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use clippy_utils::diagnostics::span_lint;
use clippy_utils::ty::implements_trait;
use clippy_utils::{self, get_trait_def_id, paths};
use if_chain::if_chain;
use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for the usage of negated comparison operators on types which only implement
/// `PartialOrd` (e.g., `f64`).
///
/// ### Why is this bad?
/// These operators make it easy to forget that the underlying types actually allow not only three
/// potential Orderings (Less, Equal, Greater) but also a fourth one (Uncomparable). This is
/// especially easy to miss if the operator based comparison result is negated.
///
/// ### Example
/// ```rust
/// let a = 1.0;
/// let b = f64::NAN;
///
/// let not_less_or_equal = !(a <= b);
/// ```
///
/// Use instead:
/// ```rust
/// use std::cmp::Ordering;
/// # let a = 1.0;
/// # let b = f64::NAN;
///
/// let _not_less_or_equal = match a.partial_cmp(&b) {
/// None | Some(Ordering::Greater) => true,
/// _ => false,
/// };
/// ```
#[clippy::version = "pre 1.29.0"]
pub NEG_CMP_OP_ON_PARTIAL_ORD,
complexity,
"The use of negated comparison operators on partially ordered types may produce confusing code."
}
declare_lint_pass!(NoNegCompOpForPartialOrd => [NEG_CMP_OP_ON_PARTIAL_ORD]);
impl<'tcx> LateLintPass<'tcx> for NoNegCompOpForPartialOrd {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if_chain! {
if !in_external_macro(cx.sess(), expr.span);
if let ExprKind::Unary(UnOp::Not, inner) = expr.kind;
if let ExprKind::Binary(ref op, left, _) = inner.kind;
if let BinOpKind::Le | BinOpKind::Ge | BinOpKind::Lt | BinOpKind::Gt = op.node;
then {
let ty = cx.typeck_results().expr_ty(left);
let implements_ord = {
if let Some(id) = get_trait_def_id(cx, &paths::ORD) {
implements_trait(cx, ty, id, &[])
} else {
return;
}
};
let implements_partial_ord = {
if let Some(id) = cx.tcx.lang_items().partial_ord_trait() {
implements_trait(cx, ty, id, &[])
} else {
return;
}
};
if implements_partial_ord && !implements_ord {
span_lint(
cx,
NEG_CMP_OP_ON_PARTIAL_ORD,
expr.span,
"the use of negated comparison operators on partially ordered \
types produces code that is hard to read and refactor, please \
consider using the `partial_cmp` method instead, to make it \
clear that the two values could be incomparable"
);
}
}
}
}
}
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