Skip to content

Improve needless_pass_by_value #2117

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 4 commits into from
Oct 8, 2017
Merged

Improve needless_pass_by_value #2117

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
bf97cd0
Reduce false-positives for needless_pass_by_value lint
sinkuu Oct 8, 2017
2be6245
Duplicate ptr_arg's suggestion logic
sinkuu Oct 8, 2017
fdc9a64
Exclude Fn traits
sinkuu Oct 8, 2017
8ffec33
Remove intermediate vec
sinkuu Oct 8, 2017
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
161 changes: 108 additions & 53 deletions clippy_lints/src/needless_pass_by_value.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,16 +1,18 @@
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;
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
Expand Down Expand Up @@ -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())
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why is there an intermediate 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.
Expand All @@ -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")
Expand All @@ -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,
);
}}
}
}
Expand All @@ -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>>,
}

Expand All @@ -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);
Expand All @@ -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;`
Expand All @@ -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"));
}}
}
},

_ => {}
_ => {},
}
}
}
}}
}
}
}

Expand Down
71 changes: 5 additions & 66 deletions clippy_lints/src/ptr.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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,
Expand All @@ -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,
Expand Down Expand Up @@ -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))
Expand Down
1 change: 1 addition & 0 deletions clippy_lints/src/utils/mod.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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>>;
Expand Down
Loading