X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;f=clippy_lints%2Fsrc%2Fnon_copy_const.rs;h=0b2262d849076857ed43d883e3398904e837ff40;hb=feeed17bbaabc9263770eb2740a178c955d173d2;hp=f1df634701dd25d5c7a8e5dfcaa31abaad210426;hpb=b1f0e019fe9609e85f1c356c26d23c0bb423f3e8;p=rust.git diff --git a/clippy_lints/src/non_copy_const.rs b/clippy_lints/src/non_copy_const.rs index f1df634701d..0b2262d8490 100644 --- a/clippy_lints/src/non_copy_const.rs +++ b/clippy_lints/src/non_copy_const.rs @@ -1,20 +1,28 @@ //! Checks for uses of const which the type is not `Freeze` (`Cell`-free). //! -//! This lint is **deny** by default. +//! This lint is **warn** 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_hir::def_id::DefId; +use rustc_hir::{ + BodyId, Expr, ExprKind, HirId, Impl, ImplItem, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind, UnOp, +}; +use rustc_infer::traits::specialization_graph; use rustc_lint::{LateContext, LateLintPass, Lint}; +use rustc_middle::mir::interpret::{ConstValue, ErrorHandled}; use rustc_middle::ty::adjustment::Adjust; -use rustc_middle::ty::{Ty, TypeFlags}; +use rustc_middle::ty::{self, AssocKind, Const, Ty}; 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}; +use crate::utils::{in_constant, span_lint_and_then}; +use if_chain::if_chain; +// 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.). @@ -32,6 +40,18 @@ /// `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}; @@ -47,10 +67,12 @@ /// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance /// ``` pub DECLARE_INTERIOR_MUTABLE_CONST, - correctness, + 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. @@ -62,7 +84,14 @@ /// /// The `const` value should be stored inside a `static` item. /// - /// **Known problems:** None + /// **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 @@ -79,15 +108,87 @@ /// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance /// ``` pub BORROW_INTERIOR_MUTABLE_CONST, - correctness, + style, "referencing `const` with interior mutability" } -#[allow(dead_code)] +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 a unsafe cell like `const CELL: Cell`. + // 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.at(DUMMY_SP), cx.param_env) +} + +fn is_value_unfrozen_raw<'tcx>( + cx: &LateContext<'tcx>, + result: Result, ErrorHandled>, + ty: Ty<'tcx>, +) -> bool { + fn inner<'tcx>(cx: &LateContext<'tcx>, val: &'tcx Const<'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 Some(ty_def.did) == cx.tcx.lang_items().unsafe_cell_type() => true, + ty::Array(..) | ty::Adt(..) | ty::Tuple(..) => { + let val = cx.tcx.destructure_const(cx.param_env.and(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, Const::from_value(cx.tcx, 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, ty::WithOptConstParam::unknown(def_id), substs, None, None); + is_value_unfrozen_raw(cx, result, ty) +} + #[derive(Copy, Clone)] enum Source { Item { item: Span }, - Assoc { item: Span, ty: Span }, + Assoc { item: Span }, Expr { expr: Span }, } @@ -109,14 +210,7 @@ fn lint(&self) -> (&'static Lint, &'static str, Span) { } } -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; - } - +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() { @@ -127,11 +221,7 @@ fn verify_ty_bound<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, source: Source) { 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::Assoc { .. } => (), Source::Expr { .. } => { diag.help("assign this const to a local or static variable, and use the variable here"); }, @@ -143,41 +233,100 @@ fn verify_ty_bound<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, source: Source) { 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 { + if let ItemKind::Const(hir_ty, body_id) = it.kind { let ty = hir_ty_to_ty(cx.tcx, hir_ty); - verify_ty_bound(cx, ty, Source::Item { item: it.span }); + + if 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, ..) = &trait_item.kind { + if let TraitItemKind::Const(hir_ty, body_id_opt) = &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, - }, - ); + + // 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 a 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, ..) = &impl_item.kind { + if let ImplItemKind::Const(hir_ty, body_id) = &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, - }, - ); + + 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 a assoc const is not meant to be a interior mutable type. + if let Some(of_trait_def_id) = of_trait_ref.trait_def_id(); + if let Some(of_assoc_item) = specialization_graph::Node::Trait(of_trait_def_id) + .item(cx.tcx, impl_item.ident, AssocKind::Const, of_trait_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.def_id), + ), + )) + .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(...);` + then { + 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) + && is_value_unfrozen_poly(cx, *body_id, normalized) + { + 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 }); + } + }, + _ => (), } } } @@ -190,8 +339,8 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { } // Make sure it is a const item. - match qpath_res(cx, qpath, expr.hir_id) { - Res::Def(DefKind::Const | DefKind::AssocConst, _) => {}, + let item_def_id = match cx.qpath_res(qpath, expr.hir_id) { + Res::Def(DefKind::Const | DefKind::AssocConst, did) => did, _ => return, }; @@ -234,7 +383,7 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { needs_check_adjustment = false; break; }, - ExprKind::Unary(UnOp::UnDeref, _) => { + 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. @@ -268,7 +417,9 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { cx.typeck_results().expr_ty(dereferenced_expr) }; - verify_ty_bound(cx, ty, Source::Expr { expr: expr.span }); + if is_unfrozen(cx, ty) && is_value_unfrozen_expr(cx, expr.hir_id, item_def_id, ty) { + lint(cx, Source::Expr { expr: expr.span }); + } } } }