Fix while_let_on_iterator

When the iterator is one field within a local correctly check for usages of the field

clippy_lints/src/loops/while_let_on_iterator.rs

@@ -146,7 +146,7 @@ fn is_expr_same_child_or_parent_field(cx: &LateContext<'_>, expr: &Expr<'_>, fie
     match expr.kind {
         ExprKind::Field(base, name) => {
             if let Some((head_field, tail_fields)) = fields.split_first() {
-                if name.name == *head_field && is_expr_same_field(cx, base, fields, path_res) {
+                if name.name == *head_field && is_expr_same_field(cx, base, tail_fields, path_res) {
                     return true;
                 }
                 // Check if the expression is a parent field

tests/ui/while_let_on_iterator.fixed

@@ -357,6 +357,15 @@ fn issue7510() {
     println!("{}", it.0.next().unwrap());
 }
 
+fn exact_match_with_single_field() {
+    struct S<T>(T);
+    let mut s = S(0..10);
+    // Don't lint. `s.0` is used inside the loop.
+    while let Some(_) = s.0.next() {
+        let _ = &mut s.0;
+    }
+}
+
 fn main() {
     let mut it = 0..20;
     for _ in it {

tests/ui/while_let_on_iterator.rs

@@ -357,6 +357,15 @@ fn issue7510() {
     println!("{}", it.0.next().unwrap());
 }
 
+fn exact_match_with_single_field() {
+    struct S<T>(T);
+    let mut s = S(0..10);
+    // Don't lint. `s.0` is used inside the loop.
+    while let Some(_) = s.0.next() {
+        let _ = &mut s.0;
+    }
+}
+
 fn main() {
     let mut it = 0..20;
     while let Some(..) = it.next() {

tests/ui/while_let_on_iterator.stderr

@@ -123,7 +123,7 @@ LL |     while let Some(x) = it.0.next() {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in &mut *it.0`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_let_on_iterator.rs:362:5
+  --> $DIR/while_let_on_iterator.rs:371:5
    |
 LL |     while let Some(..) = it.next() {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for _ in it`