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| 1 | +use super::needless_pass_by_value::requires_exact_signature; |
| 2 | +use clippy_utils::diagnostics::span_lint_and_then; |
| 3 | +use clippy_utils::is_self; |
| 4 | +use clippy_utils::source::snippet; |
| 5 | +use if_chain::if_chain; |
| 6 | +use rustc_errors::{Applicability, Diagnostic}; |
| 7 | +use rustc_hir::intravisit::FnKind; |
| 8 | +use rustc_hir::HirIdSet; |
| 9 | +use rustc_hir::{Body, FnDecl, HirId, Impl, ItemKind, Mutability, Node, PatKind}; |
| 10 | +use rustc_hir_typeck::expr_use_visitor as euv; |
| 11 | +use rustc_infer::infer::TyCtxtInferExt; |
| 12 | +use rustc_lint::{LateContext, LateLintPass}; |
| 13 | +use rustc_middle::mir::FakeReadCause; |
| 14 | +use rustc_middle::ty::{self, Ty}; |
| 15 | +use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| 16 | +use rustc_span::def_id::LocalDefId; |
| 17 | +use rustc_span::Span; |
| 18 | +use rustc_target::spec::abi::Abi; |
| 19 | + |
| 20 | +declare_clippy_lint! { |
| 21 | + /// ### What it does |
| 22 | + /// Check if a `&mut` function argument is actually used mutably. |
| 23 | + /// |
| 24 | + /// ### Why is this bad? |
| 25 | + /// Less `mut` means less fights with the borrow checker. It can also lead to more |
| 26 | + /// opportunities for parallelization. |
| 27 | + /// |
| 28 | + /// ### Example |
| 29 | + /// ```rust |
| 30 | + /// fn foo(&mut self, y: &mut i32) -> i32 { |
| 31 | + /// self.x + *y |
| 32 | + /// } |
| 33 | + /// ``` |
| 34 | + /// Use instead: |
| 35 | + /// ```rust |
| 36 | + /// fn foo(&self, y: &i32) -> i32 { |
| 37 | + /// self.x + *y |
| 38 | + /// } |
| 39 | + /// ``` |
| 40 | + #[clippy::version = "1.72.0"] |
| 41 | + pub NEEDLESS_PASS_BY_REF_MUT, |
| 42 | + suspicious, |
| 43 | + "default lint description" |
| 44 | +} |
| 45 | +declare_lint_pass!(NeedlessPassByRefMut => [NEEDLESS_PASS_BY_REF_MUT]); |
| 46 | + |
| 47 | +fn should_skip(span: Span, input: rustc_hir::Ty<'_>, ty: Ty<'_>, arg: &rustc_hir::Param<'_>) -> bool { |
| 48 | + // All spans generated from a proc-macro invocation are the same... |
| 49 | + if span == input.span { |
| 50 | + return true; |
| 51 | + } |
| 52 | + |
| 53 | + if is_self(arg) { |
| 54 | + return true; |
| 55 | + } |
| 56 | + |
| 57 | + !matches!(ty.ref_mutability(), Some(Mutability::Mut)) |
| 58 | +} |
| 59 | + |
| 60 | +impl<'tcx> LateLintPass<'tcx> for NeedlessPassByRefMut { |
| 61 | + fn check_fn( |
| 62 | + &mut self, |
| 63 | + cx: &LateContext<'tcx>, |
| 64 | + kind: FnKind<'tcx>, |
| 65 | + decl: &'tcx FnDecl<'_>, |
| 66 | + body: &'tcx Body<'_>, |
| 67 | + span: Span, |
| 68 | + fn_def_id: LocalDefId, |
| 69 | + ) { |
| 70 | + if span.from_expansion() { |
| 71 | + return; |
| 72 | + } |
| 73 | + |
| 74 | + let hir_id = cx.tcx.hir().local_def_id_to_hir_id(fn_def_id); |
| 75 | + |
| 76 | + match kind { |
| 77 | + FnKind::ItemFn(.., header) => { |
| 78 | + let attrs = cx.tcx.hir().attrs(hir_id); |
| 79 | + if header.abi != Abi::Rust || requires_exact_signature(attrs) { |
| 80 | + return; |
| 81 | + } |
| 82 | + }, |
| 83 | + FnKind::Method(..) => (), |
| 84 | + FnKind::Closure => return, |
| 85 | + } |
| 86 | + |
| 87 | + // Exclude non-inherent impls |
| 88 | + if let Some(Node::Item(item)) = cx.tcx.hir().find_parent(hir_id) { |
| 89 | + if matches!( |
| 90 | + item.kind, |
| 91 | + ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..) |
| 92 | + ) { |
| 93 | + return; |
| 94 | + } |
| 95 | + } |
| 96 | + |
| 97 | + let fn_sig = cx.tcx.fn_sig(fn_def_id).subst_identity(); |
| 98 | + let fn_sig = cx.tcx.liberate_late_bound_regions(fn_def_id.to_def_id(), fn_sig); |
| 99 | + |
| 100 | + // If there are no `&mut` argument, no need to go any further. |
| 101 | + if !decl |
| 102 | + .inputs |
| 103 | + .iter() |
| 104 | + .zip(fn_sig.inputs()) |
| 105 | + .zip(body.params) |
| 106 | + .any(|((&input, &ty), arg)| !should_skip(span, input, ty, arg)) |
| 107 | + { |
| 108 | + return; |
| 109 | + } |
| 110 | + |
| 111 | + // Collect variables mutably used and spans which will need dereferencings from the |
| 112 | + // function body. |
| 113 | + let MutablyUsedVariablesCtxt { mutably_used_vars, .. } = { |
| 114 | + let mut ctx = MutablyUsedVariablesCtxt::default(); |
| 115 | + let infcx = cx.tcx.infer_ctxt().build(); |
| 116 | + euv::ExprUseVisitor::new(&mut ctx, &infcx, fn_def_id, cx.param_env, cx.typeck_results()).consume_body(body); |
| 117 | + ctx |
| 118 | + }; |
| 119 | + |
| 120 | + for ((&input, &ty), arg) in decl.inputs.iter().zip(fn_sig.inputs()).zip(body.params) { |
| 121 | + if should_skip(span, input, ty, arg) { |
| 122 | + continue; |
| 123 | + } |
| 124 | + |
| 125 | + // Only take `&mut` arguments. |
| 126 | + if_chain! { |
| 127 | + if let PatKind::Binding(_, canonical_id, ..) = arg.pat.kind; |
| 128 | + if !mutably_used_vars.contains(&canonical_id); |
| 129 | + if let rustc_hir::TyKind::Ref(_, inner_ty) = input.kind; |
| 130 | + then { |
| 131 | + // If the argument is never used mutably, we emit the error. |
| 132 | + span_lint_and_then( |
| 133 | + cx, |
| 134 | + NEEDLESS_PASS_BY_REF_MUT, |
| 135 | + input.span, |
| 136 | + "this argument is a mutable reference, but not used mutably", |
| 137 | + |diag: &mut Diagnostic| { |
| 138 | + diag.span_suggestion( |
| 139 | + input.span, |
| 140 | + format!( |
| 141 | + "consider changing to &{}", |
| 142 | + snippet(cx, cx.tcx.hir().span(inner_ty.ty.hir_id), "_"), |
| 143 | + ), |
| 144 | + "", |
| 145 | + Applicability::Unspecified, |
| 146 | + ); |
| 147 | + }, |
| 148 | + ); |
| 149 | + } |
| 150 | + } |
| 151 | + } |
| 152 | + } |
| 153 | +} |
| 154 | + |
| 155 | +#[derive(Default)] |
| 156 | +struct MutablyUsedVariablesCtxt { |
| 157 | + mutably_used_vars: HirIdSet, |
| 158 | +} |
| 159 | + |
| 160 | +impl<'tcx> euv::Delegate<'tcx> for MutablyUsedVariablesCtxt { |
| 161 | + fn consume(&mut self, _cmt: &euv::PlaceWithHirId<'tcx>, _id: HirId) {} |
| 162 | + |
| 163 | + fn borrow(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, _id: HirId, borrow: ty::BorrowKind) { |
| 164 | + if borrow == ty::BorrowKind::MutBorrow { |
| 165 | + if let euv::Place { |
| 166 | + base: euv::PlaceBase::Local(vid), |
| 167 | + .. |
| 168 | + } = &cmt.place |
| 169 | + { |
| 170 | + self.mutably_used_vars.insert(*vid); |
| 171 | + } |
| 172 | + } |
| 173 | + } |
| 174 | + |
| 175 | + fn mutate(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, _id: HirId) { |
| 176 | + if let euv::Place { |
| 177 | + projections, |
| 178 | + base: euv::PlaceBase::Local(vid), |
| 179 | + .. |
| 180 | + } = &cmt.place |
| 181 | + { |
| 182 | + if !projections.is_empty() { |
| 183 | + self.mutably_used_vars.insert(*vid); |
| 184 | + } |
| 185 | + } |
| 186 | + } |
| 187 | + |
| 188 | + fn fake_read(&mut self, _: &rustc_hir_typeck::expr_use_visitor::PlaceWithHirId<'tcx>, _: FakeReadCause, _: HirId) {} |
| 189 | +} |
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