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

@@ -3,6 +3,7 @@ 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::visitors::is_local_used;
 use clippy_utils::{higher, peel_blocks_with_stmt, span_contains_comment};
 use rustc_ast::ast::LitKind;
 use rustc_ast::{RangeLimits, UnOp};
@@ -71,6 +72,8 @@ 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
+        && !is_local_used(cx, assignval, local)
         // 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;
+    }
+}