Handle fields on things other than self

Author: DanielEScherzer

clippy_lints/src/iter_missing_exact_size.rs

@@ -3,11 +3,12 @@ use clippy_utils::paths::{PathNS, lookup_path_str};
 use clippy_utils::sym;
 use clippy_utils::ty::{get_field_by_name, implements_trait, ty_from_hir_ty};
 use rustc_errors::MultiSpan;
-use rustc_hir::{Body, ExprKind, Impl, ImplItemKind, Item, ItemKind, OwnerId, OwnerNode};
+use rustc_hir::{Body, ExprKind, Impl, ImplItemKind, Item, ItemKind, OwnerId, OwnerNode, QPath};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::impl_lint_pass;
 use rustc_span::def_id::DefId;
 use rustc_span::sym as rustc_sym;
+use rustc_span::symbol::kw;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -151,7 +152,10 @@ impl<'tcx> LateLintPass<'tcx> for IterMissingExactSize {
             && let Some(trailing_expr) = block.expr
             && let ExprKind::MethodCall(method_name, receiver, args, _) = trailing_expr.kind
             && method_name.ident.name == sym::size_hint
-            && let ExprKind::Field(_object, field_name) = receiver.kind
+            && let ExprKind::Field(object, field_name) = receiver.kind
+            && let ExprKind::Path(QPath::Resolved(_, object_path)) = object.kind
+            && let [path_segment] = object_path.segments
+            && path_segment.ident.name == kw::SelfLower
             && args.is_empty()
         {
             // The function body is just `self.{field}.size_hint()`, check

tests/ui/iter_missing_exact_size.rs

@@ -72,6 +72,23 @@ impl Iterator for MyCollectionIter {
     }
 }
 
+// Delegates to an ExactSizeIterator but not an object field
+struct EmptyWithHint {}
+
+fn range_provider() -> (Range<usize>,) {
+    (0..5,)
+}
+
+impl Iterator for EmptyWithHint {
+    type Item = String;
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        range_provider().0.size_hint()
+    }
+}
+
 fn main() {
     let repeater = StringRepeater1 {
         original: "Foo".to_string(),
@@ -99,4 +116,7 @@ fn main() {
     for value in collection {
         println!("{value}");
     }
+
+    let mut empty_provider = EmptyWithHint {};
+    assert_eq!(None, empty_provider.next());
 }