fix: manual_memcpy wrong indexing for multi diemnsion arrays

Author: granddaifuku

clippy_lints/src/loops/manual_memcpy.rs

@@ -59,6 +59,7 @@ pub(super) fn check<'tcx>(
                         let rhs = fetch_cloned_expr(rhs);
                         if let ExprKind::Index(base_left, idx_left, _) = lhs.kind
                             && let ExprKind::Index(base_right, idx_right, _) = rhs.kind
+                            && is_index_suggestable(base_left) && is_index_suggestable(base_right)
                             && let Some(ty) = get_slice_like_element_ty(cx, cx.typeck_results().expr_ty(base_left))
                             && get_slice_like_element_ty(cx, cx.typeck_results().expr_ty(base_right)).is_some()
                             && let Some((start_left, offset_left)) = get_details_from_idx(cx, idx_left, &starts)
@@ -486,3 +487,19 @@ fn is_array_length_equal_to_range(cx: &LateContext<'_>, start: &Expr<'_>, end: &
         false
     }
 }
+
+// Returns true if index is suggestable
+// i.e. Returns false if patterns are Index(Path(_), Path(_)) or Index(Index(_, _, _), Path(_))
+fn is_index_suggestable(expr: &Expr<'_>) -> bool {
+    if let ExprKind::Index(left_expr, right_expr, _) = expr.kind {
+        // Index(Path(_), Path(_), _) returns false
+        if matches!(left_expr.kind, ExprKind::Path(_)) {
+            return !matches!(right_expr.kind, ExprKind::Path(_));
+        }
+
+        // Nested Index pattern
+        return is_index_suggestable(left_expr) && !matches!(right_expr.kind, ExprKind::Path(_));
+    }
+
+    true
+}

tests/ui/manual_memcpy/without_loop_counters.rs

@@ -1,5 +1,5 @@
-#![warn(clippy::needless_range_loop, clippy::manual_memcpy)]
-#![allow(clippy::useless_vec)]
+#![warn(clippy::manual_memcpy)]
+#![allow(clippy::useless_vec, clippy::needless_range_loop)]
 //@no-rustfix
 const LOOP_OFFSET: usize = 5000;
 
@@ -158,6 +158,56 @@ pub fn manual_copy(src: &[i32], dst: &mut [i32], dst2: &mut [i32]) {
         //~^ ERROR: it looks like you're manually copying between slices
         dst[i] = src[i];
     }
+
+    // Don't trigger lint for following multi-dimension arrays
+    let src = [[0; 5]; 5];
+    for i in 0..5 {
+        dst[i] = src[i][i];
+    }
+    for i in 0..5 {
+        dst[i] = src[i][3];
+    }
+
+    let src = [0; 5];
+    let mut dst = [[0; 5]; 5];
+    for i in 0..5 {
+        dst[i][i] = src[i];
+    }
+
+    let src = [[[0; 5]; 5]; 5];
+    let mut dst = [0; 5];
+    for i in 0..5 {
+        dst[i] = src[i][i][i];
+    }
+    for i in 0..5 {
+        dst[i] = src[i][i][0];
+    }
+    for i in 0..5 {
+        dst[i] = src[i][0][i];
+    }
+    for i in 0..5 {
+        dst[i] = src[0][i][i];
+    }
+    for i in 0..5 {
+        dst[i] = src[0][i][1];
+    }
+    for i in 0..5 {
+        dst[i] = src[i][0][1];
+    }
+
+    // Trigger lint
+    let src = [[0; 5]; 5];
+    let mut dst = [0; 5];
+    for i in 0..5 {
+        //~^ ERROR: it looks like you're manually copying between slices
+        dst[i] = src[0][i];
+    }
+
+    let src = [[[0; 5]; 5]; 5];
+    for i in 0..5 {
+        //~^ ERROR: it looks like you're manually copying between slices
+        dst[i] = src[0][1][i];
+    }
 }
 
 #[warn(clippy::needless_range_loop, clippy::manual_memcpy)]

tests/ui/manual_memcpy/without_loop_counters.stderr

@@ -145,13 +145,31 @@ LL | |     }
    | |_____^ help: try replacing the loop by: `dst.copy_from_slice(&src);`
 
 error: it looks like you're manually copying between slices
-  --> $DIR/without_loop_counters.rs:165:5
+  --> $DIR/without_loop_counters.rs:201:5
+   |
+LL | /     for i in 0..5 {
+LL | |
+LL | |         dst[i] = src[0][i];
+LL | |     }
+   | |_____^ help: try replacing the loop by: `dst.copy_from_slice(&src[0]);`
+
+error: it looks like you're manually copying between slices
+  --> $DIR/without_loop_counters.rs:207:5
+   |
+LL | /     for i in 0..5 {
+LL | |
+LL | |         dst[i] = src[0][1][i];
+LL | |     }
+   | |_____^ help: try replacing the loop by: `dst.copy_from_slice(&src[0][1]);`
+
+error: it looks like you're manually copying between slices
+  --> $DIR/without_loop_counters.rs:215:5
    |
 LL | /     for i in 0..src.len() {
 LL | |
 LL | |         dst[i] = src[i].clone();
 LL | |     }
    | |_____^ help: try replacing the loop by: `dst[..src.len()].clone_from_slice(&src[..]);`
 
-error: aborting due to 16 previous errors
+error: aborting due to 18 previous errors