Reduce false-positives for needless_pass_by_value lint
Excluding a type whose reference also fulfills the trait bound.
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sinkuu
parent
12a7d1489a
commit
bf97cd0338
3 changed files with 108 additions and 77 deletions
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@ -1,7 +1,7 @@
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use rustc::hir::*;
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use rustc::hir::intravisit::FnKind;
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use rustc::lint::*;
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use rustc::ty::{self, TypeFoldable};
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use rustc::ty::{self, RegionKind, TypeFoldable};
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use rustc::traits;
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use rustc::middle::expr_use_visitor as euv;
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use rustc::middle::mem_categorization as mc;
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@ -73,18 +73,25 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
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_ => return,
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}
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// Allows these to be passed by value.
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let fn_trait = need!(cx.tcx.lang_items().fn_trait());
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let asref_trait = need!(get_trait_def_id(cx, &paths::ASREF_TRAIT));
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let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
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let fn_trait = need!(cx.tcx.lang_items().fn_trait());
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let sized_trait = need!(cx.tcx.lang_items().sized_trait());
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let fn_def_id = cx.tcx.hir.local_def_id(node_id);
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let preds: Vec<ty::Predicate> = {
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traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
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.filter(|p| !p.is_global())
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.collect()
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};
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let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
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.filter(|p| !p.is_global())
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.collect::<Vec<_>>();
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let preds = preds
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.iter()
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.filter_map(|pred| if let ty::Predicate::Trait(ref poly_trait_ref) = *pred {
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Some(poly_trait_ref.skip_binder())
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} else {
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None
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})
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.filter(|t| t.def_id() != sized_trait && !t.has_escaping_regions())
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.collect::<Vec<_>>();
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// Collect moved variables and spans which will need dereferencings from the
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// function body.
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@ -103,40 +110,44 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
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let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);
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for ((input, &ty), arg) in decl.inputs.iter().zip(fn_sig.inputs()).zip(&body.arguments) {
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// Determines whether `ty` implements `Borrow<U>` (U != ty) specifically.
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// This is needed due to the `Borrow<T> for T` blanket impl.
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let implements_borrow_trait = preds
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.iter()
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.filter_map(|pred| if let ty::Predicate::Trait(ref poly_trait_ref) = *pred {
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Some(poly_trait_ref.skip_binder())
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} else {
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None
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})
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.filter(|tpred| tpred.def_id() == borrow_trait && tpred.self_ty() == ty)
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.any(|tpred| {
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tpred
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.input_types()
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.nth(1)
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.expect("Borrow trait must have an parameter") != ty
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});
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// * Exclude a type that is specifically bounded by `Borrow`.
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// * Exclude a type whose reference also fulfills its bound.
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// (e.g. `std::borrow::Borrow`, `serde::Serialize`)
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let (implements_borrow_trait, all_borrowable_trait) = {
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let preds = preds
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.iter()
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.filter(|t| t.self_ty() == ty)
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.collect::<Vec<_>>();
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(
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preds.iter().any(|t| t.def_id() == borrow_trait),
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!preds.is_empty() && preds.iter().all(|t| {
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implements_trait(
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cx,
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cx.tcx.mk_imm_ref(&RegionKind::ReErased, ty),
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t.def_id(),
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&t.input_types().skip(1).collect::<Vec<_>>(),
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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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!is_self(arg),
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!ty.is_mutable_pointer(),
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!is_copy(cx, ty),
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!implements_trait(cx, ty, fn_trait, &[]),
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!implements_trait(cx, ty, asref_trait, &[]),
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!implements_borrow_trait,
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!all_borrowable_trait,
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let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node,
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!moved_vars.contains(&canonical_id),
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], {
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// Note: `toplevel_ref_arg` warns if `BindByRef`
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if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut {
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continue;
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}
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// Suggestion logic
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// Dereference suggestion
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let sugg = |db: &mut DiagnosticBuilder| {
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let deref_span = spans_need_deref.get(&canonical_id);
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if_let_chain! {[
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@ -152,33 +163,37 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
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"consider changing the type to",
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slice_ty);
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assert!(deref_span.is_none());
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return; // `Vec` and `String` cannot be destructured - no need for `*` suggestion
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return; // `Vec` cannot be destructured - no need for `*` suggestion
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}}
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if match_type(cx, ty, &paths::STRING) {
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db.span_suggestion(input.span,
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"consider changing the type to",
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"&str".to_string());
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db.span_suggestion(input.span, "consider changing the type to", "&str".to_string());
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assert!(deref_span.is_none());
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return;
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return; // ditto
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}
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let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
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// Suggests adding `*` to dereference the added reference.
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if let Some(deref_span) = deref_span {
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spans.extend(deref_span.iter().cloned()
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.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))));
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spans.extend(
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deref_span
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.iter()
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.cloned()
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.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))),
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);
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spans.sort_by_key(|&(span, _)| span);
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}
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multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
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};
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span_lint_and_then(cx,
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NEEDLESS_PASS_BY_VALUE,
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input.span,
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"this argument is passed by value, but not consumed in the function body",
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sugg);
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span_lint_and_then(
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cx,
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NEEDLESS_PASS_BY_VALUE,
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input.span,
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"this argument is passed by value, but not consumed in the function body",
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sugg,
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);
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}}
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}
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}
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@ -188,8 +203,7 @@ struct MovedVariablesCtxt<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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moved_vars: HashSet<NodeId>,
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/// Spans which need to be prefixed with `*` for dereferencing the
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/// suggested additional
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/// reference.
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/// suggested additional reference.
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spans_need_deref: HashMap<NodeId, HashSet<Span>>,
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}
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@ -213,9 +227,7 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
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fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: mc::cmt<'tcx>) {
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let cmt = unwrap_downcast_or_interior(cmt);
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if_let_chain! {[
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let mc::Categorization::Local(vid) = cmt.cat,
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], {
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if let mc::Categorization::Local(vid) = cmt.cat {
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let mut id = matched_pat.id;
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loop {
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let parent = self.cx.tcx.hir.get_parent_node(id);
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@ -235,7 +247,7 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
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.or_insert_with(HashSet::new)
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.insert(c.span);
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}
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}
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},
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map::Node::NodeStmt(s) => {
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// `let <pat> = x;`
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@ -251,13 +263,13 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
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.map(|e| e.span)
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.expect("`let` stmt without init aren't caught by match_pat"));
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}}
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}
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},
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_ => {}
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_ => {},
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}
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}
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}
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}}
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}
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}
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}
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@ -4,6 +4,9 @@
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#![warn(needless_pass_by_value)]
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#![allow(dead_code, single_match, if_let_redundant_pattern_matching, many_single_char_names)]
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use std::borrow::Borrow;
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use std::convert::AsRef;
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// `v` should be warned
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// `w`, `x` and `y` are allowed (moved or mutated)
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fn foo<T: Default>(v: Vec<T>, w: Vec<T>, mut x: Vec<T>, y: Vec<T>) -> Vec<T> {
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@ -25,10 +28,11 @@ fn bar(x: String, y: Wrapper) {
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assert_eq!(y.0.len(), 42);
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}
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// U implements `Borrow<U>`, but should be warned correctly
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fn test_borrow_trait<T: std::borrow::Borrow<str>, U>(t: T, u: U) {
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// V implements `Borrow<V>`, but should be warned correctly
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fn test_borrow_trait<T: Borrow<str>, U: AsRef<str>, V>(t: T, u: U, v: V) {
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println!("{}", t.borrow());
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consume(&u);
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println!("{}", u.as_ref());
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consume(&v);
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}
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// ok
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@ -59,4 +63,13 @@ fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
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println!("{}", t);
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}
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trait Foo {}
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// `S: Serialize` can be passed by value
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trait Serialize {}
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impl<'a, T> Serialize for &'a T where T: Serialize {}
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impl Serialize for i32 {}
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fn test_blanket_ref<T: Foo, S: Serialize>(_foo: T, _serializable: S) {}
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fn main() {}
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@ -1,58 +1,64 @@
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:9:23
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9 | fn foo<T: Default>(v: Vec<T>, w: Vec<T>, mut x: Vec<T>, y: Vec<T>) -> Vec<T> {
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| ^^^^^^ help: consider changing the type to: `&[T]`
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= note: `-D needless-pass-by-value` implied by `-D warnings`
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--> $DIR/needless_pass_by_value.rs:12:23
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12 | fn foo<T: Default>(v: Vec<T>, w: Vec<T>, mut x: Vec<T>, y: Vec<T>) -> Vec<T> {
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| ^^^^^^ help: consider changing the type to: `&[T]`
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= note: `-D needless-pass-by-value` implied by `-D warnings`
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:23:11
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--> $DIR/needless_pass_by_value.rs:26:11
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23 | fn bar(x: String, y: Wrapper) {
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26 | fn bar(x: String, y: Wrapper) {
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| ^^^^^^ help: consider changing the type to: `&str`
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:23:22
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--> $DIR/needless_pass_by_value.rs:26:22
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23 | fn bar(x: String, y: Wrapper) {
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26 | fn bar(x: String, y: Wrapper) {
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| ^^^^^^^ help: consider taking a reference instead: `&Wrapper`
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:29:63
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--> $DIR/needless_pass_by_value.rs:32:71
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29 | fn test_borrow_trait<T: std::borrow::Borrow<str>, U>(t: T, u: U) {
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| ^ help: consider taking a reference instead: `&U`
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32 | fn test_borrow_trait<T: Borrow<str>, U: AsRef<str>, V>(t: T, u: U, v: V) {
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| ^ help: consider taking a reference instead: `&V`
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:40:18
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--> $DIR/needless_pass_by_value.rs:44:18
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40 | fn test_match(x: Option<Option<String>>, y: Option<Option<String>>) {
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44 | fn test_match(x: Option<Option<String>>, y: Option<Option<String>>) {
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| ^^^^^^^^^^^^^^^^^^^^^^
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help: consider taking a reference instead
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40 | fn test_match(x: &Option<Option<String>>, y: Option<Option<String>>) {
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41 | match *x {
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44 | fn test_match(x: &Option<Option<String>>, y: Option<Option<String>>) {
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45 | match *x {
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:53:24
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--> $DIR/needless_pass_by_value.rs:57:24
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53 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
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57 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
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| ^^^^^^^ help: consider taking a reference instead: `&Wrapper`
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:53:36
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--> $DIR/needless_pass_by_value.rs:57:36
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53 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
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57 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
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| ^^^^^^^
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help: consider taking a reference instead
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53 | fn test_destructure(x: Wrapper, y: &Wrapper, z: Wrapper) {
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54 | let Wrapper(s) = z; // moved
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55 | let Wrapper(ref t) = *y; // not moved
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56 | let Wrapper(_) = *y; // still not moved
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57 | fn test_destructure(x: Wrapper, y: &Wrapper, z: Wrapper) {
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58 | let Wrapper(s) = z; // moved
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59 | let Wrapper(ref t) = *y; // not moved
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60 | let Wrapper(_) = *y; // still not moved
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error: this argument is passed by value, but not consumed in the function body
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--> $DIR/needless_pass_by_value.rs:73:49
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73 | fn test_blanket_ref<T: Foo, S: Serialize>(_foo: T, _serializable: S) {}
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| ^ help: consider taking a reference instead: `&T`
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