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use clippy_utils::diagnostics::span_lint;
use clippy_utils::eq_expr_value;
use clippy_utils::source::snippet;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks for explicit self-assignments.
///
/// **Why is this bad?** Self-assignments are redundant and unlikely to be
/// intentional.
///
/// **Known problems:** If expression contains any deref coercions or
/// indexing operations they are assumed not to have any side effects.
///
/// **Example:**
///
/// ```rust
/// struct Event {
/// id: usize,
/// x: i32,
/// y: i32,
/// }
///
/// fn copy_position(a: &mut Event, b: &Event) {
/// a.x = b.x;
/// a.y = a.y;
/// }
/// ```
pub SELF_ASSIGNMENT,
correctness,
"explicit self-assignment"
}
declare_lint_pass!(SelfAssignment => [SELF_ASSIGNMENT]);
impl<'tcx> LateLintPass<'tcx> for SelfAssignment {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::Assign(lhs, rhs, _) = &expr.kind {
if eq_expr_value(cx, lhs, rhs) {
let lhs = snippet(cx, lhs.span, "<lhs>");
let rhs = snippet(cx, rhs.span, "<rhs>");
span_lint(
cx,
SELF_ASSIGNMENT,
expr.span,
&format!("self-assignment of `{}` to `{}`", rhs, lhs),
);
}
}
}
}
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