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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::source::snippet; |
| 4 | +use clippy_utils::{is_from_proc_macro, is_self}; |
| 5 | +use if_chain::if_chain; |
| 6 | +use rustc_errors::Applicability; |
| 7 | +use rustc_hir::intravisit::FnKind; |
| 8 | +use rustc_hir::{Body, FnDecl, HirId, Impl, ItemKind, Mutability, Node, PatKind}; |
| 9 | +use rustc_hir::{HirIdMap, HirIdSet}; |
| 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_tool_lint, impl_lint_pass}; |
| 16 | +use rustc_span::def_id::LocalDefId; |
| 17 | +use rustc_span::symbol::kw; |
| 18 | +use rustc_span::Span; |
| 19 | +use rustc_target::spec::abi::Abi; |
| 20 | + |
| 21 | +declare_clippy_lint! { |
| 22 | + /// ### What it does |
| 23 | + /// Check if a `&mut` function argument is actually used mutably. |
| 24 | + /// |
| 25 | + /// Be careful if the function is publically reexported as it would break compatibility with |
| 26 | + /// users of this function. |
| 27 | + /// |
| 28 | + /// ### Why is this bad? |
| 29 | + /// Less `mut` means less fights with the borrow checker. It can also lead to more |
| 30 | + /// opportunities for parallelization. |
| 31 | + /// |
| 32 | + /// ### Example |
| 33 | + /// ```rust |
| 34 | + /// fn foo(y: &mut i32) -> i32 { |
| 35 | + /// 12 + *y |
| 36 | + /// } |
| 37 | + /// ``` |
| 38 | + /// Use instead: |
| 39 | + /// ```rust |
| 40 | + /// fn foo(y: &i32) -> i32 { |
| 41 | + /// 12 + *y |
| 42 | + /// } |
| 43 | + /// ``` |
| 44 | + #[clippy::version = "1.72.0"] |
| 45 | + pub NEEDLESS_PASS_BY_REF_MUT, |
| 46 | + suspicious, |
| 47 | + "using a `&mut` argument when it's not mutated" |
| 48 | +} |
| 49 | + |
| 50 | +#[derive(Copy, Clone)] |
| 51 | +pub struct NeedlessPassByRefMut { |
| 52 | + avoid_breaking_exported_api: bool, |
| 53 | +} |
| 54 | + |
| 55 | +impl NeedlessPassByRefMut { |
| 56 | + pub fn new(avoid_breaking_exported_api: bool) -> Self { |
| 57 | + Self { |
| 58 | + avoid_breaking_exported_api, |
| 59 | + } |
| 60 | + } |
| 61 | +} |
| 62 | + |
| 63 | +impl_lint_pass!(NeedlessPassByRefMut => [NEEDLESS_PASS_BY_REF_MUT]); |
| 64 | + |
| 65 | +fn should_skip<'tcx>( |
| 66 | + cx: &LateContext<'tcx>, |
| 67 | + input: rustc_hir::Ty<'tcx>, |
| 68 | + ty: Ty<'_>, |
| 69 | + arg: &rustc_hir::Param<'_>, |
| 70 | +) -> bool { |
| 71 | + // We check if this a `&mut`. `ref_mutability` returns `None` if it's not a reference. |
| 72 | + if !matches!(ty.ref_mutability(), Some(Mutability::Mut)) { |
| 73 | + return true; |
| 74 | + } |
| 75 | + |
| 76 | + if is_self(arg) { |
| 77 | + return true; |
| 78 | + } |
| 79 | + |
| 80 | + if let PatKind::Binding(.., name, _) = arg.pat.kind { |
| 81 | + // If it's a potentially unused variable, we don't check it. |
| 82 | + if name.name == kw::Underscore || name.as_str().starts_with('_') { |
| 83 | + return true; |
| 84 | + } |
| 85 | + } |
| 86 | + |
| 87 | + // All spans generated from a proc-macro invocation are the same... |
| 88 | + is_from_proc_macro(cx, &input) |
| 89 | +} |
| 90 | + |
| 91 | +impl<'tcx> LateLintPass<'tcx> for NeedlessPassByRefMut { |
| 92 | + fn check_fn( |
| 93 | + &mut self, |
| 94 | + cx: &LateContext<'tcx>, |
| 95 | + kind: FnKind<'tcx>, |
| 96 | + decl: &'tcx FnDecl<'_>, |
| 97 | + body: &'tcx Body<'_>, |
| 98 | + span: Span, |
| 99 | + fn_def_id: LocalDefId, |
| 100 | + ) { |
| 101 | + if span.from_expansion() { |
| 102 | + return; |
| 103 | + } |
| 104 | + |
| 105 | + let hir_id = cx.tcx.hir().local_def_id_to_hir_id(fn_def_id); |
| 106 | + |
| 107 | + match kind { |
| 108 | + FnKind::ItemFn(.., header) => { |
| 109 | + let attrs = cx.tcx.hir().attrs(hir_id); |
| 110 | + if header.abi != Abi::Rust || requires_exact_signature(attrs) { |
| 111 | + return; |
| 112 | + } |
| 113 | + }, |
| 114 | + FnKind::Method(..) => (), |
| 115 | + FnKind::Closure => return, |
| 116 | + } |
| 117 | + |
| 118 | + // Exclude non-inherent impls |
| 119 | + if let Some(Node::Item(item)) = cx.tcx.hir().find_parent(hir_id) { |
| 120 | + if matches!( |
| 121 | + item.kind, |
| 122 | + ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..) |
| 123 | + ) { |
| 124 | + return; |
| 125 | + } |
| 126 | + } |
| 127 | + |
| 128 | + let fn_sig = cx.tcx.fn_sig(fn_def_id).subst_identity(); |
| 129 | + let fn_sig = cx.tcx.liberate_late_bound_regions(fn_def_id.to_def_id(), fn_sig); |
| 130 | + |
| 131 | + // If there are no `&mut` argument, no need to go any further. |
| 132 | + if !decl |
| 133 | + .inputs |
| 134 | + .iter() |
| 135 | + .zip(fn_sig.inputs()) |
| 136 | + .zip(body.params) |
| 137 | + .any(|((&input, &ty), arg)| !should_skip(cx, input, ty, arg)) |
| 138 | + { |
| 139 | + return; |
| 140 | + } |
| 141 | + |
| 142 | + // Collect variables mutably used and spans which will need dereferencings from the |
| 143 | + // function body. |
| 144 | + let MutablyUsedVariablesCtxt { mutably_used_vars, .. } = { |
| 145 | + let mut ctx = MutablyUsedVariablesCtxt::default(); |
| 146 | + let infcx = cx.tcx.infer_ctxt().build(); |
| 147 | + euv::ExprUseVisitor::new(&mut ctx, &infcx, fn_def_id, cx.param_env, cx.typeck_results()).consume_body(body); |
| 148 | + ctx |
| 149 | + }; |
| 150 | + |
| 151 | + let mut it = decl |
| 152 | + .inputs |
| 153 | + .iter() |
| 154 | + .zip(fn_sig.inputs()) |
| 155 | + .zip(body.params) |
| 156 | + .filter(|((&input, &ty), arg)| !should_skip(cx, input, ty, arg)) |
| 157 | + .peekable(); |
| 158 | + if it.peek().is_none() { |
| 159 | + return; |
| 160 | + } |
| 161 | + let show_semver_warning = self.avoid_breaking_exported_api && cx.effective_visibilities.is_exported(fn_def_id); |
| 162 | + for ((&input, &_), arg) in it { |
| 163 | + // Only take `&mut` arguments. |
| 164 | + if_chain! { |
| 165 | + if let PatKind::Binding(_, canonical_id, ..) = arg.pat.kind; |
| 166 | + if !mutably_used_vars.contains(&canonical_id); |
| 167 | + if let rustc_hir::TyKind::Ref(_, inner_ty) = input.kind; |
| 168 | + then { |
| 169 | + // If the argument is never used mutably, we emit the warning. |
| 170 | + let sp = input.span; |
| 171 | + span_lint_and_then( |
| 172 | + cx, |
| 173 | + NEEDLESS_PASS_BY_REF_MUT, |
| 174 | + sp, |
| 175 | + "this argument is a mutable reference, but not used mutably", |
| 176 | + |diag| { |
| 177 | + diag.span_suggestion( |
| 178 | + sp, |
| 179 | + "consider changing to".to_string(), |
| 180 | + format!( |
| 181 | + "&{}", |
| 182 | + snippet(cx, cx.tcx.hir().span(inner_ty.ty.hir_id), "_"), |
| 183 | + ), |
| 184 | + Applicability::Unspecified, |
| 185 | + ); |
| 186 | + if show_semver_warning { |
| 187 | + diag.warn("changing this function will impact semver compatibility"); |
| 188 | + } |
| 189 | + }, |
| 190 | + ); |
| 191 | + } |
| 192 | + } |
| 193 | + } |
| 194 | + } |
| 195 | +} |
| 196 | + |
| 197 | +#[derive(Default)] |
| 198 | +struct MutablyUsedVariablesCtxt { |
| 199 | + mutably_used_vars: HirIdSet, |
| 200 | + prev_bind: Option<HirId>, |
| 201 | + aliases: HirIdMap<HirId>, |
| 202 | +} |
| 203 | + |
| 204 | +impl MutablyUsedVariablesCtxt { |
| 205 | + fn add_mutably_used_var(&mut self, mut used_id: HirId) { |
| 206 | + while let Some(id) = self.aliases.get(&used_id) { |
| 207 | + self.mutably_used_vars.insert(used_id); |
| 208 | + used_id = *id; |
| 209 | + } |
| 210 | + self.mutably_used_vars.insert(used_id); |
| 211 | + } |
| 212 | +} |
| 213 | + |
| 214 | +impl<'tcx> euv::Delegate<'tcx> for MutablyUsedVariablesCtxt { |
| 215 | + fn consume(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, _id: HirId) { |
| 216 | + if let euv::Place { |
| 217 | + base: euv::PlaceBase::Local(vid), |
| 218 | + base_ty, |
| 219 | + .. |
| 220 | + } = &cmt.place |
| 221 | + { |
| 222 | + if let Some(bind_id) = self.prev_bind.take() { |
| 223 | + self.aliases.insert(bind_id, *vid); |
| 224 | + } else if matches!(base_ty.ref_mutability(), Some(Mutability::Mut)) { |
| 225 | + self.add_mutably_used_var(*vid); |
| 226 | + } |
| 227 | + } |
| 228 | + } |
| 229 | + |
| 230 | + fn borrow(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, _id: HirId, borrow: ty::BorrowKind) { |
| 231 | + self.prev_bind = None; |
| 232 | + if let euv::Place { |
| 233 | + base: euv::PlaceBase::Local(vid), |
| 234 | + base_ty, |
| 235 | + .. |
| 236 | + } = &cmt.place |
| 237 | + { |
| 238 | + // If this is a mutable borrow, it was obviously used mutably so we add it. However |
| 239 | + // for `UniqueImmBorrow`, it's interesting because if you do: `array[0] = value` inside |
| 240 | + // a closure, it'll return this variant whereas if you have just an index access, it'll |
| 241 | + // return `ImmBorrow`. So if there is "Unique" and it's a mutable reference, we add it |
| 242 | + // to the mutably used variables set. |
| 243 | + if borrow == ty::BorrowKind::MutBorrow |
| 244 | + || (borrow == ty::BorrowKind::UniqueImmBorrow && base_ty.ref_mutability() == Some(Mutability::Mut)) |
| 245 | + { |
| 246 | + self.add_mutably_used_var(*vid); |
| 247 | + } |
| 248 | + } |
| 249 | + } |
| 250 | + |
| 251 | + fn mutate(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, _id: HirId) { |
| 252 | + self.prev_bind = None; |
| 253 | + if let euv::Place { |
| 254 | + projections, |
| 255 | + base: euv::PlaceBase::Local(vid), |
| 256 | + .. |
| 257 | + } = &cmt.place |
| 258 | + { |
| 259 | + if !projections.is_empty() { |
| 260 | + self.add_mutably_used_var(*vid); |
| 261 | + } |
| 262 | + } |
| 263 | + } |
| 264 | + |
| 265 | + fn copy(&mut self, _cmt: &euv::PlaceWithHirId<'tcx>, _id: HirId) { |
| 266 | + self.prev_bind = None; |
| 267 | + } |
| 268 | + |
| 269 | + fn fake_read(&mut self, _: &rustc_hir_typeck::expr_use_visitor::PlaceWithHirId<'tcx>, _: FakeReadCause, _: HirId) {} |
| 270 | + |
| 271 | + fn bind(&mut self, _cmt: &euv::PlaceWithHirId<'tcx>, id: HirId) { |
| 272 | + self.prev_bind = Some(id); |
| 273 | + } |
| 274 | +} |
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