add index checks for the slice in manual_slice_fill

Author: lapla-cogito

clippy_lints/src/loops/manual_slice_fill.rs

@@ -4,6 +4,7 @@ use clippy_utils::macros::span_is_local;
 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};
@@ -43,7 +44,10 @@ pub(super) fn check<'tcx>(
         && let ExprKind::Block(..) = body.kind
         // Check if the body is an assignment to a slice element.
         && let ExprKind::Assign(assignee, assignval, _) = peel_blocks_with_stmt(body).kind
-        && let ExprKind::Index(slice, _, _) = assignee.kind
+        && let ExprKind::Index(slice, idx, _) = assignee.kind
+        && let ExprKind::Path(Resolved(_,idx_path)) = idx.kind
+        && let Res::Local(idx_hir) = idx_path.res
+        && !is_local_used(cx, assignval, idx_hir)
         // Check if `len()` is used for the range end.
         && let ExprKind::MethodCall(path, recv,..) = end.kind
         && path.ident.name == sym::len

tests/ui/manual_slice_fill.fixed

@@ -99,3 +99,19 @@ fn should_not_lint() {
         *i = None;
     }
 }
+
+fn issue_14192() {
+    let mut tmp = [0; 3];
+
+    for i in 0..tmp.len() {
+        tmp[i] = i;
+    }
+
+    for i in 0..tmp.len() {
+        tmp[i] = 2 + i;
+    }
+
+    for i in 0..tmp.len() {
+        tmp[0] = i;
+    }
+}

tests/ui/manual_slice_fill.rs

@@ -108,3 +108,19 @@ fn should_not_lint() {
         *i = None;
     }
 }
+
+fn issue_14192() {
+    let mut tmp = vec![0; 3];
+
+    for i in 0..tmp.len() {
+        tmp[i] = i;
+    }
+
+    for i in 0..tmp.len() {
+        tmp[i] = 2 + i;
+    }
+
+    for i in 0..tmp.len() {
+        tmp[0] = i;
+    }
+}

tests/ui/manual_slice_fill.stderr

@@ -34,5 +34,14 @@ LL | |         // foo
 LL | |     }
    | |_____^ help: try: `some_slice.fill(0);`
 
-error: aborting due to 4 previous errors
+error: useless use of `vec!`
+  --> tests/ui/manual_slice_fill.rs:113:19
+   |
+LL |     let mut tmp = vec![0; 3];
+   |                   ^^^^^^^^^^ help: you can use an array directly: `[0; 3]`
+   |
+   = note: `-D clippy::useless-vec` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::useless_vec)]`
+
+error: aborting due to 5 previous errors