| //! Checks for uses of const which the type is not `Freeze` (`Cell`-free). |
| //! |
| //! This lint is **deny** by default. |
| |
| use std::ptr; |
| |
| use rustc_hir::def::{DefKind, Res}; |
| use rustc_hir::{Expr, ExprKind, ImplItem, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind, UnOp}; |
| use rustc_lint::{LateContext, LateLintPass, Lint}; |
| use rustc_middle::ty::adjustment::Adjust; |
| use rustc_middle::ty::{Ty, TypeFlags}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::{InnerSpan, Span, DUMMY_SP}; |
| use rustc_typeck::hir_ty_to_ty; |
| |
| use crate::utils::{in_constant, is_copy, qpath_res, span_lint_and_then}; |
| |
| 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. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; |
| /// |
| /// // Bad. |
| /// 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 |
| /// |
| /// // Good. |
| /// 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 |
| /// ``` |
| pub DECLARE_INTERIOR_MUTABLE_CONST, |
| correctness, |
| "declaring `const` with interior mutability" |
| } |
| |
| 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:** None |
| /// |
| /// **Example:** |
| /// ```rust |
| /// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; |
| /// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12); |
| /// |
| /// // Bad. |
| /// 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 |
| /// |
| /// // Good. |
| /// 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 |
| /// ``` |
| pub BORROW_INTERIOR_MUTABLE_CONST, |
| correctness, |
| "referencing `const` with interior mutability" |
| } |
| |
| #[allow(dead_code)] |
| #[derive(Copy, Clone)] |
| enum Source { |
| Item { item: Span }, |
| Assoc { item: Span, ty: 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 verify_ty_bound<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, source: Source) { |
| if ty.is_freeze(cx.tcx.at(DUMMY_SP), cx.param_env) || is_copy(cx, ty) { |
| // An `UnsafeCell` is `!Copy`, and an `UnsafeCell` is also the only type which |
| // is `!Freeze`, thus if our type is `Copy` we can be sure it must be `Freeze` |
| // as well. |
| return; |
| } |
| |
| 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 { ty: ty_span, .. } => { |
| if ty.flags.intersects(TypeFlags::HAS_FREE_LOCAL_NAMES) { |
| diag.span_label(ty_span, &format!("consider requiring `{}` to be `Copy`", ty)); |
| } |
| }, |
| 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, ..) = &it.kind { |
| let ty = hir_ty_to_ty(cx.tcx, hir_ty); |
| verify_ty_bound(cx, ty, Source::Item { item: it.span }); |
| } |
| } |
| |
| fn check_trait_item(&mut self, cx: &LateContext<'tcx>, trait_item: &'tcx TraitItem<'_>) { |
| if let TraitItemKind::Const(hir_ty, ..) = &trait_item.kind { |
| let ty = hir_ty_to_ty(cx.tcx, hir_ty); |
| verify_ty_bound( |
| cx, |
| ty, |
| Source::Assoc { |
| ty: hir_ty.span, |
| item: trait_item.span, |
| }, |
| ); |
| } |
| } |
| |
| fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) { |
| if let ImplItemKind::Const(hir_ty, ..) = &impl_item.kind { |
| let item_hir_id = cx.tcx.hir().get_parent_node(impl_item.hir_id); |
| let item = cx.tcx.hir().expect_item(item_hir_id); |
| // Ensure the impl is an inherent impl. |
| if let ItemKind::Impl { of_trait: None, .. } = item.kind { |
| let ty = hir_ty_to_ty(cx.tcx, hir_ty); |
| verify_ty_bound( |
| cx, |
| ty, |
| Source::Assoc { |
| ty: hir_ty.span, |
| 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. |
| match qpath_res(cx, qpath, expr.hir_id) { |
| Res::Def(DefKind::Const | DefKind::AssocConst, _) => {}, |
| _ => 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().get_parent_node(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(..) => { |
| dereferenced_expr = parent_expr; |
| needs_check_adjustment = true; |
| }, |
| 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::UnDeref, _) => { |
| // `*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.tables().expr_adjustments(dereferenced_expr); |
| if let Some(i) = adjustments.iter().position(|adj| match adj.kind { |
| Adjust::Borrow(_) | Adjust::Deref(_) => true, |
| _ => false, |
| }) { |
| if i == 0 { |
| cx.tables().expr_ty(dereferenced_expr) |
| } else { |
| adjustments[i - 1].target |
| } |
| } else { |
| // No borrow adjustments means the entire const is moved. |
| return; |
| } |
| } else { |
| cx.tables().expr_ty(dereferenced_expr) |
| }; |
| |
| verify_ty_bound(cx, ty, Source::Expr { expr: expr.span }); |
| } |
| } |
| } |