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Merge pull request #2117 from sinkuu/improve_take_by_value 

Improve needless_pass_by_value
This commit is contained in:
Oliver Schneider 2017-10-08 20:14:55 +02:00 committed by GitHub
parent 18483f89aa 8ffec33fd3
commit 73a1dd8e7f
6 changed files with 293 additions and 147 deletions
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161
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;
@ -9,8 +9,10 @@ use syntax::ast::NodeId;
use syntax_pos::Span;
use syntax::errors::DiagnosticBuilder;
use utils::{get_trait_def_id, implements_trait, in_macro, is_copy, is_self, match_type, multispan_sugg, paths,
snippet, span_lint_and_then};
snippet, snippet_opt, span_lint_and_then};
use utils::ptr::get_spans;
use std::collections::{HashMap, HashSet};
use std::borrow::Cow;
/// **What it does:** Checks for functions taking arguments by value, but not
/// consuming them in its
@ -73,18 +75,29 @@ 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));
// Allow `Borrow` or functions to be taken by value
let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
let fn_traits = [
need!(cx.tcx.lang_items().fn_trait()),
need!(cx.tcx.lang_items().fn_once_trait()),
need!(cx.tcx.lang_items().fn_mut_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())
.filter_map(|pred| if let ty::Predicate::Trait(poly_trait_ref) = pred {
if poly_trait_ref.def_id() == sized_trait || poly_trait_ref.skip_binder().has_escaping_regions() {
return None;
}
Some(poly_trait_ref)
} else {
None
})
.collect::<Vec<_>>();
// Collect moved variables and spans which will need dereferencings from the
// function body.
@ -102,45 +115,56 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
let fn_sig = cx.tcx.fn_sig(fn_def_id);
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
});
for (idx, ((input, &ty), arg)) in decl.inputs
.iter()
.zip(fn_sig.inputs())
.zip(&body.arguments)
.enumerate()
{
// * Exclude a type that is specifically bounded by `Borrow`.
// * Exclude a type whose reference also fulfills its bound.
// (e.g. `std::convert::AsRef`, `serde::Serialize`)
let (implements_borrow_trait, all_borrowable_trait) = {
let preds = preds
.iter()
.filter(|t| t.skip_binder().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.skip_binder().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, &[]),
!fn_traits.iter().any(|&t| implements_trait(cx, ty, t, &[])),
!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! {[
match_type(cx, ty, &paths::VEC),
let Some(clone_spans) =
get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]),
let TyPath(QPath::Resolved(_, ref path)) = input.node,
let Some(elem_ty) = path.segments.iter()
.find(|seg| seg.name == "Vec")
@ -151,34 +175,68 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
db.span_suggestion(input.span,
"consider changing the type to",
slice_ty);
for (span, suggestion) in clone_spans {
db.span_suggestion(
span,
&snippet_opt(cx, span)
.map_or(
"change the call to".into(),
|x| Cow::from(format!("change `{}` to", x)),
),
suggestion.into()
);
}
// cannot be destructured, no need for `*` suggestion
assert!(deref_span.is_none());
return; // `Vec` and `String` cannot be destructured - no need for `*` suggestion
return;
}}
if match_type(cx, ty, &paths::STRING) {
db.span_suggestion(input.span,
"consider changing the type to",
"&str".to_string());
assert!(deref_span.is_none());
return;
if let Some(clone_spans) =
get_spans(cx, Some(body.id()), idx, &[("clone", ".to_string()"), ("as_str", "")]) {
db.span_suggestion(input.span, "consider changing the type to", "&str".to_string());
for (span, suggestion) in clone_spans {
db.span_suggestion(
span,
&snippet_opt(cx, span)
.map_or(
"change the call to".into(),
|x| Cow::from(format!("change `{}` to", x))
),
suggestion.into(),
);
}
assert!(deref_span.is_none());
return;
}
}
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 +246,7 @@ 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 +270,7 @@ 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 +290,7 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
.or_insert_with(HashSet::new)
.insert(c.span);
}
}
},
map::Node::NodeStmt(s) => {
// `let <pat> = x;`
@ -251,13 +306,13 @@ impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
.map(|e| e.span)
.expect("`let` stmt without init aren't caught by match_pat"));
}}
}
},
_ => {}
_ => {},
}
}
}
}}
}
}
}

71
clippy_lints/src/ptr.rs
View File

@ -2,16 +2,15 @@
use std::borrow::Cow;
use rustc::hir::*;
use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc::hir::map::NodeItem;
use rustc::lint::*;
use rustc::ty;
use syntax::ast::{Name, NodeId};
use syntax::ast::NodeId;
use syntax::codemap::Span;
use syntax_pos::MultiSpan;
use utils::{get_pat_name, match_qpath, match_type, match_var, paths,
snippet, snippet_opt, span_lint, span_lint_and_then,
use utils::{match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then,
walk_ptrs_hir_ty};
use utils::ptr::get_spans;
/// **What it does:** This lint checks for function arguments of type `&String`
/// or `&Vec` unless the references are mutable. It will also suggest you
@ -164,7 +163,7 @@ fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<
], {
ty_snippet = snippet_opt(cx, parameters.types[0].span);
});
if let Ok(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
span_lint_and_then(
cx,
PTR_ARG,
@ -187,7 +186,7 @@ fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<
);
}
} else if match_type(cx, ty, &paths::STRING) {
if let Ok(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
span_lint_and_then(
cx,
PTR_ARG,
@ -234,66 +233,6 @@ fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<
}
}
fn get_spans(cx: &LateContext, opt_body_id: Option<BodyId>, idx: usize, replacements: &'static [(&'static str, &'static str)]) -> Result<Vec<(Span, Cow<'static, str>)>, ()> {
if let Some(body) = opt_body_id.map(|id| cx.tcx.hir.body(id)) {
get_binding_name(&body.arguments[idx]).map_or_else(|| Ok(vec![]),
|name| extract_clone_suggestions(cx, name, replacements, body))
} else {
Ok(vec![])
}
}
fn extract_clone_suggestions<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, name: Name, replace: &'static [(&'static str, &'static str)], body: &'tcx Body) -> Result<Vec<(Span, Cow<'static, str>)>, ()> {
let mut visitor = PtrCloneVisitor {
cx,
name,
replace,
spans: vec![],
abort: false,
};
visitor.visit_body(body);
if visitor.abort { Err(()) } else { Ok(visitor.spans) }
}
struct PtrCloneVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
name: Name,
replace: &'static [(&'static str, &'static str)],
spans: Vec<(Span, Cow<'static, str>)>,
abort: bool,
}
impl<'a, 'tcx: 'a> Visitor<'tcx> for PtrCloneVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if self.abort { return; }
if let ExprMethodCall(ref seg, _, ref args) = expr.node {
if args.len() == 1 && match_var(&args[0], self.name) {
if seg.name == "capacity" {
self.abort = true;
return;
}
for &(fn_name, suffix) in self.replace {
if seg.name == fn_name {
self.spans.push((expr.span, snippet(self.cx, args[0].span, "_") + suffix));
return;
}
}
}
return;
}
walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn get_binding_name(arg: &Arg) -> Option<Name> {
get_pat_name(&arg.pat)
}
fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
if let Ty_::TyRptr(ref lt, ref m) = ty.node {
Some((lt, m.mutbl, ty.span))

1
clippy_lints/src/utils/mod.rs
View File

@ -32,6 +32,7 @@ pub mod sugg;
pub mod inspector;
pub mod internal_lints;
pub mod author;
pub mod ptr;
pub use self::hir_utils::{SpanlessEq, SpanlessHash};
pub type MethodArgs = HirVec<P<Expr>>;

83
clippy_lints/src/utils/ptr.rs Normal file
View File

@ -0,0 +1,83 @@
use std::borrow::Cow;
use rustc::hir::*;
use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc::lint::LateContext;
use syntax::ast::Name;
use syntax::codemap::Span;
use utils::{get_pat_name, match_var, snippet};
pub fn get_spans(
cx: &LateContext,
opt_body_id: Option<BodyId>,
idx: usize,
replacements: &'static [(&'static str, &'static str)],
) -> Option<Vec<(Span, Cow<'static, str>)>> {
if let Some(body) = opt_body_id.map(|id| cx.tcx.hir.body(id)) {
get_binding_name(&body.arguments[idx])
.map_or_else(|| Some(vec![]), |name| extract_clone_suggestions(cx, name, replacements, body))
} else {
Some(vec![])
}
}
fn extract_clone_suggestions<'a, 'tcx: 'a>(
cx: &LateContext<'a, 'tcx>,
name: Name,
replace: &'static [(&'static str, &'static str)],
body: &'tcx Body,
) -> Option<Vec<(Span, Cow<'static, str>)>> {
let mut visitor = PtrCloneVisitor {
cx,
name,
replace,
spans: vec![],
abort: false,
};
visitor.visit_body(body);
if visitor.abort {
None
} else {
Some(visitor.spans)
}
}
struct PtrCloneVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
name: Name,
replace: &'static [(&'static str, &'static str)],
spans: Vec<(Span, Cow<'static, str>)>,
abort: bool,
}
impl<'a, 'tcx: 'a> Visitor<'tcx> for PtrCloneVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if self.abort {
return;
}
if let ExprMethodCall(ref seg, _, ref args) = expr.node {
if args.len() == 1 && match_var(&args[0], self.name) {
if seg.name == "capacity" {
self.abort = true;
return;
}
for &(fn_name, suffix) in self.replace {
if seg.name == fn_name {
self.spans
.push((expr.span, snippet(self.cx, args[0].span, "_") + suffix));
return;
}
}
}
return;
}
walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn get_binding_name(arg: &Arg) -> Option<Name> {
get_pat_name(&arg.pat)
}

26
tests/ui/needless_pass_by_value.rs
View File

@ -4,6 +4,9 @@
#![warn(needless_pass_by_value)]
#![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
// `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> {
@ -25,10 +28,11 @@ fn bar(x: String, y: Wrapper) {
assert_eq!(y.0.len(), 42);
}
// U implements `Borrow<U>`, but should be warned correctly
fn test_borrow_trait<T: std::borrow::Borrow<str>, U>(t: T, u: U) {
// V implements `Borrow<V>`, but should be warned correctly
fn test_borrow_trait<T: Borrow<str>, U: AsRef<str>, V>(t: T, u: U, v: V) {
println!("{}", t.borrow());
consume(&u);
println!("{}", u.as_ref());
consume(&v);
}
// ok
@ -59,4 +63,20 @@ fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
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 issue_2114(s: String, t: String, u: Vec<i32>, v: Vec<i32>) {
s.capacity();
let _ = t.clone();
u.capacity();
let _ = v.clone();
}
fn main() {}

98
tests/ui/needless_pass_by_value.stderr
View File

@ -1,58 +1,106 @@
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:9:23
|
9 | 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]`
|
= note: `-D needless-pass-by-value` implied by `-D warnings`
--> $DIR/needless_pass_by_value.rs:12:23
|
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]`
|
= note: `-D needless-pass-by-value` implied by `-D warnings`
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`
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`
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) {
| ^ help: consider taking a reference instead: `&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: `&V`
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
|
40 | fn test_match(x: &Option<Option<String>>, y: Option<Option<String>>) {
41 | match *x {
44 | fn test_match(x: &Option<Option<String>>, y: Option<Option<String>>) {
45 | match *x {
|
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`
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
|
53 | fn test_destructure(x: Wrapper, y: &Wrapper, z: Wrapper) {
54 | let Wrapper(s) = z; // moved
55 | let Wrapper(ref t) = *y; // not moved
56 | let Wrapper(_) = *y; // still not moved
57 | fn test_destructure(x: Wrapper, y: &Wrapper, z: Wrapper) {
58 | let Wrapper(s) = z; // moved
59 | let Wrapper(ref t) = *y; // 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`
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:75:18
|
75 | fn issue_2114(s: String, t: String, u: Vec<i32>, v: Vec<i32>) {
| ^^^^^^ help: consider taking a reference instead: `&String`
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:75:29
|
75 | fn issue_2114(s: String, t: String, u: Vec<i32>, v: Vec<i32>) {
| ^^^^^^
|
help: consider changing the type to
|
75 | fn issue_2114(s: String, t: &str, u: Vec<i32>, v: Vec<i32>) {
| ^^^^
help: change `t.clone()` to
|
77 | let _ = t.to_string();
| ^^^^^^^^^^^^^
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:75:40
|
75 | fn issue_2114(s: String, t: String, u: Vec<i32>, v: Vec<i32>) {
| ^^^^^^^^ help: consider taking a reference instead: `&Vec<i32>`
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:75:53
|
75 | fn issue_2114(s: String, t: String, u: Vec<i32>, v: Vec<i32>) {
| ^^^^^^^^
|
help: consider changing the type to
|
75 | fn issue_2114(s: String, t: String, u: Vec<i32>, v: &[i32]) {
| ^^^^^^
help: change `v.clone()` to
|
79 | let _ = v.to_owned();
| ^^^^^^^^^^^^