| use crate::utils::ptr::get_spans; |
| use crate::utils::{ |
| get_trait_def_id, implements_trait, is_copy, is_self, is_type_diagnostic_item, multispan_sugg, paths, snippet, |
| snippet_opt, span_lint_and_then, |
| }; |
| use if_chain::if_chain; |
| use rustc_ast::ast::Attribute; |
| use rustc_data_structures::fx::{FxHashMap, FxHashSet}; |
| use rustc_errors::{Applicability, DiagnosticBuilder}; |
| use rustc_hir::intravisit::FnKind; |
| use rustc_hir::{BindingAnnotation, Body, FnDecl, GenericArg, HirId, ItemKind, Node, PatKind, QPath, TyKind}; |
| use rustc_infer::infer::TyCtxtInferExt; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::ty::{self, TypeFoldable}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::Span; |
| use rustc_target::spec::abi::Abi; |
| use rustc_trait_selection::traits; |
| use rustc_trait_selection::traits::misc::can_type_implement_copy; |
| use rustc_typeck::expr_use_visitor as euv; |
| use std::borrow::Cow; |
| |
| 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<i32>) { |
| /// assert_eq!(v.len(), 42); |
| /// } |
| /// ``` |
| /// |
| /// ```rust |
| /// // 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<'tcx> LateLintPass<'tcx> for NeedlessPassByValue { |
| #[allow(clippy::too_many_lines)] |
| fn check_fn( |
| &mut self, |
| cx: &LateContext<'tcx>, |
| kind: FnKind<'tcx>, |
| decl: &'tcx FnDecl<'_>, |
| body: &'tcx Body<'_>, |
| span: Span, |
| hir_id: HirId, |
| ) { |
| if span.from_expansion() { |
| return; |
| } |
| |
| match kind { |
| FnKind::ItemFn(.., header, _, attrs) => { |
| if header.abi != Abi::Rust || requires_exact_signature(attrs) { |
| return; |
| } |
| }, |
| FnKind::Method(..) => (), |
| FnKind::Closure(..) => 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.kind, ItemKind::Impl{ of_trait: 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 allowed_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().iter()) |
| .filter(|p| !p.is_global()) |
| .filter_map(|obligation| { |
| if let ty::PredicateKind::Trait(poly_trait_ref, _) = obligation.predicate.kind() { |
| 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::<Vec<_>>(); |
| |
| // Collect moved variables and spans which will need dereferencings from the |
| // function body. |
| let MovedVariablesCtxt { |
| moved_vars, |
| spans_need_deref, |
| .. |
| } = { |
| let mut ctx = MovedVariablesCtxt::default(); |
| cx.tcx.infer_ctxt().enter(|infcx| { |
| euv::ExprUseVisitor::new(&mut ctx, &infcx, fn_def_id, cx.param_env, cx.tables()).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.params).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.kind { |
| 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::<Vec<_>>(); |
| |
| ( |
| preds.iter().any(|t| t.def_id() == borrow_trait), |
| !preds.is_empty() && { |
| let ty_empty_region = cx.tcx.mk_imm_ref(cx.tcx.lifetimes.re_root_empty, ty); |
| preds.iter().all(|t| { |
| let ty_params = &t.skip_binder().trait_ref.substs.iter().skip(1).collect::<Vec<_>>(); |
| implements_trait(cx, ty_empty_region, t.def_id(), ty_params) |
| }) |
| }, |
| ) |
| }; |
| |
| if_chain! { |
| if !is_self(arg); |
| if !ty.is_mutable_ptr(); |
| if !is_copy(cx, ty); |
| if !allowed_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.kind; |
| if !moved_vars.contains(&canonical_id); |
| then { |
| if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut { |
| continue; |
| } |
| |
| // Dereference suggestion |
| let sugg = |diag: &mut DiagnosticBuilder<'_>| { |
| if let ty::Adt(def, ..) = ty.kind { |
| if let Some(span) = cx.tcx.hir().span_if_local(def.did) { |
| if can_type_implement_copy(cx.tcx, cx.param_env, ty).is_ok() { |
| diag.span_help(span, "consider marking this type as `Copy`"); |
| } |
| } |
| } |
| |
| let deref_span = spans_need_deref.get(&canonical_id); |
| if_chain! { |
| if is_type_diagnostic_item(cx, ty, sym!(vec_type)); |
| if let Some(clone_spans) = |
| get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]); |
| if let TyKind::Path(QPath::Resolved(_, ref path)) = input.kind; |
| 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, "_")); |
| diag.span_suggestion( |
| input.span, |
| "consider changing the type to", |
| slice_ty, |
| Applicability::Unspecified, |
| ); |
| |
| for (span, suggestion) in clone_spans { |
| diag.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 is_type_diagnostic_item(cx, ty, sym!(string_type)) { |
| if let Some(clone_spans) = |
| get_spans(cx, Some(body.id()), idx, &[("clone", ".to_string()"), ("as_str", "")]) { |
| diag.span_suggestion( |
| input.span, |
| "consider changing the type to", |
| "&str".to_string(), |
| Applicability::Unspecified, |
| ); |
| |
| for (span, suggestion) in clone_spans { |
| diag.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, "<expr>")))), |
| ); |
| spans.sort_by_key(|&(span, _)| span); |
| } |
| multispan_sugg(diag, "consider taking a reference instead", 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)) |
| }) |
| } |
| |
| #[derive(Default)] |
| struct MovedVariablesCtxt { |
| moved_vars: FxHashSet<HirId>, |
| /// Spans which need to be prefixed with `*` for dereferencing the |
| /// suggested additional reference. |
| spans_need_deref: FxHashMap<HirId, FxHashSet<Span>>, |
| } |
| |
| impl MovedVariablesCtxt { |
| fn move_common(&mut self, cmt: &euv::PlaceWithHirId<'_>) { |
| if let euv::PlaceBase::Local(vid) = cmt.place.base { |
| self.moved_vars.insert(vid); |
| } |
| } |
| } |
| |
| impl<'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt { |
| fn consume(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, mode: euv::ConsumeMode) { |
| if let euv::ConsumeMode::Move = mode { |
| self.move_common(cmt); |
| } |
| } |
| |
| fn borrow(&mut self, _: &euv::PlaceWithHirId<'tcx>, _: ty::BorrowKind) {} |
| |
| fn mutate(&mut self, _: &euv::PlaceWithHirId<'tcx>) {} |
| } |