Add more tests and ignore AnonConst

Author: ebroto

clippy_lints/src/let_and_return.rs

@@ -1,8 +1,8 @@
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::{
-    AnonConst, Block, Expr, ExprKind, HirId, ImplItem, ImplItemKind, Item, ItemKind, Node, PatKind, StmtKind, TraitFn,
-    TraitItem, TraitItemKind,
+    Block, Expr, ExprKind, HirId, ImplItem, ImplItemKind, Item, ItemKind, Node, PatKind, StmtKind, TraitFn, TraitItem,
+    TraitItemKind,
 };
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
@@ -109,8 +109,8 @@ fn last_statement_borrows_locals(cx: &LateContext<'_, '_>, block: &'_ Block<'_>)
                 | Node::TraitItem(TraitItem {
                     kind: TraitItemKind::Fn(.., TraitFn::Provided(_)) | TraitItemKind::Const(.., Some(_)),
                     ..
-                })
-                | Node::AnonConst(AnonConst { .. }) => {
+                }) => {
+                    // NOTE: AnonConst is omitted because the problem can't be reproduced without implementing Drop.
                     return Some(hir_id);
                 },
                 _ => {},

tests/ui/let_return.rs

@@ -123,6 +123,33 @@ mod issue_3792 {
         let line = stdin.lock().lines().next().unwrap().unwrap();
         line
     }
+
+    // Test that it works with other fn-likes; none of these should be linted
+
+    struct S {}
+    impl S {
+        fn test() -> String {
+            let stdin = io::stdin();
+            let line = stdin.lock().lines().next().unwrap().unwrap();
+            line
+        }
+    }
+
+    trait T {
+        fn test() -> String {
+            let stdin = io::stdin();
+            let line = stdin.lock().lines().next().unwrap().unwrap();
+            line
+        }
+    }
+
+    fn in_closure() {
+        let _ = || {
+            let stdin = io::stdin();
+            let line = stdin.lock().lines().next().unwrap().unwrap();
+            line
+        };
+    }
 }
 
 fn main() {}