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use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::ty::is_type_diagnostic_item;
use rustc_hir::{CaptureBy, Closure, Expr, ExprKind, PatKind};
use rustc_lint::LateContext;
use rustc_span::sym;
use super::MAP_ERR_IGNORE;
pub(super) fn check<'tcx>(cx: &LateContext<'_>, e: &Expr<'_>, arg: &'tcx Expr<'_>) {
if let Some(method_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
&& let Some(impl_id) = cx.tcx.impl_of_method(method_id)
&& is_type_diagnostic_item(cx, cx.tcx.type_of(impl_id), sym::Result)
&& let ExprKind::Closure(&Closure {
capture_clause: CaptureBy::Ref,
body,
fn_decl_span,
..
}) = arg.kind
&& let closure_body = cx.tcx.hir().body(body)
&& let [param] = closure_body.params
&& let PatKind::Wild = param.pat.kind
{
// span the area of the closure capture and warn that the
// original error will be thrown away
span_lint_and_help(
cx,
MAP_ERR_IGNORE,
fn_decl_span,
"`map_err(|_|...` wildcard pattern discards the original error",
None,
"consider storing the original error as a source in the new error, or silence this warning using an ignored identifier (`.map_err(|_foo| ...`)",
);
}
}
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