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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::*;
use rustc::hir::intravisit::FnKind; use rustc::hir::intravisit::FnKind;
use rustc::lint::*; use rustc::lint::*;
use rustc::ty::{self, TypeFoldable}; use rustc::ty::{self, RegionKind, TypeFoldable};
use rustc::traits; use rustc::traits;
use rustc::middle::expr_use_visitor as euv; use rustc::middle::expr_use_visitor as euv;
use rustc::middle::mem_categorization as mc; use rustc::middle::mem_categorization as mc;
@@ -73,18 +73,25 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
_ => return, _ => 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 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 fn_def_id = cx.tcx.hir.local_def_id(node_id);
let preds: Vec<ty::Predicate> = { let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec()) .filter(|p| !p.is_global())
.filter(|p| !p.is_global()) .collect::<Vec<_>>();
.collect() 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 // Collect moved variables and spans which will need dereferencings from the
// function body. // 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); 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) { for ((input, &ty), arg) in decl.inputs.iter().zip(fn_sig.inputs()).zip(&body.arguments) {
// Determines whether `ty` implements `Borrow<U>` (U != ty) specifically. // * Exclude a type that is specifically bounded by `Borrow`.
// This is needed due to the `Borrow<T> for T` blanket impl. // * Exclude a type whose reference also fulfills its bound.
let implements_borrow_trait = preds // (e.g. `std::borrow::Borrow`, `serde::Serialize`)
.iter() let (implements_borrow_trait, all_borrowable_trait) = {
.filter_map(|pred| if let ty::Predicate::Trait(ref poly_trait_ref) = *pred { let preds = preds
Some(poly_trait_ref.skip_binder()) .iter()
} else { .filter(|t| t.self_ty() == ty)
None .collect::<Vec<_>>();
})
.filter(|tpred| tpred.def_id() == borrow_trait && tpred.self_ty() == ty) (
.any(|tpred| { preds.iter().any(|t| t.def_id() == borrow_trait),
tpred !preds.is_empty() && preds.iter().all(|t| {
.input_types() implements_trait(
.nth(1) cx,
.expect("Borrow trait must have an parameter") != ty cx.tcx.mk_imm_ref(&RegionKind::ReErased, ty),
}); t.def_id(),
&t.input_types().skip(1).collect::<Vec<_>>(),
)
}),
)
};
if_let_chain! {[ if_let_chain! {[
!is_self(arg), !is_self(arg),
!ty.is_mutable_pointer(), !ty.is_mutable_pointer(),
!is_copy(cx, ty), !is_copy(cx, ty),
!implements_trait(cx, ty, fn_trait, &[]), !implements_trait(cx, ty, fn_trait, &[]),
!implements_trait(cx, ty, asref_trait, &[]),
!implements_borrow_trait, !implements_borrow_trait,
!all_borrowable_trait,
let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node, let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node,
!moved_vars.contains(&canonical_id), !moved_vars.contains(&canonical_id),
], { ], {
// Note: `toplevel_ref_arg` warns if `BindByRef`
if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut { if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut {
continue; continue;
} }
// Suggestion logic // Dereference suggestion
let sugg = |db: &mut DiagnosticBuilder| { let sugg = |db: &mut DiagnosticBuilder| {
let deref_span = spans_need_deref.get(&canonical_id); let deref_span = spans_need_deref.get(&canonical_id);
if_let_chain! {[ if_let_chain! {[
@@ -152,33 +163,37 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
"consider changing the type to", "consider changing the type to",
slice_ty); slice_ty);
assert!(deref_span.is_none()); 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) { if match_type(cx, ty, &paths::STRING) {
db.span_suggestion(input.span, db.span_suggestion(input.span, "consider changing the type to", "&str".to_string());
"consider changing the type to",
"&str".to_string());
assert!(deref_span.is_none()); assert!(deref_span.is_none());
return; return; // ditto
} }
let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))]; let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
// Suggests adding `*` to dereference the added reference. // Suggests adding `*` to dereference the added reference.
if let Some(deref_span) = deref_span { if let Some(deref_span) = deref_span {
spans.extend(deref_span.iter().cloned() spans.extend(
.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>"))))); deref_span
.iter()
.cloned()
.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))),
);
spans.sort_by_key(|&(span, _)| span); spans.sort_by_key(|&(span, _)| span);
} }
multispan_sugg(db, "consider taking a reference instead".to_string(), spans); multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
}; };
span_lint_and_then(cx, span_lint_and_then(
NEEDLESS_PASS_BY_VALUE, cx,
input.span, NEEDLESS_PASS_BY_VALUE,
"this argument is passed by value, but not consumed in the function body", input.span,
sugg); "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>, cx: &'a LateContext<'a, 'tcx>,
moved_vars: HashSet<NodeId>, moved_vars: HashSet<NodeId>,
/// Spans which need to be prefixed with `*` for dereferencing the /// Spans which need to be prefixed with `*` for dereferencing the
/// suggested additional /// suggested additional reference.
/// reference.
spans_need_deref: HashMap<NodeId, HashSet<Span>>, 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>) { fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: mc::cmt<'tcx>) {
let cmt = unwrap_downcast_or_interior(cmt); let cmt = unwrap_downcast_or_interior(cmt);
if_let_chain! {[ if let mc::Categorization::Local(vid) = cmt.cat {
let mc::Categorization::Local(vid) = cmt.cat,
], {
let mut id = matched_pat.id; let mut id = matched_pat.id;
loop { loop {
let parent = self.cx.tcx.hir.get_parent_node(id); 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) .or_insert_with(HashSet::new)
.insert(c.span); .insert(c.span);
} }
} },
map::Node::NodeStmt(s) => { map::Node::NodeStmt(s) => {
// `let <pat> = x;` // `let <pat> = x;`
@@ -251,13 +263,13 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
.map(|e| e.span) .map(|e| e.span)
.expect("`let` stmt without init aren't caught by match_pat")); .expect("`let` stmt without init aren't caught by match_pat"));
}} }}
} },
_ => {} _ => {},
} }
} }
} }
}} }
} }
} }

19
tests/ui/needless_pass_by_value.rs
View File

@@ -4,6 +4,9 @@
#![warn(needless_pass_by_value)] #![warn(needless_pass_by_value)]
#![allow(dead_code, single_match, if_let_redundant_pattern_matching, many_single_char_names)] #![allow(dead_code, single_match, if_let_redundant_pattern_matching, many_single_char_names)]
use std::borrow::Borrow;
use std::convert::AsRef;
// `v` should be warned // `v` should be warned
// `w`, `x` and `y` are allowed (moved or mutated) // `w`, `x` and `y` are allowed (moved or mutated)
fn foo<T: Default>(v: Vec<T>, w: Vec<T>, mut x: Vec<T>, y: Vec<T>) -> Vec<T> { fn foo<T: Default>(v: Vec<T>, w: Vec<T>, mut x: Vec<T>, y: Vec<T>) -> Vec<T> {
@@ -25,10 +28,11 @@ fn bar(x: String, y: Wrapper) {
assert_eq!(y.0.len(), 42); assert_eq!(y.0.len(), 42);
} }
// U implements `Borrow<U>`, but should be warned correctly // V implements `Borrow<V>`, but should be warned correctly
fn test_borrow_trait<T: std::borrow::Borrow<str>, U>(t: T, u: U) { fn test_borrow_trait<T: Borrow<str>, U: AsRef<str>, V>(t: T, u: U, v: V) {
println!("{}", t.borrow()); println!("{}", t.borrow());
consume(&u); println!("{}", u.as_ref());
consume(&v);
} }
// ok // ok
@@ -59,4 +63,13 @@ fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
println!("{}", t); println!("{}", t);
} }
trait Foo {}
// `S: Serialize` can be passed by value
trait Serialize {}
impl<'a, T> Serialize for &'a T where T: Serialize {}
impl Serialize for i32 {}
fn test_blanket_ref<T: Foo, S: Serialize>(_foo: T, _serializable: S) {}
fn main() {} fn main() {}

56
tests/ui/needless_pass_by_value.stderr
View File

@@ -1,58 +1,64 @@
error: this argument is passed by value, but not consumed in the function body error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:9:23 --> $DIR/needless_pass_by_value.rs:12:23
| |
9 | fn foo<T: Default>(v: Vec<T>, w: Vec<T>, mut x: Vec<T>, y: Vec<T>) -> Vec<T> { 12 | fn foo<T: Default>(v: Vec<T>, w: Vec<T>, mut x: Vec<T>, y: Vec<T>) -> Vec<T> {
| ^^^^^^ help: consider changing the type to: `&[T]` | ^^^^^^ help: consider changing the type to: `&[T]`
| |
= note: `-D needless-pass-by-value` implied by `-D warnings` = note: `-D needless-pass-by-value` implied by `-D warnings`
error: this argument is passed by value, but not consumed in the function body error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:23:11 --> $DIR/needless_pass_by_value.rs:26:11
| |
23 | fn bar(x: String, y: Wrapper) { 26 | fn bar(x: String, y: Wrapper) {
| ^^^^^^ help: consider changing the type to: `&str` | ^^^^^^ help: consider changing the type to: `&str`
error: this argument is passed by value, but not consumed in the function body error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:23:22 --> $DIR/needless_pass_by_value.rs:26:22
| |
23 | fn bar(x: String, y: Wrapper) { 26 | fn bar(x: String, y: Wrapper) {
| ^^^^^^^ help: consider taking a reference instead: `&Wrapper` | ^^^^^^^ help: consider taking a reference instead: `&Wrapper`
error: this argument is passed by value, but not consumed in the function body error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:29:63 --> $DIR/needless_pass_by_value.rs:32:71
| |
29 | fn test_borrow_trait<T: std::borrow::Borrow<str>, U>(t: T, u: U) { 32 | fn test_borrow_trait<T: Borrow<str>, U: AsRef<str>, V>(t: T, u: U, v: V) {
| ^ help: consider taking a reference instead: `&U` | ^ help: consider taking a reference instead: `&V`
error: this argument is passed by value, but not consumed in the function body error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:40:18 --> $DIR/needless_pass_by_value.rs:44:18
| |
40 | fn test_match(x: Option<Option<String>>, y: Option<Option<String>>) { 44 | fn test_match(x: Option<Option<String>>, y: Option<Option<String>>) {
| ^^^^^^^^^^^^^^^^^^^^^^ | ^^^^^^^^^^^^^^^^^^^^^^
| |
help: consider taking a reference instead help: consider taking a reference instead
| |
40 | fn test_match(x: &Option<Option<String>>, y: Option<Option<String>>) { 44 | fn test_match(x: &Option<Option<String>>, y: Option<Option<String>>) {
41 | match *x { 45 | match *x {
| |
error: this argument is passed by value, but not consumed in the function body error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:53:24 --> $DIR/needless_pass_by_value.rs:57:24
| |
53 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) { 57 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
| ^^^^^^^ help: consider taking a reference instead: `&Wrapper` | ^^^^^^^ help: consider taking a reference instead: `&Wrapper`
error: this argument is passed by value, but not consumed in the function body error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:53:36 --> $DIR/needless_pass_by_value.rs:57:36
| |
53 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) { 57 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
| ^^^^^^^ | ^^^^^^^
| |
help: consider taking a reference instead help: consider taking a reference instead
| |
53 | fn test_destructure(x: Wrapper, y: &Wrapper, z: Wrapper) { 57 | fn test_destructure(x: Wrapper, y: &Wrapper, z: Wrapper) {
54 | let Wrapper(s) = z; // moved 58 | let Wrapper(s) = z; // moved
55 | let Wrapper(ref t) = *y; // not moved 59 | let Wrapper(ref t) = *y; // not moved
56 | let Wrapper(_) = *y; // still not moved 60 | let Wrapper(_) = *y; // still not moved
| |
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:73:49
|
73 | fn test_blanket_ref<T: Foo, S: Serialize>(_foo: T, _serializable: S) {}
| ^ help: consider taking a reference instead: `&T`