Fix #2496

clippy_lints/src/loops.rs

@@ -1624,7 +1624,8 @@ impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
         if_chain! {
             // a range index op
             if let ExprMethodCall(ref meth, _, ref args) = expr.node;
-            if meth.name == "index" || meth.name == "index_mut";
+            if (meth.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
+                || (meth.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
             if !self.check(&args[1], &args[0], expr);
             then { return }
         }

clippy_lints/src/utils/paths.rs

@@ -33,6 +33,8 @@ pub const HASH: [&str; 2] = ["hash", "Hash"];
 pub const HASHMAP: [&str; 5] = ["std", "collections", "hash", "map", "HashMap"];
 pub const HASHMAP_ENTRY: [&str; 5] = ["std", "collections", "hash", "map", "Entry"];
 pub const HASHSET: [&str; 5] = ["std", "collections", "hash", "set", "HashSet"];
+pub const INDEX: [&str; 3] = ["core", "ops", "Index"];
+pub const INDEX_MUT: [&str; 3] = ["core", "ops", "IndexMut"];
 pub const INIT: [&str; 4] = ["core", "intrinsics", "", "init"];
 pub const INTO: [&str; 3] = ["core", "convert", "Into"];
 pub const INTO_ITERATOR: [&str; 4] = ["core", "iter", "traits", "IntoIterator"];

tests/ui/for_loop.rs

@@ -556,3 +556,18 @@ pub fn manual_copy_same_destination(dst: &mut [i32], d: usize, s: usize) {
         dst[d + i] = dst[s + i];
     }
 }
+
+mod issue_2496 {
+    pub trait Handle {
+        fn new_for_index(index: usize) -> Self;
+        fn index(&self) -> usize;
+    }
+
+    pub fn test<H: Handle>() -> H {
+        for x in 0..5 {
+            let next_handle = H::new_for_index(x);
+            println!("{}", next_handle.index());
+        }
+        unimplemented!()
+    }
+}