rust/clippy_lints/src/double_comparison.rs
2018-03-28 15:24:26 +02:00

86 lines
2.6 KiB
Rust

//! Lint on unnecessary double comparisons. Some examples:
use rustc::hir::*;
use rustc::lint::*;
use syntax::codemap::Span;
use utils::{snippet, span_lint_and_sugg, SpanlessEq};
/// **What it does:** Checks for double comparions that could be simpified to a single expression.
///
///
/// **Why is this bad?** Readability.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// x == y || x < y
/// ```
///
/// Could be written as:
///
/// ```rust
/// x <= y
/// ```
declare_clippy_lint! {
pub DOUBLE_COMPARISONS,
complexity,
"unnecessary double comparisons that can be simplified"
}
pub struct DoubleComparisonPass;
impl LintPass for DoubleComparisonPass {
fn get_lints(&self) -> LintArray {
lint_array!(DOUBLE_COMPARISONS)
}
}
impl<'a, 'tcx> DoubleComparisonPass {
fn check_binop(
&self,
cx: &LateContext<'a, 'tcx>,
op: BinOp_,
lhs: &'tcx Expr,
rhs: &'tcx Expr,
span: Span,
) {
let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (lhs.node.clone(), rhs.node.clone()) {
(ExprBinary(lb, llhs, lrhs), ExprBinary(rb, rlhs, rrhs)) => {
(lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
}
_ => return,
};
let spanless_eq = SpanlessEq::new(cx).ignore_fn();
if !(spanless_eq.eq_expr(&llhs, &rlhs) && spanless_eq.eq_expr(&lrhs, &rrhs)) {
return;
}
macro_rules! lint_double_comparison {
($op:tt) => {{
let lhs_str = snippet(cx, llhs.span, "");
let rhs_str = snippet(cx, lrhs.span, "");
let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
span_lint_and_sugg(cx, DOUBLE_COMPARISONS, span,
"This binary expression can be simplified",
"try", sugg);
}}
}
match (op, lkind, rkind) {
(BiOr, BiEq, BiLt) | (BiOr, BiLt, BiEq) => lint_double_comparison!(<=),
(BiOr, BiEq, BiGt) | (BiOr, BiGt, BiEq) => lint_double_comparison!(>=),
(BiOr, BiLt, BiGt) | (BiOr, BiGt, BiLt) => lint_double_comparison!(!=),
(BiAnd, BiLe, BiGe) | (BiAnd, BiGe, BiLe) => lint_double_comparison!(==),
_ => (),
};
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DoubleComparisonPass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let ExprBinary(ref kind, ref lhs, ref rhs) = expr.node {
self.check_binop(cx, kind.node, lhs, rhs, expr.span);
}
}
}