2 use crate::rustc::hir::*;
3 use crate::rustc::hir::intravisit::FnKind;
4 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
5 use crate::rustc::{declare_tool_lint, lint_array};
6 use if_chain::if_chain;
7 use crate::rustc::ty::{self, RegionKind, TypeFoldable};
8 use crate::rustc::traits;
9 use crate::rustc::middle::expr_use_visitor as euv;
10 use crate::rustc::middle::mem_categorization as mc;
11 use crate::rustc_target::spec::abi::Abi;
12 use crate::rustc_data_structures::fx::{FxHashMap, FxHashSet};
13 use crate::syntax::ast::NodeId;
14 use crate::syntax_pos::Span;
15 use crate::syntax::errors::DiagnosticBuilder;
16 use crate::utils::{get_trait_def_id, implements_trait, in_macro, is_copy, is_self, match_type, multispan_sugg, paths,
17 snippet, snippet_opt, span_lint_and_then};
18 use crate::utils::ptr::get_spans;
20 use crate::rustc_errors::Applicability;
22 /// **What it does:** Checks for functions taking arguments by value, but not
23 /// consuming them in its
26 /// **Why is this bad?** Taking arguments by reference is more flexible and can
28 /// unnecessary allocations.
30 /// **Known problems:**
31 /// * This lint suggests taking an argument by reference,
32 /// however sometimes it is better to let users decide the argument type
33 /// (by using `Borrow` trait, for example), depending on how the function is used.
37 /// fn foo(v: Vec<i32>) {
38 /// assert_eq!(v.len(), 42);
41 /// fn foo(v: &[i32]) {
42 /// assert_eq!(v.len(), 42);
45 declare_clippy_lint! {
46 pub NEEDLESS_PASS_BY_VALUE,
48 "functions taking arguments by value, but not consuming them in its body"
51 pub struct NeedlessPassByValue;
53 impl LintPass for NeedlessPassByValue {
54 fn get_lints(&self) -> LintArray {
55 lint_array![NEEDLESS_PASS_BY_VALUE]
60 ($e: expr) => { if let Some(x) = $e { x } else { return; } };
63 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
66 cx: &LateContext<'a, 'tcx>,
78 FnKind::ItemFn(.., header, _, attrs) => {
79 if header.abi != Abi::Rust {
83 if a.meta_item_list().is_some() && a.name() == "proc_macro_derive" {
88 FnKind::Method(..) => (),
92 // Exclude non-inherent impls
93 if let Some(Node::Item(item)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(node_id)) {
94 if matches!(item.node, ItemKind::Impl(_, _, _, _, Some(_), _, _) |
101 // Allow `Borrow` or functions to be taken by value
102 let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
103 let whitelisted_traits = [
104 need!(cx.tcx.lang_items().fn_trait()),
105 need!(cx.tcx.lang_items().fn_once_trait()),
106 need!(cx.tcx.lang_items().fn_mut_trait()),
107 need!(get_trait_def_id(cx, &paths::RANGE_ARGUMENT_TRAIT))
110 let sized_trait = need!(cx.tcx.lang_items().sized_trait());
112 let fn_def_id = cx.tcx.hir.local_def_id(node_id);
114 let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
115 .filter(|p| !p.is_global())
117 if let ty::Predicate::Trait(poly_trait_ref) = pred {
118 if poly_trait_ref.def_id() == sized_trait || poly_trait_ref.skip_binder().has_escaping_regions() {
126 .collect::<Vec<_>>();
128 // Collect moved variables and spans which will need dereferencings from the
130 let MovedVariablesCtxt {
135 let mut ctx = MovedVariablesCtxt::new(cx);
136 let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id);
137 euv::ExprUseVisitor::new(&mut ctx, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None)
142 let fn_sig = cx.tcx.fn_sig(fn_def_id);
143 let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);
145 for (idx, ((input, &ty), arg)) in decl.inputs
147 .zip(fn_sig.inputs())
148 .zip(&body.arguments)
151 // All spans generated from a proc-macro invocation are the same...
152 if span == input.span {
158 if let PatKind::Binding(_, _, ident, ..) = arg.pat.node {
159 if ident.as_str() == "self" {
165 // * Exclude a type that is specifically bounded by `Borrow`.
166 // * Exclude a type whose reference also fulfills its bound.
167 // (e.g. `std::convert::AsRef`, `serde::Serialize`)
168 let (implements_borrow_trait, all_borrowable_trait) = {
171 .filter(|t| t.skip_binder().self_ty() == ty)
172 .collect::<Vec<_>>();
175 preds.iter().any(|t| t.def_id() == borrow_trait),
176 !preds.is_empty() && preds.iter().all(|t| {
179 cx.tcx.mk_imm_ref(&RegionKind::ReErased, ty),
185 .collect::<Vec<_>>(),
193 if !ty.is_mutable_pointer();
195 if !whitelisted_traits.iter().any(|&t| implements_trait(cx, ty, t, &[]));
196 if !implements_borrow_trait;
197 if !all_borrowable_trait;
199 if let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node;
200 if !moved_vars.contains(&canonical_id);
202 if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut {
206 // Dereference suggestion
207 let sugg = |db: &mut DiagnosticBuilder<'_>| {
208 if let ty::TyKind::Adt(def, ..) = ty.sty {
209 if let Some(span) = cx.tcx.hir.span_if_local(def.did) {
210 if cx.param_env.can_type_implement_copy(cx.tcx, ty).is_ok() {
211 db.span_help(span, "consider marking this type as Copy");
216 let deref_span = spans_need_deref.get(&canonical_id);
218 if match_type(cx, ty, &paths::VEC);
219 if let Some(clone_spans) =
220 get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]);
221 if let TyKind::Path(QPath::Resolved(_, ref path)) = input.node;
222 if let Some(elem_ty) = path.segments.iter()
223 .find(|seg| seg.ident.name == "Vec")
224 .and_then(|ps| ps.args.as_ref())
225 .map(|params| params.args.iter().find_map(|arg| match arg {
226 GenericArg::Type(ty) => Some(ty),
227 GenericArg::Lifetime(_) => None,
230 let slice_ty = format!("&[{}]", snippet(cx, elem_ty.span, "_"));
231 db.span_suggestion_with_applicability(
233 "consider changing the type to",
235 Applicability::Unspecified,
238 for (span, suggestion) in clone_spans {
239 db.span_suggestion_with_applicability(
241 &snippet_opt(cx, span)
243 "change the call to".into(),
244 |x| Cow::from(format!("change `{}` to", x)),
247 Applicability::Unspecified,
251 // cannot be destructured, no need for `*` suggestion
252 assert!(deref_span.is_none());
257 if match_type(cx, ty, &paths::STRING) {
258 if let Some(clone_spans) =
259 get_spans(cx, Some(body.id()), idx, &[("clone", ".to_string()"), ("as_str", "")]) {
260 db.span_suggestion_with_applicability(
262 "consider changing the type to",
264 Applicability::Unspecified,
267 for (span, suggestion) in clone_spans {
268 db.span_suggestion_with_applicability(
270 &snippet_opt(cx, span)
272 "change the call to".into(),
273 |x| Cow::from(format!("change `{}` to", x))
276 Applicability::Unspecified,
280 assert!(deref_span.is_none());
285 let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
287 // Suggests adding `*` to dereference the added reference.
288 if let Some(deref_span) = deref_span {
293 .map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))),
295 spans.sort_by_key(|&(span, _)| span);
297 multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
302 NEEDLESS_PASS_BY_VALUE,
304 "this argument is passed by value, but not consumed in the function body",
313 struct MovedVariablesCtxt<'a, 'tcx: 'a> {
314 cx: &'a LateContext<'a, 'tcx>,
315 moved_vars: FxHashSet<NodeId>,
316 /// Spans which need to be prefixed with `*` for dereferencing the
317 /// suggested additional reference.
318 spans_need_deref: FxHashMap<NodeId, FxHashSet<Span>>,
321 impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
322 fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
325 moved_vars: FxHashSet::default(),
326 spans_need_deref: FxHashMap::default(),
330 fn move_common(&mut self, _consume_id: NodeId, _span: Span, cmt: &mc::cmt_<'tcx>) {
331 let cmt = unwrap_downcast_or_interior(cmt);
333 if let mc::Categorization::Local(vid) = cmt.cat {
334 self.moved_vars.insert(vid);
338 fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: &mc::cmt_<'tcx>) {
339 let cmt = unwrap_downcast_or_interior(cmt);
341 if let mc::Categorization::Local(vid) = cmt.cat {
342 let mut id = matched_pat.id;
344 let parent = self.cx.tcx.hir.get_parent_node(id);
351 if let Some(node) = self.cx.tcx.hir.find(id) {
354 // `match` and `if let`
355 if let ExprKind::Match(ref c, ..) = e.node {
356 self.spans_need_deref
358 .or_insert_with(FxHashSet::default)
366 if let StmtKind::Decl(ref decl, _) = s.node;
367 if let DeclKind::Local(ref local) = decl.node;
369 self.spans_need_deref
371 .or_insert_with(FxHashSet::default)
375 .expect("`let` stmt without init aren't caught by match_pat"));
388 impl<'a, 'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> {
389 fn consume(&mut self, consume_id: NodeId, consume_span: Span, cmt: &mc::cmt_<'tcx>, mode: euv::ConsumeMode) {
390 if let euv::ConsumeMode::Move(_) = mode {
391 self.move_common(consume_id, consume_span, cmt);
395 fn matched_pat(&mut self, matched_pat: &Pat, cmt: &mc::cmt_<'tcx>, mode: euv::MatchMode) {
396 if let euv::MatchMode::MovingMatch = mode {
397 self.move_common(matched_pat.id, matched_pat.span, cmt);
399 self.non_moving_pat(matched_pat, cmt);
403 fn consume_pat(&mut self, consume_pat: &Pat, cmt: &mc::cmt_<'tcx>, mode: euv::ConsumeMode) {
404 if let euv::ConsumeMode::Move(_) = mode {
405 self.move_common(consume_pat.id, consume_pat.span, cmt);
409 fn borrow(&mut self, _: NodeId, _: Span, _: &mc::cmt_<'tcx>, _: ty::Region<'_>, _: ty::BorrowKind, _: euv::LoanCause) {}
411 fn mutate(&mut self, _: NodeId, _: Span, _: &mc::cmt_<'tcx>, _: euv::MutateMode) {}
413 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
417 fn unwrap_downcast_or_interior<'a, 'tcx>(mut cmt: &'a mc::cmt_<'tcx>) -> mc::cmt_<'tcx> {
420 mc::Categorization::Downcast(ref c, _) | mc::Categorization::Interior(ref c, _) => {
423 _ => return (*cmt).clone(),