg = format!("{} {} ({})",
snippet(cx, left.span, ".."),
op.to_string(),
snippet(cx, right.span, ".."));
span_sugg(expr, sugg);
},
(false, false) => (),
}
}
if let ExprKind::Unary(UnOp::Neg, ref rhs) = expr.node {
if let ExprKind::MethodCall(_, _, ref args) = rhs.node {
if let Some(slf) = args.first() {
if let ExprKind::Lit(ref lit) = slf.node {
match lit.node {
LitKind::Int(..) |
LitKind::Float(..) |
LitKind::FloatUnsuffixed(..) => {
span_lint_and_sugg(cx,
PRECEDENCE,
expr.span,
"unary minus has lower precedence than method call",
"consider adding parentheses to clarify your intent",
format!("-({})", snippet(cx, rhs.span, "..")));
},
_ => (),
}
}
}
}
}
}
}
fn is_arith_expr(expr: &Expr) -> bool {
match expr.node {
ExprKind::Binary(Spanned { node: op, .. }, _, _) => is_arith_op(op),
_ => false,
}
}
fn is_bit_op(op: BinOpKind) -> bool {
use syntax::ast::BinOpKind::*;
match op {
BitXor | BitAnd | BitOr | Shl | Shr => true,
_ => false,
}
}
fn is_arith_op(op: BinOpKind) -> bool {
use syntax::ast::BinOpKind::*;
match op {
Add | Sub | Mul | Div | Rem => true,
_ => false,
}
}