| //! Checks for uses of const which the type is not `Freeze` (`Cell`-free). |
| //! |
| //! This lint is **warn** by default. |
| |
| use std::ptr; |
| |
| use clippy_utils::diagnostics::span_lint_and_then; |
| use clippy_utils::in_constant; |
| use clippy_utils::macros::macro_backtrace; |
| use if_chain::if_chain; |
| use rustc_hir::def::{DefKind, Res}; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::{ |
| BodyId, Expr, ExprKind, HirId, Impl, ImplItem, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind, UnOp, |
| }; |
| use rustc_hir_analysis::hir_ty_to_ty; |
| use rustc_lint::{LateContext, LateLintPass, Lint}; |
| use rustc_middle::mir; |
| use rustc_middle::mir::interpret::{ConstValue, ErrorHandled}; |
| use rustc_middle::ty::adjustment::Adjust; |
| use rustc_middle::ty::{self, Ty}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::{sym, InnerSpan, Span}; |
| |
| // FIXME: this is a correctness problem but there's no suitable |
| // warn-by-default category. |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks for declaration of `const` items which is interior |
| /// mutable (e.g., contains a `Cell`, `Mutex`, `AtomicXxxx`, etc.). |
| /// |
| /// ### Why is this bad? |
| /// Consts are copied everywhere they are referenced, i.e., |
| /// every time you refer to the const a fresh instance of the `Cell` or `Mutex` |
| /// or `AtomicXxxx` will be created, which defeats the whole purpose of using |
| /// these types in the first place. |
| /// |
| /// The `const` should better be replaced by a `static` item if a global |
| /// variable is wanted, or replaced by a `const fn` if a constructor is wanted. |
| /// |
| /// ### Known problems |
| /// A "non-constant" const item is a legacy way to supply an |
| /// initialized value to downstream `static` items (e.g., the |
| /// `std::sync::ONCE_INIT` constant). In this case the use of `const` is legit, |
| /// and this lint should be suppressed. |
| /// |
| /// Even though the lint avoids triggering on a constant whose type has enums that have variants |
| /// with interior mutability, and its value uses non interior mutable variants (see |
| /// [#3962](https://github.com/rust-lang/rust-clippy/issues/3962) and |
| /// [#3825](https://github.com/rust-lang/rust-clippy/issues/3825) for examples); |
| /// it complains about associated constants without default values only based on its types; |
| /// which might not be preferable. |
| /// There're other enums plus associated constants cases that the lint cannot handle. |
| /// |
| /// Types that have underlying or potential interior mutability trigger the lint whether |
| /// the interior mutable field is used or not. See issues |
| /// [#5812](https://github.com/rust-lang/rust-clippy/issues/5812) and |
| /// |
| /// ### Example |
| /// ```rust |
| /// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; |
| /// |
| /// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12); |
| /// CONST_ATOM.store(6, SeqCst); // the content of the atomic is unchanged |
| /// assert_eq!(CONST_ATOM.load(SeqCst), 12); // because the CONST_ATOM in these lines are distinct |
| /// ``` |
| /// |
| /// Use instead: |
| /// ```rust |
| /// # use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; |
| /// static STATIC_ATOM: AtomicUsize = AtomicUsize::new(15); |
| /// STATIC_ATOM.store(9, SeqCst); |
| /// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| pub DECLARE_INTERIOR_MUTABLE_CONST, |
| style, |
| "declaring `const` with interior mutability" |
| } |
| |
| // FIXME: this is a correctness problem but there's no suitable |
| // warn-by-default category. |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks if `const` items which is interior mutable (e.g., |
| /// contains a `Cell`, `Mutex`, `AtomicXxxx`, etc.) has been borrowed directly. |
| /// |
| /// ### Why is this bad? |
| /// Consts are copied everywhere they are referenced, i.e., |
| /// every time you refer to the const a fresh instance of the `Cell` or `Mutex` |
| /// or `AtomicXxxx` will be created, which defeats the whole purpose of using |
| /// these types in the first place. |
| /// |
| /// The `const` value should be stored inside a `static` item. |
| /// |
| /// ### Known problems |
| /// When an enum has variants with interior mutability, use of its non |
| /// interior mutable variants can generate false positives. See issue |
| /// [#3962](https://github.com/rust-lang/rust-clippy/issues/3962) |
| /// |
| /// Types that have underlying or potential interior mutability trigger the lint whether |
| /// the interior mutable field is used or not. See issues |
| /// [#5812](https://github.com/rust-lang/rust-clippy/issues/5812) and |
| /// [#3825](https://github.com/rust-lang/rust-clippy/issues/3825) |
| /// |
| /// ### Example |
| /// ```rust |
| /// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; |
| /// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12); |
| /// |
| /// CONST_ATOM.store(6, SeqCst); // the content of the atomic is unchanged |
| /// assert_eq!(CONST_ATOM.load(SeqCst), 12); // because the CONST_ATOM in these lines are distinct |
| /// ``` |
| /// |
| /// Use instead: |
| /// ```rust |
| /// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; |
| /// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12); |
| /// |
| /// static STATIC_ATOM: AtomicUsize = CONST_ATOM; |
| /// STATIC_ATOM.store(9, SeqCst); |
| /// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| pub BORROW_INTERIOR_MUTABLE_CONST, |
| style, |
| "referencing `const` with interior mutability" |
| } |
| |
| fn is_unfrozen<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool { |
| // Ignore types whose layout is unknown since `is_freeze` reports every generic types as `!Freeze`, |
| // making it indistinguishable from `UnsafeCell`. i.e. it isn't a tool to prove a type is |
| // 'unfrozen'. However, this code causes a false negative in which |
| // a type contains a layout-unknown type, but also an unsafe cell like `const CELL: Cell<T>`. |
| // Yet, it's better than `ty.has_type_flags(TypeFlags::HAS_TY_PARAM | TypeFlags::HAS_PROJECTION)` |
| // since it works when a pointer indirection involves (`Cell<*const T>`). |
| // Making up a `ParamEnv` where every generic params and assoc types are `Freeze`is another option; |
| // but I'm not sure whether it's a decent way, if possible. |
| cx.tcx.layout_of(cx.param_env.and(ty)).is_ok() && !ty.is_freeze(cx.tcx, cx.param_env) |
| } |
| |
| fn is_value_unfrozen_raw<'tcx>( |
| cx: &LateContext<'tcx>, |
| result: Result<ConstValue<'tcx>, ErrorHandled>, |
| ty: Ty<'tcx>, |
| ) -> bool { |
| fn inner<'tcx>(cx: &LateContext<'tcx>, val: mir::ConstantKind<'tcx>) -> bool { |
| match val.ty().kind() { |
| // the fact that we have to dig into every structs to search enums |
| // leads us to the point checking `UnsafeCell` directly is the only option. |
| ty::Adt(ty_def, ..) if ty_def.is_unsafe_cell() => true, |
| // As of 2022-09-08 miri doesn't track which union field is active so there's no safe way to check the |
| // contained value. |
| ty::Adt(def, ..) if def.is_union() => false, |
| ty::Array(..) | ty::Adt(..) | ty::Tuple(..) => { |
| let val = cx.tcx.destructure_mir_constant(cx.param_env, val); |
| val.fields.iter().any(|field| inner(cx, *field)) |
| }, |
| _ => false, |
| } |
| } |
| result.map_or_else( |
| |err| { |
| // Consider `TooGeneric` cases as being unfrozen. |
| // This causes a false positive where an assoc const whose type is unfrozen |
| // have a value that is a frozen variant with a generic param (an example is |
| // `declare_interior_mutable_const::enums::BothOfCellAndGeneric::GENERIC_VARIANT`). |
| // However, it prevents a number of false negatives that is, I think, important: |
| // 1. assoc consts in trait defs referring to consts of themselves |
| // (an example is `declare_interior_mutable_const::traits::ConcreteTypes::ANOTHER_ATOMIC`). |
| // 2. a path expr referring to assoc consts whose type is doesn't have |
| // any frozen variants in trait defs (i.e. without substitute for `Self`). |
| // (e.g. borrowing `borrow_interior_mutable_const::trait::ConcreteTypes::ATOMIC`) |
| // 3. similar to the false positive above; |
| // but the value is an unfrozen variant, or the type has no enums. (An example is |
| // `declare_interior_mutable_const::enums::BothOfCellAndGeneric::UNFROZEN_VARIANT` |
| // and `declare_interior_mutable_const::enums::BothOfCellAndGeneric::NO_ENUM`). |
| // One might be able to prevent these FNs correctly, and replace this with `false`; |
| // e.g. implementing `has_frozen_variant` described above, and not running this function |
| // when the type doesn't have any frozen variants would be the 'correct' way for the 2nd |
| // case (that actually removes another suboptimal behavior (I won't say 'false positive') where, |
| // similar to 2., but with the a frozen variant) (e.g. borrowing |
| // `borrow_interior_mutable_const::enums::AssocConsts::TO_BE_FROZEN_VARIANT`). |
| // I chose this way because unfrozen enums as assoc consts are rare (or, hopefully, none). |
| err == ErrorHandled::TooGeneric |
| }, |
| |val| inner(cx, mir::ConstantKind::from_value(val, ty)), |
| ) |
| } |
| |
| fn is_value_unfrozen_poly<'tcx>(cx: &LateContext<'tcx>, body_id: BodyId, ty: Ty<'tcx>) -> bool { |
| let result = cx.tcx.const_eval_poly(body_id.hir_id.owner.to_def_id()); |
| is_value_unfrozen_raw(cx, result, ty) |
| } |
| |
| fn is_value_unfrozen_expr<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId, def_id: DefId, ty: Ty<'tcx>) -> bool { |
| let substs = cx.typeck_results().node_substs(hir_id); |
| |
| let result = cx.tcx.const_eval_resolve( |
| cx.param_env, |
| mir::UnevaluatedConst::new(ty::WithOptConstParam::unknown(def_id), substs), |
| None, |
| ); |
| is_value_unfrozen_raw(cx, result, ty) |
| } |
| |
| #[derive(Copy, Clone)] |
| enum Source { |
| Item { item: Span }, |
| Assoc { item: Span }, |
| Expr { expr: Span }, |
| } |
| |
| impl Source { |
| #[must_use] |
| fn lint(&self) -> (&'static Lint, &'static str, Span) { |
| match self { |
| Self::Item { item } | Self::Assoc { item, .. } => ( |
| DECLARE_INTERIOR_MUTABLE_CONST, |
| "a `const` item should never be interior mutable", |
| *item, |
| ), |
| Self::Expr { expr } => ( |
| BORROW_INTERIOR_MUTABLE_CONST, |
| "a `const` item with interior mutability should not be borrowed", |
| *expr, |
| ), |
| } |
| } |
| } |
| |
| fn lint(cx: &LateContext<'_>, source: Source) { |
| let (lint, msg, span) = source.lint(); |
| span_lint_and_then(cx, lint, span, msg, |diag| { |
| if span.from_expansion() { |
| return; // Don't give suggestions into macros. |
| } |
| match source { |
| Source::Item { .. } => { |
| let const_kw_span = span.from_inner(InnerSpan::new(0, 5)); |
| diag.span_label(const_kw_span, "make this a static item (maybe with lazy_static)"); |
| }, |
| Source::Assoc { .. } => (), |
| Source::Expr { .. } => { |
| diag.help("assign this const to a local or static variable, and use the variable here"); |
| }, |
| } |
| }); |
| } |
| |
| declare_lint_pass!(NonCopyConst => [DECLARE_INTERIOR_MUTABLE_CONST, BORROW_INTERIOR_MUTABLE_CONST]); |
| |
| impl<'tcx> LateLintPass<'tcx> for NonCopyConst { |
| fn check_item(&mut self, cx: &LateContext<'tcx>, it: &'tcx Item<'_>) { |
| if let ItemKind::Const(hir_ty, body_id) = it.kind { |
| let ty = hir_ty_to_ty(cx.tcx, hir_ty); |
| if !ignored_macro(cx, it) && is_unfrozen(cx, ty) && is_value_unfrozen_poly(cx, body_id, ty) { |
| lint(cx, Source::Item { item: it.span }); |
| } |
| } |
| } |
| |
| fn check_trait_item(&mut self, cx: &LateContext<'tcx>, trait_item: &'tcx TraitItem<'_>) { |
| if let TraitItemKind::Const(hir_ty, body_id_opt) = &trait_item.kind { |
| let ty = hir_ty_to_ty(cx.tcx, hir_ty); |
| |
| // Normalize assoc types because ones originated from generic params |
| // bounded other traits could have their bound. |
| let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty); |
| if is_unfrozen(cx, normalized) |
| // When there's no default value, lint it only according to its type; |
| // in other words, lint consts whose value *could* be unfrozen, not definitely is. |
| // This feels inconsistent with how the lint treats generic types, |
| // which avoids linting types which potentially become unfrozen. |
| // One could check whether an unfrozen type have a *frozen variant* |
| // (like `body_id_opt.map_or_else(|| !has_frozen_variant(...), ...)`), |
| // and do the same as the case of generic types at impl items. |
| // Note that it isn't sufficient to check if it has an enum |
| // since all of that enum's variants can be unfrozen: |
| // i.e. having an enum doesn't necessary mean a type has a frozen variant. |
| // And, implementing it isn't a trivial task; it'll probably end up |
| // re-implementing the trait predicate evaluation specific to `Freeze`. |
| && body_id_opt.map_or(true, |body_id| is_value_unfrozen_poly(cx, body_id, normalized)) |
| { |
| lint(cx, Source::Assoc { item: trait_item.span }); |
| } |
| } |
| } |
| |
| fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) { |
| if let ImplItemKind::Const(hir_ty, body_id) = &impl_item.kind { |
| let item_def_id = cx.tcx.hir().get_parent_item(impl_item.hir_id()).def_id; |
| let item = cx.tcx.hir().expect_item(item_def_id); |
| |
| match &item.kind { |
| ItemKind::Impl(Impl { |
| of_trait: Some(of_trait_ref), |
| .. |
| }) => { |
| if_chain! { |
| // Lint a trait impl item only when the definition is a generic type, |
| // assuming an assoc const is not meant to be an interior mutable type. |
| if let Some(of_trait_def_id) = of_trait_ref.trait_def_id(); |
| if let Some(of_assoc_item) = cx |
| .tcx |
| .associated_item(impl_item.owner_id) |
| .trait_item_def_id; |
| if cx |
| .tcx |
| .layout_of(cx.tcx.param_env(of_trait_def_id).and( |
| // Normalize assoc types because ones originated from generic params |
| // bounded other traits could have their bound at the trait defs; |
| // and, in that case, the definition is *not* generic. |
| cx.tcx.normalize_erasing_regions( |
| cx.tcx.param_env(of_trait_def_id), |
| cx.tcx.type_of(of_assoc_item).subst_identity(), |
| ), |
| )) |
| .is_err(); |
| // If there were a function like `has_frozen_variant` described above, |
| // we should use here as a frozen variant is a potential to be frozen |
| // similar to unknown layouts. |
| // e.g. `layout_of(...).is_err() || has_frozen_variant(...);` |
| let ty = hir_ty_to_ty(cx.tcx, hir_ty); |
| let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty); |
| if is_unfrozen(cx, normalized); |
| if is_value_unfrozen_poly(cx, *body_id, normalized); |
| then { |
| lint( |
| cx, |
| Source::Assoc { |
| item: impl_item.span, |
| }, |
| ); |
| } |
| } |
| }, |
| ItemKind::Impl(Impl { of_trait: None, .. }) => { |
| let ty = hir_ty_to_ty(cx.tcx, hir_ty); |
| // Normalize assoc types originated from generic params. |
| let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty); |
| |
| if is_unfrozen(cx, ty) && is_value_unfrozen_poly(cx, *body_id, normalized) { |
| lint(cx, Source::Assoc { item: impl_item.span }); |
| } |
| }, |
| _ => (), |
| } |
| } |
| } |
| |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| if let ExprKind::Path(qpath) = &expr.kind { |
| // Only lint if we use the const item inside a function. |
| if in_constant(cx, expr.hir_id) { |
| return; |
| } |
| |
| // Make sure it is a const item. |
| let Res::Def(DefKind::Const | DefKind::AssocConst, item_def_id) = cx.qpath_res(qpath, expr.hir_id) else { |
| return |
| }; |
| |
| // Climb up to resolve any field access and explicit referencing. |
| let mut cur_expr = expr; |
| let mut dereferenced_expr = expr; |
| let mut needs_check_adjustment = true; |
| loop { |
| let parent_id = cx.tcx.hir().parent_id(cur_expr.hir_id); |
| if parent_id == cur_expr.hir_id { |
| break; |
| } |
| if let Some(Node::Expr(parent_expr)) = cx.tcx.hir().find(parent_id) { |
| match &parent_expr.kind { |
| ExprKind::AddrOf(..) => { |
| // `&e` => `e` must be referenced. |
| needs_check_adjustment = false; |
| }, |
| ExprKind::Field(..) => { |
| needs_check_adjustment = true; |
| |
| // Check whether implicit dereferences happened; |
| // if so, no need to go further up |
| // because of the same reason as the `ExprKind::Unary` case. |
| if cx |
| .typeck_results() |
| .expr_adjustments(dereferenced_expr) |
| .iter() |
| .any(|adj| matches!(adj.kind, Adjust::Deref(_))) |
| { |
| break; |
| } |
| |
| dereferenced_expr = parent_expr; |
| }, |
| ExprKind::Index(e, _) if ptr::eq(&**e, cur_expr) => { |
| // `e[i]` => desugared to `*Index::index(&e, i)`, |
| // meaning `e` must be referenced. |
| // no need to go further up since a method call is involved now. |
| needs_check_adjustment = false; |
| break; |
| }, |
| ExprKind::Unary(UnOp::Deref, _) => { |
| // `*e` => desugared to `*Deref::deref(&e)`, |
| // meaning `e` must be referenced. |
| // no need to go further up since a method call is involved now. |
| needs_check_adjustment = false; |
| break; |
| }, |
| _ => break, |
| } |
| cur_expr = parent_expr; |
| } else { |
| break; |
| } |
| } |
| |
| let ty = if needs_check_adjustment { |
| let adjustments = cx.typeck_results().expr_adjustments(dereferenced_expr); |
| if let Some(i) = adjustments |
| .iter() |
| .position(|adj| matches!(adj.kind, Adjust::Borrow(_) | Adjust::Deref(_))) |
| { |
| if i == 0 { |
| cx.typeck_results().expr_ty(dereferenced_expr) |
| } else { |
| adjustments[i - 1].target |
| } |
| } else { |
| // No borrow adjustments means the entire const is moved. |
| return; |
| } |
| } else { |
| cx.typeck_results().expr_ty(dereferenced_expr) |
| }; |
| |
| if is_unfrozen(cx, ty) && is_value_unfrozen_expr(cx, expr.hir_id, item_def_id, ty) { |
| lint(cx, Source::Expr { expr: expr.span }); |
| } |
| } |
| } |
| } |
| |
| fn ignored_macro(cx: &LateContext<'_>, it: &rustc_hir::Item<'_>) -> bool { |
| macro_backtrace(it.span).any(|macro_call| { |
| matches!( |
| cx.tcx.get_diagnostic_name(macro_call.def_id), |
| Some(sym::thread_local_macro) |
| ) |
| }) |
| } |