Simplify manual_memcpy suggestion in some cases

clippy_lints/src/loops.rs

@@ -950,8 +950,20 @@ fn detect_manual_memcpy<'a, 'tcx>(
  ("0", _, x, false) | (x, false, "0", false) => x.into(),
  ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
  (x, false, y, false) => format!("({} + {})", x, y),
- (x, false, y, true) => format!("({} - {})", x, y),
- (x, true, y, false) => format!("({} - {})", y, x),
+ (x, false, y, true) => {
+ if x == y {
+ "0".into()
+ } else {
+ format!("({} - {})", x, y)
+ }
+ },
+ (x, true, y, false) => {
+ if x == y {
+ "0".into()
+ } else {
+ format!("({} - {})", y, x)
+ }
+ },
  (x, true, y, true) => format!("-({} + {})", x, y),
  }
  };

tests/ui/for_loop.rs

@@ -550,6 +550,19 @@ pub fn manual_copy(src: &[i32], dst: &mut [i32], dst2: &mut [i32]) {
  for i in 0..10 {
  dst_vec[i] = src[i];
  }
+
+ // Simplify suggestion (issue #3004)
+ let src = [0, 1, 2, 3, 4];
+ let mut dst = [0, 0, 0, 0, 0, 0];
+ let from = 1;
+
+ for i in from..from + src.len() {
+ dst[i] = src[i - from];
+ }
+
+ for i in from..from + 3 {
+ dst[i] = src[i - from];
+ }
 }
 
 #[warn(clippy::needless_range_loop)]

tests/ui/for_loop.stderr

@@ -482,22 +482,34 @@ error: it looks like you're manually copying between slices
  | ^^^^^^^^^^^^^^^^ help: try replacing the loop by: `dst_vec[..src_vec.len()].clone_from_slice(&src_vec[..])`
 
 error: it looks like you're manually copying between slices
- --> $DIR/for_loop.rs:557:14
+ --> $DIR/for_loop.rs:559:14
  |
-557 | for i in 0..src.len() {
+559 | for i in from..from + src.len() {
+ | ^^^^^^^^^^^^^^^^^^^^^^ help: try replacing the loop by: `dst[from..from + src.len()].clone_from_slice(&src[0..(from + src.len() - from)])`
+
+error: it looks like you're manually copying between slices
+ --> $DIR/for_loop.rs:563:14
+ |
+563 | for i in from..from + 3 {
+ | ^^^^^^^^^^^^^^ help: try replacing the loop by: `dst[from..from + 3].clone_from_slice(&src[0..(from + 3 - from)])`
+
+error: it looks like you're manually copying between slices
+ --> $DIR/for_loop.rs:570:14
+ |
+570 | for i in 0..src.len() {
  | ^^^^^^^^^^^^ help: try replacing the loop by: `dst[..src.len()].clone_from_slice(&src[..])`
 
 error: the variable `count` is used as a loop counter. Consider using `for (count, item) in text.chars().enumerate()` or similar iterators
- --> $DIR/for_loop.rs:618:19
+ --> $DIR/for_loop.rs:631:19
  |
-618 | for ch in text.chars() {
+631 | for ch in text.chars() {
  | ^^^^^^^^^^^^
 
 error: the variable `count` is used as a loop counter. Consider using `for (count, item) in text.chars().enumerate()` or similar iterators
- --> $DIR/for_loop.rs:629:19
+ --> $DIR/for_loop.rs:642:19
  |
-629 | for ch in text.chars() {
+642 | for ch in text.chars() {
  | ^^^^^^^^^^^^
 
-error: aborting due to 61 previous errors
+error: aborting due to 63 previous errors