len_without_is_empty will now consider multiple impl blocks

`len_without_is_empty` will now consider `#[allow]` on both the `len` method, and the type definition

clippy_utils/src/lib.rs

@@ -63,9 +63,9 @@ use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_hir::Node;
 use rustc_hir::{
-    def, Arm, Block, Body, Constness, Crate, Expr, ExprKind, FnDecl, GenericArgs, HirId, ImplItem, ImplItemKind, Item,
-    ItemKind, MatchSource, Param, Pat, PatKind, Path, PathSegment, QPath, TraitItem, TraitItemKind, TraitRef, TyKind,
-    Unsafety,
+    def, Arm, Block, Body, Constness, Crate, Expr, ExprKind, FnDecl, GenericArgs, HirId, Impl, ImplItem, ImplItemKind,
+    Item, ItemKind, MatchSource, Param, Pat, PatKind, Path, PathSegment, QPath, TraitItem, TraitItemKind, TraitRef,
+    TyKind, Unsafety,
 };
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::{LateContext, Level, Lint, LintContext};
@@ -1004,6 +1004,21 @@ pub fn get_enclosing_block<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Optio
     })
 }
 
+/// Gets the parent node if it's an impl block.
+pub fn get_parent_as_impl(tcx: TyCtxt<'_>, id: HirId) -> Option<&Impl<'_>> {
+    let map = tcx.hir();
+    match map.parent_iter(id).next() {
+        Some((
+            _,
+            Node::Item(Item {
+                kind: ItemKind::Impl(imp),
+                ..
+            }),
+        )) => Some(imp),
+        _ => None,
+    }
+}
+
 /// Returns the base type for HIR references and pointers.
 pub fn walk_ptrs_hir_ty<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
     match ty.kind {