use crate::utils::ptr::get_spans; use crate::utils::{ get_trait_def_id, implements_trait, in_macro_or_desugar, is_copy, is_self, match_type, multispan_sugg, paths, snippet, snippet_opt, span_lint_and_then, }; use if_chain::if_chain; use matches::matches; use rustc::hir::intravisit::FnKind; use rustc::hir::*; use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; use rustc::middle::expr_use_visitor as euv; use rustc::middle::mem_categorization as mc; use rustc::traits; use rustc::ty::{self, RegionKind, TypeFoldable}; use rustc::{declare_lint_pass, declare_tool_lint}; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_errors::Applicability; use rustc_target::spec::abi::Abi; use std::borrow::Cow; use syntax::ast::Attribute; use syntax::errors::DiagnosticBuilder; use syntax_pos::Span; declare_clippy_lint! { /// **What it does:** Checks for functions taking arguments by value, but not /// consuming them in its /// body. /// /// **Why is this bad?** Taking arguments by reference is more flexible and can /// sometimes avoid /// unnecessary allocations. /// /// **Known problems:** /// * This lint suggests taking an argument by reference, /// however sometimes it is better to let users decide the argument type /// (by using `Borrow` trait, for example), depending on how the function is used. /// /// **Example:** /// ```rust /// fn foo(v: Vec) { /// assert_eq!(v.len(), 42); /// } /// // should be /// fn foo(v: &[i32]) { /// assert_eq!(v.len(), 42); /// } /// ``` pub NEEDLESS_PASS_BY_VALUE, pedantic, "functions taking arguments by value, but not consuming them in its body" } declare_lint_pass!(NeedlessPassByValue => [NEEDLESS_PASS_BY_VALUE]); macro_rules! need { ($e: expr) => { if let Some(x) = $e { x } else { return; } }; } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue { #[allow(clippy::too_many_lines)] fn check_fn( &mut self, cx: &LateContext<'a, 'tcx>, kind: FnKind<'tcx>, decl: &'tcx FnDecl, body: &'tcx Body, span: Span, hir_id: HirId, ) { if in_macro_or_desugar(span) { return; } match kind { FnKind::ItemFn(.., header, _, attrs) => { if header.abi != Abi::Rust || requires_exact_signature(attrs) { return; } }, FnKind::Method(..) => (), _ => return, } // Exclude non-inherent impls if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) { if matches!(item.node, ItemKind::Impl(_, _, _, _, Some(_), _, _) | ItemKind::Trait(..)) { return; } } // Allow `Borrow` or functions to be taken by value let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT)); let whitelisted_traits = [ need!(cx.tcx.lang_items().fn_trait()), need!(cx.tcx.lang_items().fn_once_trait()), need!(cx.tcx.lang_items().fn_mut_trait()), need!(get_trait_def_id(cx, &paths::RANGE_ARGUMENT_TRAIT)), ]; let sized_trait = need!(cx.tcx.lang_items().sized_trait()); let fn_def_id = cx.tcx.hir().local_def_id(hir_id); 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_bound_vars() { return None; } Some(poly_trait_ref) } else { None } }) .collect::>(); // Collect moved variables and spans which will need dereferencings from the // function body. let MovedVariablesCtxt { moved_vars, spans_need_deref, .. } = { let mut ctx = MovedVariablesCtxt::new(cx); let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id); euv::ExprUseVisitor::new( &mut ctx, cx.tcx, fn_def_id, cx.param_env, region_scope_tree, cx.tables, None, ) .consume_body(body); ctx }; let fn_sig = cx.tcx.fn_sig(fn_def_id); let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig); for (idx, ((input, &ty), arg)) in decl.inputs.iter().zip(fn_sig.inputs()).zip(&body.arguments).enumerate() { // All spans generated from a proc-macro invocation are the same... if span == input.span { return; } // Ignore `self`s. if idx == 0 { if let PatKind::Binding(.., ident, _) = arg.pat.node { if ident.as_str() == "self" { continue; } } } // // * 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::>(); ( preds.iter().any(|t| t.def_id() == borrow_trait), !preds.is_empty() && preds.iter().all(|t| { let ty_params = &t .skip_binder() .trait_ref .substs .iter() .skip(1) .cloned() .collect::>(); implements_trait(cx, cx.tcx.mk_imm_ref(&RegionKind::ReEmpty, ty), t.def_id(), ty_params) }), ) }; if_chain! { if !is_self(arg); if !ty.is_mutable_ptr(); if !is_copy(cx, ty); if !whitelisted_traits.iter().any(|&t| implements_trait(cx, ty, t, &[])); if !implements_borrow_trait; if !all_borrowable_trait; if let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node; if !moved_vars.contains(&canonical_id); then { if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut { continue; } // Dereference suggestion let sugg = |db: &mut DiagnosticBuilder<'_>| { if let ty::Adt(def, ..) = ty.sty { if let Some(span) = cx.tcx.hir().span_if_local(def.did) { if cx.param_env.can_type_implement_copy(cx.tcx, ty).is_ok() { db.span_help(span, "consider marking this type as Copy"); } } } let deref_span = spans_need_deref.get(&canonical_id); if_chain! { if match_type(cx, ty, &paths::VEC); if let Some(clone_spans) = get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]); if let TyKind::Path(QPath::Resolved(_, ref path)) = input.node; if let Some(elem_ty) = path.segments.iter() .find(|seg| seg.ident.name == sym!(Vec)) .and_then(|ps| ps.args.as_ref()) .map(|params| params.args.iter().find_map(|arg| match arg { GenericArg::Type(ty) => Some(ty), _ => None, }).unwrap()); then { let slice_ty = format!("&[{}]", snippet(cx, elem_ty.span, "_")); db.span_suggestion( input.span, "consider changing the type to", slice_ty, Applicability::Unspecified, ); 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(), Applicability::Unspecified, ); } // cannot be destructured, no need for `*` suggestion assert!(deref_span.is_none()); return; } } if match_type(cx, ty, &paths::STRING) { 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(), Applicability::Unspecified, ); 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(), Applicability::Unspecified, ); } 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, "")))), ); 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, ); } } } } } /// Functions marked with these attributes must have the exact signature. fn requires_exact_signature(attrs: &[Attribute]) -> bool { attrs.iter().any(|attr| { [sym!(proc_macro), sym!(proc_macro_attribute), sym!(proc_macro_derive)] .iter() .any(|&allow| attr.check_name(allow)) }) } struct MovedVariablesCtxt<'a, 'tcx> { cx: &'a LateContext<'a, 'tcx>, moved_vars: FxHashSet, /// Spans which need to be prefixed with `*` for dereferencing the /// suggested additional reference. spans_need_deref: FxHashMap>, } impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> { fn new(cx: &'a LateContext<'a, 'tcx>) -> Self { Self { cx, moved_vars: FxHashSet::default(), spans_need_deref: FxHashMap::default(), } } fn move_common(&mut self, _consume_id: HirId, _span: Span, cmt: &mc::cmt_<'tcx>) { let cmt = unwrap_downcast_or_interior(cmt); if let mc::Categorization::Local(vid) = cmt.cat { self.moved_vars.insert(vid); } } fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: &mc::cmt_<'tcx>) { let cmt = unwrap_downcast_or_interior(cmt); if let mc::Categorization::Local(vid) = cmt.cat { let mut id = matched_pat.hir_id; loop { let parent = self.cx.tcx.hir().get_parent_node(id); if id == parent { // no parent return; } id = parent; if let Some(node) = self.cx.tcx.hir().find(id) { match node { Node::Expr(e) => { // `match` and `if let` if let ExprKind::Match(ref c, ..) = e.node { self.spans_need_deref .entry(vid) .or_insert_with(FxHashSet::default) .insert(c.span); } }, Node::Stmt(s) => { // `let = x;` if_chain! { if let StmtKind::Local(ref local) = s.node; then { self.spans_need_deref .entry(vid) .or_insert_with(FxHashSet::default) .insert(local.init .as_ref() .map(|e| e.span) .expect("`let` stmt without init aren't caught by match_pat")); } } }, _ => {}, } } } } } } impl<'a, 'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> { fn consume(&mut self, consume_id: HirId, consume_span: Span, cmt: &mc::cmt_<'tcx>, mode: euv::ConsumeMode) { if let euv::ConsumeMode::Move(_) = mode { self.move_common(consume_id, consume_span, cmt); } } fn matched_pat(&mut self, matched_pat: &Pat, cmt: &mc::cmt_<'tcx>, mode: euv::MatchMode) { if let euv::MatchMode::MovingMatch = mode { self.move_common(matched_pat.hir_id, matched_pat.span, cmt); } else { self.non_moving_pat(matched_pat, cmt); } } fn consume_pat(&mut self, consume_pat: &Pat, cmt: &mc::cmt_<'tcx>, mode: euv::ConsumeMode) { if let euv::ConsumeMode::Move(_) = mode { self.move_common(consume_pat.hir_id, consume_pat.span, cmt); } } fn borrow( &mut self, _: HirId, _: Span, _: &mc::cmt_<'tcx>, _: ty::Region<'_>, _: ty::BorrowKind, _: euv::LoanCause, ) { } fn mutate(&mut self, _: HirId, _: Span, _: &mc::cmt_<'tcx>, _: euv::MutateMode) {} fn decl_without_init(&mut self, _: HirId, _: Span) {} } fn unwrap_downcast_or_interior<'a, 'tcx>(mut cmt: &'a mc::cmt_<'tcx>) -> mc::cmt_<'tcx> { loop { match cmt.cat { mc::Categorization::Downcast(ref c, _) | mc::Categorization::Interior(ref c, _) => { cmt = c; }, _ => return (*cmt).clone(), } } }