123 lines
4.5 KiB
Rust
123 lines
4.5 KiB
Rust
use rustc::lint::*;
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use syntax::ast::*;
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use syntax::codemap::Spanned;
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use utils::{span_lint, snippet};
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/// **What it does:** Checks for operations where precedence may be unclear
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/// and suggests to add parentheses. Currently it catches the following:
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/// * mixed usage of arithmetic and bit shifting/combining operators without parentheses
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/// * a "negative" numeric literal (which is really a unary `-` followed by a numeric literal)
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/// followed by a method call
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///
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/// **Why is this bad?** Not everyone knows the precedence of those operators by
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/// heart, so expressions like these may trip others trying to reason about the
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/// code.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// * `1 << 2 + 3` equals 32, while `(1 << 2) + 3` equals 7
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/// * `-1i32.abs()` equals -1, while `(-1i32).abs()` equals 1
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declare_lint! {
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pub PRECEDENCE,
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Warn,
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"operations where precedence may be unclear"
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}
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#[derive(Copy,Clone)]
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pub struct Precedence;
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impl LintPass for Precedence {
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fn get_lints(&self) -> LintArray {
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lint_array!(PRECEDENCE)
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}
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}
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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 let ExprKind::Binary(Spanned { node: op, .. }, ref left, ref right) = expr.node {
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if !is_bit_op(op) {
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return;
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}
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match (is_arith_expr(left), is_arith_expr(right)) {
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(true, true) => {
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span_lint(cx,
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PRECEDENCE,
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expr.span,
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&format!("operator precedence can trip the unwary. Consider parenthesizing your \
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expression:`({}) {} ({})`",
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snippet(cx, left.span, ".."),
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op.to_string(),
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snippet(cx, right.span, "..")));
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}
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(true, false) => {
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span_lint(cx,
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PRECEDENCE,
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expr.span,
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&format!("operator precedence can trip the unwary. Consider parenthesizing your \
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expression:`({}) {} {}`",
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snippet(cx, left.span, ".."),
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op.to_string(),
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snippet(cx, right.span, "..")));
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}
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(false, true) => {
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span_lint(cx,
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PRECEDENCE,
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expr.span,
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&format!("operator precedence can trip the unwary. Consider parenthesizing your \
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expression:`{} {} ({})`",
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snippet(cx, left.span, ".."),
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op.to_string(),
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snippet(cx, right.span, "..")));
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}
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_ => (),
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}
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}
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if let ExprKind::Unary(UnOp::Neg, ref rhs) = expr.node {
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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(..) |
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LitKind::Float(..) |
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LitKind::FloatUnsuffixed(..) => {
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span_lint(cx,
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PRECEDENCE,
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expr.span,
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&format!("unary minus has lower precedence than method call. Consider \
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adding parentheses to clarify your intent: -({})",
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snippet(cx, rhs.span, "..")));
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}
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_ => (),
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}
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}
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}
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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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}
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fn is_bit_op(op: BinOpKind) -> bool {
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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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}
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fn is_arith_op(op: BinOpKind) -> bool {
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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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}
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}
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