mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-11-23 21:23:56 +00:00
Add lint to detect manual slice copies
This commit is contained in:
Marcus Klaas
Oliver Schneider
parent
b32631794a
commit
90f345df94
2 changed files with 368 additions and 57 deletions
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@ -1,3 +1,4 @@
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use itertools::Itertools;
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use reexport::*;
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use rustc::hir::*;
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use rustc::hir::def::Def;
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@ -15,10 +16,29 @@ use syntax::ast;
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use utils::sugg;
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use utils::{get_enclosing_block, get_parent_expr, higher, in_external_macro, is_integer_literal, is_refutable,
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last_path_segment, match_trait_method, match_type, multispan_sugg, snippet, span_help_and_lint, span_lint,
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span_lint_and_sugg, span_lint_and_then};
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last_path_segment, match_trait_method, match_type, multispan_sugg, snippet, snippet_opt,
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span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then};
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use utils::paths;
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/// **What it does:** Checks for for loops that manually copy items between
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/// slices that could be optimized by having a memcpy.
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///
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/// **Why is this bad?** It is not as fast as a memcpy.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// for i in 0..src.len() {
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/// dst[i + 64] = src[i];
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/// }
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/// ```
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declare_lint! {
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pub MANUAL_MEMCPY,
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Warn,
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"manually copying items between slices"
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}
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/// **What it does:** Checks for looping over the range of `0..len` of some
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/// collection just to get the values by index.
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///
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@ -314,6 +334,7 @@ pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(
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MANUAL_MEMCPY,
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NEEDLESS_RANGE_LOOP,
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EXPLICIT_ITER_LOOP,
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EXPLICIT_INTO_ITER_LOOP,
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@ -570,6 +591,249 @@ fn check_for_loop<'a, 'tcx>(
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check_for_loop_arg(cx, pat, arg, expr);
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check_for_loop_explicit_counter(cx, arg, body, expr);
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check_for_loop_over_map_kv(cx, pat, arg, body, expr);
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detect_manual_memcpy(cx, pat, arg, body, expr);
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}
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fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: DefId) -> bool {
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if_let_chain! {[
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let ExprPath(ref qpath) = expr.node,
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let QPath::Resolved(None, ref path) = *qpath,
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path.segments.len() == 1,
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// our variable!
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cx.tables.qpath_def(qpath, expr.hir_id).def_id() == var
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], {
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return true;
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}}
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false
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}
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struct Offset {
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value: String,
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negate: bool,
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}
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impl Offset {
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fn negative(s: String) -> Self {
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Self {
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value: s,
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negate: true,
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}
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}
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fn positive(s: String) -> Self {
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Self {
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value: s,
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negate: false,
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}
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}
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}
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struct FixedOffsetVar {
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var_name: String,
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offset: Offset,
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}
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fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty) -> bool {
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let is_slice = match ty.sty {
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ty::TyRef(_, ref subty) => is_slice_like(cx, subty.ty),
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ty::TySlice(..) | ty::TyArray(..) => true,
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_ => false,
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};
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is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
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}
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fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: DefId) -> Option<FixedOffsetVar> {
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fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: DefId) -> Option<String> {
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match e.node {
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ExprLit(ref l) => match l.node {
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ast::LitKind::Int(x, _ty) => Some(x.to_string()),
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_ => None,
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},
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ExprPath(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
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_ => None,
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}
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}
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if let ExprIndex(ref seqexpr, ref idx) = expr.node {
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let ty = cx.tables.expr_ty(seqexpr);
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if !is_slice_like(cx, ty) {
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return None;
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}
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let offset = match idx.node {
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ExprBinary(op, ref lhs, ref rhs) => match op.node {
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BinOp_::BiAdd => {
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let offset_opt = if same_var(cx, lhs, var) {
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extract_offset(cx, rhs, var)
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} else if same_var(cx, rhs, var) {
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extract_offset(cx, lhs, var)
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} else {
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None
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};
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offset_opt.map(Offset::positive)
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},
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BinOp_::BiSub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
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_ => None,
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},
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ExprPath(..) => if same_var(cx, idx, var) {
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Some(Offset::positive("0".into()))
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} else {
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None
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},
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_ => None,
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};
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offset.map(|o| {
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FixedOffsetVar {
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var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
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offset: o,
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}
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})
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} else {
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None
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}
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}
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fn get_indexed_assignments<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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body: &Expr,
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var: DefId,
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) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
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fn get_assignment<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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e: &Expr,
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var: DefId,
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) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
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if let Expr_::ExprAssign(ref lhs, ref rhs) = e.node {
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match (get_fixed_offset_var(cx, lhs, var), get_fixed_offset_var(cx, rhs, var)) {
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(Some(offset_left), Some(offset_right)) => Some((offset_left, offset_right)),
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_ => None,
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}
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} else {
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None
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}
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}
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if let Expr_::ExprBlock(ref b) = body.node {
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let Block {
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ref stmts,
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ref expr,
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..
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} = **b;
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stmts
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.iter()
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.map(|stmt| match stmt.node {
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Stmt_::StmtDecl(..) => None,
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Stmt_::StmtExpr(ref e, _node_id) | Stmt_::StmtSemi(ref e, _node_id) => Some(get_assignment(cx, e, var)),
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})
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.chain(
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expr.as_ref()
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.into_iter()
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.map(|e| Some(get_assignment(cx, &*e, var))),
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)
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.filter_map(|op| op)
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.collect::<Option<Vec<_>>>()
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.unwrap_or_else(|| vec![])
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} else {
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get_assignment(cx, body, var).into_iter().collect()
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}
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}
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/// Check for for loops that sequentially copy items from one slice-like
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/// object to another.
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fn detect_manual_memcpy<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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pat: &'tcx Pat,
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arg: &'tcx Expr,
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body: &'tcx Expr,
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expr: &'tcx Expr,
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) {
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if let Some(higher::Range {
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start: Some(start),
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ref end,
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limits,
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}) = higher::range(arg)
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{
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// the var must be a single name
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if let PatKind::Binding(_, def_id, _, _) = pat.node {
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let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
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match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
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("0", _, "0", _) => "".into(),
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("0", _, x, false) | (x, false, "0", false) => x.into(),
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("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
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(x, false, y, false) => format!("({} + {})", x, y),
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(x, false, y, true) => format!("({} - {})", x, y),
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(x, true, y, false) => format!("({} - {})", y, x),
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(x, true, y, true) => format!("-({} + {})", x, y),
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}
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};
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let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| if let Some(end) = *end {
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if_let_chain! {[
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let ExprMethodCall(ref method, _, ref len_args) = end.node,
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method.name == "len",
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len_args.len() == 1,
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let Some(arg) = len_args.get(0),
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snippet(cx, arg.span, "??") == var_name,
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], {
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return if offset.negate {
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format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
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} else {
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"".to_owned()
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};
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}}
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let end_str = match limits {
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ast::RangeLimits::Closed => {
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let end = sugg::Sugg::hir(cx, end, "<count>");
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format!("{}", end + sugg::ONE)
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},
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ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
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};
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print_sum(&Offset::positive(end_str), &offset)
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} else {
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"..".into()
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};
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// The only statements in the for loops can be indexed assignments from
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// indexed retrievals.
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let manual_copies = get_indexed_assignments(cx, body, def_id);
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let big_sugg = manual_copies
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.into_iter()
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.map(|(dst_var, src_var)| {
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let start_str = Offset::positive(snippet_opt(cx, start.span).unwrap_or_else(|| "".into()));
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let dst_offset = print_sum(&start_str, &dst_var.offset);
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let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
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let src_offset = print_sum(&start_str, &src_var.offset);
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let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
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let dst = if dst_offset == "" && dst_limit == "" {
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dst_var.var_name
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} else {
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format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
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};
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format!("{}.clone_from_slice(&{}[{}..{}])", dst, src_var.var_name, src_offset, src_limit)
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})
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.join("\n ");
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if !big_sugg.is_empty() {
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span_lint_and_sugg(
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cx,
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MANUAL_MEMCPY,
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expr.span,
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"it looks like you're manually copying between slices",
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"try replacing the loop by",
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big_sugg,
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);
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}
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}
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}
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}
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/// Check for looping over a range and then indexing a sequence with it.
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@ -1024,9 +1288,29 @@ impl<'tcx> Visitor<'tcx> for UsedVisitor {
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fn visit_expr(&mut self, expr: &'tcx Expr) {
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if match_var(expr, self.var) {
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self.used = true;
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return;
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} else {
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walk_expr(self, expr);
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}
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}
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fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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NestedVisitorMap::None
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}
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}
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struct DefIdUsedVisitor<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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def_id: DefId,
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used: bool,
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}
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impl<'a, 'tcx: 'a> Visitor<'tcx> for DefIdUsedVisitor<'a, 'tcx> {
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fn visit_expr(&mut self, expr: &'tcx Expr) {
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if same_var(self.cx, expr, self.def_id) {
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self.used = true;
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} else {
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walk_expr(self, expr);
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}
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walk_expr(self, expr);
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}
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fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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@ -1054,40 +1338,46 @@ impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
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if_let_chain! {[
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// an index op
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let ExprIndex(ref seqexpr, ref idx) = expr.node,
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// directly indexing a variable
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let ExprPath(ref qpath) = idx.node,
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let QPath::Resolved(None, ref path) = *qpath,
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path.segments.len() == 1,
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// our variable!
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self.cx.tables.qpath_def(qpath, expr.hir_id).def_id() == self.var,
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// the indexed container is referenced by a name
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let ExprPath(ref seqpath) = seqexpr.node,
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let QPath::Resolved(None, ref seqvar) = *seqpath,
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seqvar.segments.len() == 1,
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], {
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let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
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match def {
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Def::Local(..) | Def::Upvar(..) => {
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let def_id = def.def_id();
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let node_id = self.cx.tcx.hir.as_local_node_id(def_id).expect("local/upvar are local nodes");
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let hir_id = self.cx.tcx.hir.node_to_hir_id(node_id);
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let index_used = same_var(self.cx, idx, self.var) || {
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let mut used_visitor = DefIdUsedVisitor {
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cx: self.cx,
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def_id: self.var,
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used: false,
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};
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walk_expr(&mut used_visitor, idx);
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used_visitor.used
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};
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let parent_id = self.cx.tcx.hir.get_parent(expr.id);
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let parent_def_id = self.cx.tcx.hir.local_def_id(parent_id);
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let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
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self.indexed.insert(seqvar.segments[0].name, Some(extent));
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return; // no need to walk further
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if index_used {
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let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
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match def {
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Def::Local(..) | Def::Upvar(..) => {
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let def_id = def.def_id();
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let node_id = self.cx.tcx.hir.as_local_node_id(def_id).expect("local/upvar are local nodes");
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let hir_id = self.cx.tcx.hir.node_to_hir_id(node_id);
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let parent_id = self.cx.tcx.hir.get_parent(expr.id);
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let parent_def_id = self.cx.tcx.hir.local_def_id(parent_id);
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let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
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self.indexed.insert(seqvar.segments[0].name, Some(extent));
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return; // no need to walk further *on the variable*
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}
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Def::Static(..) | Def::Const(..) => {
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self.indexed.insert(seqvar.segments[0].name, None);
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return; // no need to walk further *on the variable*
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}
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_ => (),
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}
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Def::Static(..) | Def::Const(..) => {
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self.indexed.insert(seqvar.segments[0].name, None);
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return; // no need to walk further
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}
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_ => (),
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}
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}}
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|
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if_let_chain! {[
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// directly indexing a variable
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// directly using a variable
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let ExprPath(ref qpath) = expr.node,
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let QPath::Resolved(None, ref path) = *qpath,
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path.segments.len() == 1,
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|
|
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|
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@ -505,57 +505,78 @@ help: use the corresponding method
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409 | for k in rm.keys() {
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| ^
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error: the loop variable `i` is used to index `src`
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error: it looks like you're manually copying between slices
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--> $DIR/for_loop.rs:462:5
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|
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462 | / for i in 0..src.len() {
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463 | | dst[i] = src[i];
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464 | | }
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| |_____^ help: try replacing the loop by: `dst[..src.len()].clone_from_slice(&src[..])`
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|
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= note: `-D manual-memcpy` implied by `-D warnings`
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error: it looks like you're manually copying between slices
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--> $DIR/for_loop.rs:467:5
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|
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467 | / for i in 0..src.len() {
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468 | | dst[i + 10] = src[i];
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469 | | }
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| |_____^
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|
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help: consider using an iterator
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|
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467 | for (i, <item>) in src.iter().enumerate() {
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| ^^^^^^^^^^^
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| |_____^ help: try replacing the loop by: `dst[10..(src.len() + 10)].clone_from_slice(&src[..])`
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error: the loop variable `i` is used to index `dst`
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error: it looks like you're manually copying between slices
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--> $DIR/for_loop.rs:472:5
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|
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472 | / for i in 0..src.len() {
|
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473 | | dst[i] = src[i + 10];
|
||||
474 | | }
|
||||
| |_____^
|
||||
|
|
||||
help: consider using an iterator
|
||||
|
|
||||
472 | for (i, <item>) in dst.iter().enumerate().take(src.len()) {
|
||||
| ^^^^^^^^^^^
|
||||
| |_____^ help: try replacing the loop by: `dst[..src.len()].clone_from_slice(&src[10..])`
|
||||
|
||||
error: the loop variable `i` is used to index `dst`
|
||||
error: it looks like you're manually copying between slices
|
||||
--> $DIR/for_loop.rs:477:5
|
||||
|
|
||||
477 | / for i in 11..src.len() {
|
||||
478 | | dst[i] = src[i - 10];
|
||||
479 | | }
|
||||
| |_____^ help: try replacing the loop by: `dst[11..src.len()].clone_from_slice(&src[(11 - 10)..(src.len() - 10)])`
|
||||
|
||||
error: it looks like you're manually copying between slices
|
||||
--> $DIR/for_loop.rs:482:5
|
||||
|
|
||||
482 | / for i in 0..dst.len() {
|
||||
483 | | dst[i] = src[i];
|
||||
484 | | }
|
||||
| |_____^ help: try replacing the loop by: `dst.clone_from_slice(&src[..dst.len()])`
|
||||
|
||||
error: it looks like you're manually copying between slices
|
||||
--> $DIR/for_loop.rs:495:5
|
||||
|
|
||||
495 | / for i in 10..256 {
|
||||
496 | | dst[i] = src[i - 5];
|
||||
497 | | dst2[i + 500] = src[i]
|
||||
498 | | }
|
||||
| |_____^
|
||||
|
|
||||
help: consider using an iterator
|
||||
help: try replacing the loop by
|
||||
|
|
||||
495 | dst[10..256].clone_from_slice(&src[(10 - 5)..(256 - 5)])
|
||||
496 | dst2[(10 + 500)..(256 + 500)].clone_from_slice(&src[10..256])
|
||||
|
|
||||
477 | for (i, <item>) in dst.iter().enumerate().take(src.len()).skip(11) {
|
||||
| ^^^^^^^^^^^
|
||||
|
||||
error: the loop variable `i` is used to index `src`
|
||||
--> $DIR/for_loop.rs:512:5
|
||||
error: it looks like you're manually copying between slices
|
||||
--> $DIR/for_loop.rs:507:5
|
||||
|
|
||||
512 | / for i in 0..10 {
|
||||
513 | | dst[i + i] = src[i];
|
||||
514 | | }
|
||||
| |_____^
|
||||
|
|
||||
help: consider using an iterator
|
||||
|
|
||||
512 | for (i, <item>) in src.iter().enumerate().take(10) {
|
||||
| ^^^^^^^^^^^
|
||||
507 | / for i in 10..LOOP_OFFSET {
|
||||
508 | | dst[i + LOOP_OFFSET] = src[i - some_var];
|
||||
509 | | }
|
||||
| |_____^ help: try replacing the loop by: `dst[(10 + LOOP_OFFSET)..(LOOP_OFFSET + LOOP_OFFSET)].clone_from_slice(&src[(10 - some_var)..(LOOP_OFFSET - some_var)])`
|
||||
|
||||
error: aborting due to 54 previous errors
|
||||
error: it looks like you're manually copying between slices
|
||||
--> $DIR/for_loop.rs:520:5
|
||||
|
|
||||
520 | / for i in 0..src_vec.len() {
|
||||
521 | | dst_vec[i] = src_vec[i];
|
||||
522 | | }
|
||||
| |_____^ help: try replacing the loop by: `dst_vec[..src_vec.len()].clone_from_slice(&src_vec[..])`
|
||||
|
||||
error: aborting due to 58 previous errors
|
||||
|
||||
|
|
|
|||
Loading…
Reference in a new issue