clippy_lints/src/methods/map_err_ignore.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::ty::is_type_diagnostic_item;
   3 use rustc_hir::{CaptureBy, Closure, Expr, ExprKind, PatKind};
   4 use rustc_lint::LateContext;
   5 use rustc_span::sym;
   6
   7 use super::MAP_ERR_IGNORE;
   8
   9 pub(super) fn check<'tcx>(cx: &LateContext<'_>, e: &Expr<'_>, arg: &'tcx Expr<'_>) {
  10     if let Some(method_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
  11         && let Some(impl_id) = cx.tcx.impl_of_method(method_id)
  12         && is_type_diagnostic_item(cx, cx.tcx.type_of(impl_id), sym::Result)
  13         && let ExprKind::Closure(&Closure {
  14             capture_clause: CaptureBy::Ref,
  15             body,
  16             fn_decl_span,
  17             ..
  18         }) = arg.kind
  19         && let closure_body = cx.tcx.hir().body(body)
  20         && let [param] = closure_body.params
  21         && let PatKind::Wild = param.pat.kind
  22     {
  23         // span the area of the closure capture and warn that the
  24         // original error will be thrown away
  25         span_lint_and_help(
  26             cx,
  27             MAP_ERR_IGNORE,
  28             fn_decl_span,
  29             "`map_err(|_|...` wildcard pattern discards the original error",
  30             None,
  31             "consider storing the original error as a source in the new error, or silence this warning using an ignored identifier (`.map_err(|_foo| ...`)",
  32         );
  33     }
  34 }