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Auto merge of #11778 - granddaifuku:fix/reduce-indexing-manual_memcpy-when-array-length-is-equal-to-range, r=blyxyas
fix: [manual_memcpy] reduce indexing suggestions when array length is equal to loop range fixes: #11689 This PR improves `manual_memcpy` suggestions by reducing unnecessary indexing. For example, ```rust let src = [0, 1, 2, 3, 4]; let mut dest = [0; 4]; for i in 0..4 { dest[i] = src[i]; { ``` Clippy suggests `dest[..4].copy_from_slice(&src[..4]);`. I reduced this suggestion as `dest.copy_from_slice(&src[..4]);`. (Removed needless indexing.) changelog: [`manual_memcpy`]: Reduce indexing suggestions when array length is equal to loop range
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commit
ca8f33e19b
3 changed files with 90 additions and 8 deletions
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@ -178,7 +178,9 @@ fn build_manual_memcpy_suggestion<'tcx>(
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let dst_base_str = snippet(cx, dst.base.span, "???");
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let src_base_str = snippet(cx, src.base.span, "???");
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let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
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let dst = if (dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY)
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|| is_array_length_equal_to_range(cx, start, end, dst.base)
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{
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dst_base_str
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} else {
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format!("{dst_base_str}[{}..{}]", dst_offset.maybe_par(), dst_limit.maybe_par()).into()
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@ -190,11 +192,13 @@ fn build_manual_memcpy_suggestion<'tcx>(
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"clone_from_slice"
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};
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format!(
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"{dst}.{method_str}(&{src_base_str}[{}..{}]);",
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src_offset.maybe_par(),
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src_limit.maybe_par()
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)
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let src = if is_array_length_equal_to_range(cx, start, end, src.base) {
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src_base_str
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} else {
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format!("{src_base_str}[{}..{}]", src_offset.maybe_par(), src_limit.maybe_par()).into()
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};
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format!("{dst}.{method_str}(&{src});")
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}
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/// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
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@ -452,3 +456,34 @@ fn get_loop_counters<'a, 'tcx>(
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.into()
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})
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}
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fn is_array_length_equal_to_range(cx: &LateContext<'_>, start: &Expr<'_>, end: &Expr<'_>, arr: &Expr<'_>) -> bool {
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fn extract_lit_value(expr: &Expr<'_>) -> Option<u128> {
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if let ExprKind::Lit(lit) = expr.kind
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&& let ast::LitKind::Int(value, _) = lit.node
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{
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Some(value)
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} else {
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None
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}
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}
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let arr_ty = cx.typeck_results().expr_ty(arr).peel_refs();
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if let ty::Array(_, s) = arr_ty.kind() {
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let size: u128 = if let Some(size) = s.try_eval_target_usize(cx.tcx, cx.param_env) {
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size.into()
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} else {
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return false;
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};
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let range = match (extract_lit_value(start), extract_lit_value(end)) {
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(Some(start_value), Some(end_value)) => end_value - start_value,
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_ => return false,
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};
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size == range
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} else {
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false
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}
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}
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@ -138,6 +138,26 @@ pub fn manual_copy(src: &[i32], dst: &mut [i32], dst2: &mut [i32]) {
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for i in 0..dst.len() {
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dst[i] = src[i];
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}
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// Range is equal to array length
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let src = [0, 1, 2, 3, 4];
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let mut dst = [0; 4];
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for i in 0..4 {
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//~^ ERROR: it looks like you're manually copying between slices
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dst[i] = src[i];
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}
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let mut dst = [0; 6];
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for i in 0..5 {
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//~^ ERROR: it looks like you're manually copying between slices
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dst[i] = src[i];
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}
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let mut dst = [0; 5];
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for i in 0..5 {
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//~^ ERROR: it looks like you're manually copying between slices
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dst[i] = src[i];
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}
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}
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#[warn(clippy::needless_range_loop, clippy::manual_memcpy)]
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@ -106,7 +106,7 @@ LL | / for i in 0..5 {
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LL | |
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LL | | dst[i - 0] = src[i];
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LL | | }
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| |_____^ help: try replacing the loop by: `dst[..5].copy_from_slice(&src[..5]);`
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| |_____^ help: try replacing the loop by: `dst[..5].copy_from_slice(&src);`
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error: it looks like you're manually copying between slices
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--> $DIR/without_loop_counters.rs:121:5
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@ -120,11 +120,38 @@ LL | | }
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error: it looks like you're manually copying between slices
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--> $DIR/without_loop_counters.rs:145:5
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LL | / for i in 0..4 {
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LL | |
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LL | | dst[i] = src[i];
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LL | | }
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| |_____^ help: try replacing the loop by: `dst.copy_from_slice(&src[..4]);`
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error: it looks like you're manually copying between slices
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--> $DIR/without_loop_counters.rs:151:5
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LL | / for i in 0..5 {
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LL | |
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LL | | dst[i] = src[i];
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LL | | }
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| |_____^ help: try replacing the loop by: `dst[..5].copy_from_slice(&src);`
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error: it looks like you're manually copying between slices
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--> $DIR/without_loop_counters.rs:157:5
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LL | / for i in 0..5 {
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LL | |
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LL | | dst[i] = src[i];
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LL | | }
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| |_____^ help: try replacing the loop by: `dst.copy_from_slice(&src);`
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error: it looks like you're manually copying between slices
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--> $DIR/without_loop_counters.rs:165:5
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LL | / for i in 0..src.len() {
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LL | |
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LL | | dst[i] = src[i].clone();
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LL | | }
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| |_____^ help: try replacing the loop by: `dst[..src.len()].clone_from_slice(&src[..]);`
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error: aborting due to 13 previous errors
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error: aborting due to 16 previous errors
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