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Reduce false-positives for needless_pass_by_value lint

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Excluding a type whose reference also fulfills the trait bound.
This commit is contained in:
sinkuu
2017-10-08 10:23:41 +09:00
parent 12a7d1489a
commit bf97cd0338
3 changed files with 108 additions and 77 deletions
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110
clippy_lints/src/needless_pass_by_value.rs
View File

@@ -1,7 +1,7 @@
use rustc::hir::*;
use rustc::hir::intravisit::FnKind;
use rustc::lint::*;
use rustc::ty::{self, TypeFoldable};
use rustc::ty::{self, RegionKind, TypeFoldable};
use rustc::traits;
use rustc::middle::expr_use_visitor as euv;
use rustc::middle::mem_categorization as mc;
@@ -73,18 +73,25 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
_ => return,
}
// Allows these to be passed by value.
let fn_trait = need!(cx.tcx.lang_items().fn_trait());
let asref_trait = need!(get_trait_def_id(cx, &paths::ASREF_TRAIT));
let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
let fn_trait = need!(cx.tcx.lang_items().fn_trait());
let sized_trait = need!(cx.tcx.lang_items().sized_trait());
let fn_def_id = cx.tcx.hir.local_def_id(node_id);
let preds: Vec<ty::Predicate> = {
traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
.filter(|p| !p.is_global())
.collect()
};
let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
.filter(|p| !p.is_global())
.collect::<Vec<_>>();
let preds = preds
.iter()
.filter_map(|pred| if let ty::Predicate::Trait(ref poly_trait_ref) = *pred {
Some(poly_trait_ref.skip_binder())
} else {
None
})
.filter(|t| t.def_id() != sized_trait && !t.has_escaping_regions())
.collect::<Vec<_>>();
// Collect moved variables and spans which will need dereferencings from the
// function body.
@@ -103,40 +110,44 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);
for ((input, &ty), arg) in decl.inputs.iter().zip(fn_sig.inputs()).zip(&body.arguments) {
// Determines whether `ty` implements `Borrow<U>` (U != ty) specifically.
// This is needed due to the `Borrow<T> for T` blanket impl.
let implements_borrow_trait = preds
.iter()
.filter_map(|pred| if let ty::Predicate::Trait(ref poly_trait_ref) = *pred {
Some(poly_trait_ref.skip_binder())
} else {
None
})
.filter(|tpred| tpred.def_id() == borrow_trait && tpred.self_ty() == ty)
.any(|tpred| {
tpred
.input_types()
.nth(1)
.expect("Borrow trait must have an parameter") != ty
});
// * Exclude a type that is specifically bounded by `Borrow`.
// * Exclude a type whose reference also fulfills its bound.
// (e.g. `std::borrow::Borrow`, `serde::Serialize`)
let (implements_borrow_trait, all_borrowable_trait) = {
let preds = preds
.iter()
.filter(|t| t.self_ty() == ty)
.collect::<Vec<_>>();
(
preds.iter().any(|t| t.def_id() == borrow_trait),
!preds.is_empty() && preds.iter().all(|t| {
implements_trait(
cx,
cx.tcx.mk_imm_ref(&RegionKind::ReErased, ty),
t.def_id(),
&t.input_types().skip(1).collect::<Vec<_>>(),
)
}),
)
};
if_let_chain! {[
!is_self(arg),
!ty.is_mutable_pointer(),
!is_copy(cx, ty),
!implements_trait(cx, ty, fn_trait, &[]),
!implements_trait(cx, ty, asref_trait, &[]),
!implements_borrow_trait,
!all_borrowable_trait,
let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node,
!moved_vars.contains(&canonical_id),
], {
// Note: `toplevel_ref_arg` warns if `BindByRef`
if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut {
continue;
}
// Suggestion logic
// Dereference suggestion
let sugg = |db: &mut DiagnosticBuilder| {
let deref_span = spans_need_deref.get(&canonical_id);
if_let_chain! {[
@@ -152,33 +163,37 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
"consider changing the type to",
slice_ty);
assert!(deref_span.is_none());
return; // `Vec` and `String` cannot be destructured - no need for `*` suggestion
return; // `Vec` cannot be destructured - no need for `*` suggestion
}}
if match_type(cx, ty, &paths::STRING) {
db.span_suggestion(input.span,
"consider changing the type to",
"&str".to_string());
db.span_suggestion(input.span, "consider changing the type to", "&str".to_string());
assert!(deref_span.is_none());
return;
return; // ditto
}
let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
// Suggests adding `*` to dereference the added reference.
if let Some(deref_span) = deref_span {
spans.extend(deref_span.iter().cloned()
.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))));
spans.extend(
deref_span
.iter()
.cloned()
.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))),
);
spans.sort_by_key(|&(span, _)| span);
}
multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
};
span_lint_and_then(cx,
NEEDLESS_PASS_BY_VALUE,
input.span,
"this argument is passed by value, but not consumed in the function body",
sugg);
span_lint_and_then(
cx,
NEEDLESS_PASS_BY_VALUE,
input.span,
"this argument is passed by value, but not consumed in the function body",
sugg,
);
}}
}
}
@@ -188,8 +203,7 @@ struct MovedVariablesCtxt<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
moved_vars: HashSet<NodeId>,
/// Spans which need to be prefixed with `*` for dereferencing the
/// suggested additional
/// reference.
/// suggested additional reference.
spans_need_deref: HashMap<NodeId, HashSet<Span>>,
}
@@ -213,9 +227,7 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: mc::cmt<'tcx>) {
let cmt = unwrap_downcast_or_interior(cmt);
if_let_chain! {[
let mc::Categorization::Local(vid) = cmt.cat,
], {
if let mc::Categorization::Local(vid) = cmt.cat {
let mut id = matched_pat.id;
loop {
let parent = self.cx.tcx.hir.get_parent_node(id);
@@ -235,7 +247,7 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
.or_insert_with(HashSet::new)
.insert(c.span);
}
}
},
map::Node::NodeStmt(s) => {
// `let <pat> = x;`
@@ -251,13 +263,13 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
.map(|e| e.span)
.expect("`let` stmt without init aren't caught by match_pat"));
}}
}
},
_ => {}
_ => {},
}
}
}
}}
}
}
}