1 files changed, 34 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/map_err_ignore.rs b/src/tools/clippy/clippy_lints/src/methods/map_err_ignore.rs
new file mode 100644
index 000000000..1fb661714
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/map_err_ignore.rs
@@ -0,0 +1,34 @@
+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| ...`)",
+        );
+    }
+}