| use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then}; |
| use clippy_utils::ptr::get_spans; |
| use clippy_utils::source::{snippet, snippet_opt}; |
| use clippy_utils::ty::{ |
| implements_trait, implements_trait_with_env_from_iter, is_copy, is_type_diagnostic_item, is_type_lang_item, |
| }; |
| use clippy_utils::{get_trait_def_id, is_self, paths}; |
| use if_chain::if_chain; |
| use rustc_ast::ast::Attribute; |
| use rustc_errors::{Applicability, Diagnostic}; |
| use rustc_hir::intravisit::FnKind; |
| use rustc_hir::{ |
| BindingAnnotation, Body, FnDecl, GenericArg, HirId, HirIdSet, Impl, ItemKind, LangItem, Mutability, Node, PatKind, |
| QPath, TyKind, |
| }; |
| use rustc_hir_typeck::expr_use_visitor as euv; |
| use rustc_infer::infer::TyCtxtInferExt; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::mir::FakeReadCause; |
| use rustc_middle::ty::{self, Ty, TypeVisitableExt}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::def_id::LocalDefId; |
| use rustc_span::symbol::kw; |
| use rustc_span::{sym, Span}; |
| use rustc_target::spec::abi::Abi; |
| use rustc_trait_selection::traits; |
| use rustc_trait_selection::traits::misc::type_allowed_to_implement_copy; |
| |
| 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); |
| /// } |
| /// ``` |
| /// should be |
| /// ```rust |
| /// fn foo(v: &[i32]) { |
| /// assert_eq!(v.len(), 42); |
| /// } |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| 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 { |
| #[expect(clippy::too_many_lines)] |
| fn check_fn( |
| &mut self, |
| cx: &LateContext<'tcx>, |
| kind: FnKind<'tcx>, |
| decl: &'tcx FnDecl<'_>, |
| body: &'tcx Body<'_>, |
| span: Span, |
| fn_def_id: LocalDefId, |
| ) { |
| if span.from_expansion() { |
| return; |
| } |
| |
| let hir_id = cx.tcx.hir().local_def_id_to_hir_id(fn_def_id); |
| |
| match kind { |
| FnKind::ItemFn(.., header) => { |
| let attrs = cx.tcx.hir().attrs(hir_id); |
| 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_parent(hir_id) { |
| if matches!( |
| item.kind, |
| ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..) |
| ) { |
| return; |
| } |
| } |
| |
| // Allow `Borrow` or functions to be taken by value |
| 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 preds = traits::elaborate(cx.tcx, cx.param_env.caller_bounds().iter()) |
| .filter(|p| !p.is_global()) |
| .filter_map(|pred| { |
| // Note that we do not want to deal with qualified predicates here. |
| match pred.kind().no_bound_vars() { |
| Some(ty::ClauseKind::Trait(pred)) if pred.def_id() != sized_trait => Some(pred), |
| _ => None, |
| } |
| }) |
| .collect::<Vec<_>>(); |
| |
| // Collect moved variables and spans which will need dereferencings from the |
| // function body. |
| let MovedVariablesCtxt { moved_vars } = { |
| let mut ctx = MovedVariablesCtxt::default(); |
| let infcx = cx.tcx.infer_ctxt().build(); |
| euv::ExprUseVisitor::new(&mut ctx, &infcx, fn_def_id, cx.param_env, cx.typeck_results()).consume_body(body); |
| ctx |
| }; |
| |
| let fn_sig = cx.tcx.fn_sig(fn_def_id).instantiate_identity(); |
| let fn_sig = cx.tcx.liberate_late_bound_regions(fn_def_id.to_def_id(), 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.name == kw::SelfLower { |
| 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.self_ty() == ty).collect::<Vec<_>>(); |
| |
| ( |
| preds.iter().any(|t| cx.tcx.is_diagnostic_item(sym::Borrow, t.def_id())), |
| !preds.is_empty() && { |
| let ty_empty_region = Ty::new_imm_ref(cx.tcx, cx.tcx.lifetimes.re_erased, ty); |
| preds.iter().all(|t| { |
| let ty_params = t.trait_ref.args.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 ty.is_sized(cx.tcx, cx.param_env); |
| if !allowed_traits.iter().any(|&t| implements_trait_with_env_from_iter( |
| cx.tcx, |
| cx.param_env, |
| ty, |
| t, |
| [Option::<ty::GenericArg<'tcx>>::None], |
| )); |
| if !implements_borrow_trait; |
| if !all_borrowable_trait; |
| |
| if let PatKind::Binding(BindingAnnotation(_, Mutability::Not), canonical_id, ..) = arg.pat.kind; |
| if !moved_vars.contains(&canonical_id); |
| then { |
| // Dereference suggestion |
| let sugg = |diag: &mut Diagnostic| { |
| if let ty::Adt(def, ..) = ty.kind() { |
| if let Some(span) = cx.tcx.hir().span_if_local(def.did()) { |
| if type_allowed_to_implement_copy( |
| cx.tcx, |
| cx.param_env, |
| ty, |
| traits::ObligationCause::dummy_with_span(span), |
| ).is_ok() { |
| diag.span_help(span, "consider marking this type as `Copy`"); |
| } |
| } |
| } |
| |
| if_chain! { |
| if is_type_diagnostic_item(cx, ty, sym::Vec); |
| if let Some(clone_spans) = |
| get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]); |
| if let TyKind::Path(QPath::Resolved(_, 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| format!("change `{x}` to"), |
| ), |
| suggestion, |
| Applicability::Unspecified, |
| ); |
| } |
| |
| // cannot be destructured, no need for `*` suggestion |
| return; |
| } |
| } |
| |
| if is_type_lang_item(cx, ty, LangItem::String) { |
| 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", |
| Applicability::Unspecified, |
| ); |
| |
| for (span, suggestion) in clone_spans { |
| diag.span_suggestion( |
| span, |
| snippet_opt(cx, span) |
| .map_or( |
| "change the call to".into(), |
| |x| format!("change `{x}` to") |
| ), |
| suggestion, |
| Applicability::Unspecified, |
| ); |
| } |
| |
| return; |
| } |
| } |
| |
| let spans = vec![(input.span, format!("&{}", snippet(cx, input.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. |
| pub(crate) 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.has_name(allow)) |
| }) |
| } |
| |
| #[derive(Default)] |
| struct MovedVariablesCtxt { |
| moved_vars: HirIdSet, |
| } |
| |
| 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>, _: HirId) { |
| self.move_common(cmt); |
| } |
| |
| fn borrow(&mut self, _: &euv::PlaceWithHirId<'tcx>, _: HirId, _: ty::BorrowKind) {} |
| |
| fn mutate(&mut self, _: &euv::PlaceWithHirId<'tcx>, _: HirId) {} |
| |
| fn fake_read(&mut self, _: &rustc_hir_typeck::expr_use_visitor::PlaceWithHirId<'tcx>, _: FakeReadCause, _: HirId) {} |
| } |