manual_slice_fill: initializer must not reference the iterator

```rust
let mut tmp = vec![1, 2, 3];
for b in &mut tmp {
    *b = !*b;
}
```

must not suggest the invalid `tmp.fill(!*b)`.

Author: samueltardieu

clippy_lints/src/loops/manual_slice_fill.rs

@@ -1,9 +1,12 @@
+use std::ops::ControlFlow;
+
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::eager_or_lazy::switch_to_eager_eval;
 use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::{HasSession, snippet_with_applicability};
 use clippy_utils::ty::implements_trait;
-use clippy_utils::{higher, peel_blocks_with_stmt, span_contains_comment};
+use clippy_utils::visitors::for_each_expr;
+use clippy_utils::{higher, path_to_local_id, peel_blocks_with_stmt, span_contains_comment};
 use rustc_ast::ast::LitKind;
 use rustc_ast::{RangeLimits, UnOp};
 use rustc_data_structures::packed::Pu128;
@@ -71,6 +74,10 @@ pub(super) fn check<'tcx>(
         && local == pat.hir_id
         && !assignval.span.from_expansion()
         && switch_to_eager_eval(cx, assignval)
+        // `assignval` must not reference the iterator
+        && for_each_expr(cx, assignval, |e|
+            if path_to_local_id(e, local) { ControlFlow::Break(()) } else { ControlFlow::Continue(()) }
+        ).is_none()
         // The `fill` method cannot be used if the slice's element type does not implement the `Clone` trait.
         && let Some(clone_trait) = cx.tcx.lang_items().clone_trait()
         && implements_trait(cx, cx.typeck_results().expr_ty(recv), clone_trait, &[])

tests/ui/manual_slice_fill.fixed

@@ -99,3 +99,11 @@ fn should_not_lint() {
         *i = None;
     }
 }
+
+fn issue14189() {
+    // Should not lint because `!*b` is not constant
+    let mut tmp = vec![1, 2, 3];
+    for b in &mut tmp {
+        *b = !*b;
+    }
+}

tests/ui/manual_slice_fill.rs

@@ -108,3 +108,11 @@ fn should_not_lint() {
         *i = None;
     }
 }
+
+fn issue14189() {
+    // Should not lint because `!*b` is not constant
+    let mut tmp = vec![1, 2, 3];
+    for b in &mut tmp {
+        *b = !*b;
+    }
+}