34b373d309
This renames the variants in HIR UnOp from
enum UnOp {
UnDeref,
UnNot,
UnNeg,
}
to
enum UnOp {
Deref,
Not,
Neg,
}
Motivations:
- This is more consistent with the rest of the code base where most enum
variants don't have a prefix.
- These variants are never used without the `UnOp` prefix so the extra
`Un` prefix doesn't help with readability. E.g. we don't have any
`UnDeref`s in the code, we only have `UnOp::UnDeref`.
- MIR `UnOp` type variants don't have a prefix so this is more
consistent with MIR types.
- "un" prefix reads like "inverse" or "reverse", so as a beginner in
rustc code base when I see "UnDeref" what comes to my mind is
something like "&*" instead of just "*".
426 lines
20 KiB
Rust
426 lines
20 KiB
Rust
//! Checks for uses of const which the type is not `Freeze` (`Cell`-free).
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//!
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//! This lint is **warn** by default.
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use std::ptr;
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use rustc_hir::def::{DefKind, Res};
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use rustc_hir::def_id::DefId;
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use rustc_hir::{
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BodyId, Expr, ExprKind, HirId, Impl, ImplItem, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind, UnOp,
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};
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use rustc_infer::traits::specialization_graph;
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use rustc_lint::{LateContext, LateLintPass, Lint};
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use rustc_middle::mir::interpret::{ConstValue, ErrorHandled};
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use rustc_middle::ty::adjustment::Adjust;
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use rustc_middle::ty::{self, AssocKind, Const, Ty};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::{InnerSpan, Span, DUMMY_SP};
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use rustc_typeck::hir_ty_to_ty;
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use crate::utils::{in_constant, span_lint_and_then};
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use if_chain::if_chain;
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// FIXME: this is a correctness problem but there's no suitable
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// warn-by-default category.
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declare_clippy_lint! {
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/// **What it does:** Checks for declaration of `const` items which is interior
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/// mutable (e.g., contains a `Cell`, `Mutex`, `AtomicXxxx`, etc.).
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///
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/// **Why is this bad?** Consts are copied everywhere they are referenced, i.e.,
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/// every time you refer to the const a fresh instance of the `Cell` or `Mutex`
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/// or `AtomicXxxx` will be created, which defeats the whole purpose of using
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/// these types in the first place.
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///
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/// The `const` should better be replaced by a `static` item if a global
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/// variable is wanted, or replaced by a `const fn` if a constructor is wanted.
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///
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/// **Known problems:** A "non-constant" const item is a legacy way to supply an
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/// initialized value to downstream `static` items (e.g., the
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/// `std::sync::ONCE_INIT` constant). In this case the use of `const` is legit,
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/// and this lint should be suppressed.
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///
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/// Even though the lint avoids triggering on a constant whose type has enums that have variants
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/// with interior mutability, and its value uses non interior mutable variants (see
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/// [#3962](https://github.com/rust-lang/rust-clippy/issues/3962) and
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/// [#3825](https://github.com/rust-lang/rust-clippy/issues/3825) for examples);
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/// it complains about associated constants without default values only based on its types;
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/// which might not be preferable.
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/// There're other enums plus associated constants cases that the lint cannot handle.
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///
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/// Types that have underlying or potential interior mutability trigger the lint whether
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/// the interior mutable field is used or not. See issues
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/// [#5812](https://github.com/rust-lang/rust-clippy/issues/5812) and
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///
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/// **Example:**
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/// ```rust
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/// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
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///
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/// // Bad.
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/// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12);
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/// CONST_ATOM.store(6, SeqCst); // the content of the atomic is unchanged
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/// assert_eq!(CONST_ATOM.load(SeqCst), 12); // because the CONST_ATOM in these lines are distinct
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///
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/// // Good.
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/// static STATIC_ATOM: AtomicUsize = AtomicUsize::new(15);
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/// STATIC_ATOM.store(9, SeqCst);
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/// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance
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/// ```
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pub DECLARE_INTERIOR_MUTABLE_CONST,
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style,
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"declaring `const` with interior mutability"
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}
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// FIXME: this is a correctness problem but there's no suitable
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// warn-by-default category.
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declare_clippy_lint! {
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/// **What it does:** Checks if `const` items which is interior mutable (e.g.,
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/// contains a `Cell`, `Mutex`, `AtomicXxxx`, etc.) has been borrowed directly.
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///
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/// **Why is this bad?** Consts are copied everywhere they are referenced, i.e.,
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/// every time you refer to the const a fresh instance of the `Cell` or `Mutex`
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/// or `AtomicXxxx` will be created, which defeats the whole purpose of using
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/// these types in the first place.
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///
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/// The `const` value should be stored inside a `static` item.
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///
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/// **Known problems:** When an enum has variants with interior mutability, use of its non
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/// interior mutable variants can generate false positives. See issue
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/// [#3962](https://github.com/rust-lang/rust-clippy/issues/3962)
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///
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/// Types that have underlying or potential interior mutability trigger the lint whether
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/// the interior mutable field is used or not. See issues
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/// [#5812](https://github.com/rust-lang/rust-clippy/issues/5812) and
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/// [#3825](https://github.com/rust-lang/rust-clippy/issues/3825)
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///
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/// **Example:**
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/// ```rust
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/// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
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/// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12);
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///
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/// // Bad.
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/// CONST_ATOM.store(6, SeqCst); // the content of the atomic is unchanged
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/// assert_eq!(CONST_ATOM.load(SeqCst), 12); // because the CONST_ATOM in these lines are distinct
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///
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/// // Good.
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/// static STATIC_ATOM: AtomicUsize = CONST_ATOM;
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/// STATIC_ATOM.store(9, SeqCst);
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/// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance
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/// ```
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pub BORROW_INTERIOR_MUTABLE_CONST,
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style,
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"referencing `const` with interior mutability"
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}
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fn is_unfrozen<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
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// Ignore types whose layout is unknown since `is_freeze` reports every generic types as `!Freeze`,
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// making it indistinguishable from `UnsafeCell`. i.e. it isn't a tool to prove a type is
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// 'unfrozen'. However, this code causes a false negative in which
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// a type contains a layout-unknown type, but also a unsafe cell like `const CELL: Cell<T>`.
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// Yet, it's better than `ty.has_type_flags(TypeFlags::HAS_TY_PARAM | TypeFlags::HAS_PROJECTION)`
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// since it works when a pointer indirection involves (`Cell<*const T>`).
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// Making up a `ParamEnv` where every generic params and assoc types are `Freeze`is another option;
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// but I'm not sure whether it's a decent way, if possible.
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cx.tcx.layout_of(cx.param_env.and(ty)).is_ok() && !ty.is_freeze(cx.tcx.at(DUMMY_SP), cx.param_env)
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}
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fn is_value_unfrozen_raw<'tcx>(
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cx: &LateContext<'tcx>,
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result: Result<ConstValue<'tcx>, ErrorHandled>,
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ty: Ty<'tcx>,
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) -> bool {
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fn inner<'tcx>(cx: &LateContext<'tcx>, val: &'tcx Const<'tcx>) -> bool {
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match val.ty.kind() {
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// the fact that we have to dig into every structs to search enums
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// leads us to the point checking `UnsafeCell` directly is the only option.
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ty::Adt(ty_def, ..) if Some(ty_def.did) == cx.tcx.lang_items().unsafe_cell_type() => true,
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ty::Array(..) | ty::Adt(..) | ty::Tuple(..) => {
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let val = cx.tcx.destructure_const(cx.param_env.and(val));
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val.fields.iter().any(|field| inner(cx, field))
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},
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_ => false,
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}
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}
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result.map_or_else(
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|err| {
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// Consider `TooGeneric` cases as being unfrozen.
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// This causes a false positive where an assoc const whose type is unfrozen
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// have a value that is a frozen variant with a generic param (an example is
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// `declare_interior_mutable_const::enums::BothOfCellAndGeneric::GENERIC_VARIANT`).
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// However, it prevents a number of false negatives that is, I think, important:
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// 1. assoc consts in trait defs referring to consts of themselves
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// (an example is `declare_interior_mutable_const::traits::ConcreteTypes::ANOTHER_ATOMIC`).
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// 2. a path expr referring to assoc consts whose type is doesn't have
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// any frozen variants in trait defs (i.e. without substitute for `Self`).
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// (e.g. borrowing `borrow_interior_mutable_const::trait::ConcreteTypes::ATOMIC`)
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// 3. similar to the false positive above;
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// but the value is an unfrozen variant, or the type has no enums. (An example is
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// `declare_interior_mutable_const::enums::BothOfCellAndGeneric::UNFROZEN_VARIANT`
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// and `declare_interior_mutable_const::enums::BothOfCellAndGeneric::NO_ENUM`).
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// One might be able to prevent these FNs correctly, and replace this with `false`;
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// e.g. implementing `has_frozen_variant` described above, and not running this function
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// when the type doesn't have any frozen variants would be the 'correct' way for the 2nd
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// case (that actually removes another suboptimal behavior (I won't say 'false positive') where,
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// similar to 2., but with the a frozen variant) (e.g. borrowing
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// `borrow_interior_mutable_const::enums::AssocConsts::TO_BE_FROZEN_VARIANT`).
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// I chose this way because unfrozen enums as assoc consts are rare (or, hopefully, none).
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err == ErrorHandled::TooGeneric
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},
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|val| inner(cx, Const::from_value(cx.tcx, val, ty)),
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)
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}
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fn is_value_unfrozen_poly<'tcx>(cx: &LateContext<'tcx>, body_id: BodyId, ty: Ty<'tcx>) -> bool {
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let result = cx.tcx.const_eval_poly(body_id.hir_id.owner.to_def_id());
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is_value_unfrozen_raw(cx, result, ty)
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}
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fn is_value_unfrozen_expr<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId, def_id: DefId, ty: Ty<'tcx>) -> bool {
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let substs = cx.typeck_results().node_substs(hir_id);
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let result = cx
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.tcx
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.const_eval_resolve(cx.param_env, ty::WithOptConstParam::unknown(def_id), substs, None, None);
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is_value_unfrozen_raw(cx, result, ty)
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}
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#[derive(Copy, Clone)]
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enum Source {
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Item { item: Span },
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Assoc { item: Span },
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Expr { expr: Span },
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}
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impl Source {
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#[must_use]
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fn lint(&self) -> (&'static Lint, &'static str, Span) {
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match self {
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Self::Item { item } | Self::Assoc { item, .. } => (
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DECLARE_INTERIOR_MUTABLE_CONST,
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"a `const` item should never be interior mutable",
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*item,
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),
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Self::Expr { expr } => (
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BORROW_INTERIOR_MUTABLE_CONST,
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"a `const` item with interior mutability should not be borrowed",
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*expr,
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),
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}
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}
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}
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fn lint(cx: &LateContext<'_>, source: Source) {
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let (lint, msg, span) = source.lint();
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span_lint_and_then(cx, lint, span, msg, |diag| {
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if span.from_expansion() {
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return; // Don't give suggestions into macros.
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}
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match source {
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Source::Item { .. } => {
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let const_kw_span = span.from_inner(InnerSpan::new(0, 5));
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diag.span_label(const_kw_span, "make this a static item (maybe with lazy_static)");
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},
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Source::Assoc { .. } => (),
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Source::Expr { .. } => {
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diag.help("assign this const to a local or static variable, and use the variable here");
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},
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}
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});
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}
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declare_lint_pass!(NonCopyConst => [DECLARE_INTERIOR_MUTABLE_CONST, BORROW_INTERIOR_MUTABLE_CONST]);
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impl<'tcx> LateLintPass<'tcx> for NonCopyConst {
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fn check_item(&mut self, cx: &LateContext<'tcx>, it: &'tcx Item<'_>) {
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if let ItemKind::Const(hir_ty, body_id) = it.kind {
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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if is_unfrozen(cx, ty) && is_value_unfrozen_poly(cx, body_id, ty) {
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lint(cx, Source::Item { item: it.span });
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}
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}
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}
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fn check_trait_item(&mut self, cx: &LateContext<'tcx>, trait_item: &'tcx TraitItem<'_>) {
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if let TraitItemKind::Const(hir_ty, body_id_opt) = &trait_item.kind {
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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// Normalize assoc types because ones originated from generic params
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// bounded other traits could have their bound.
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let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
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if is_unfrozen(cx, normalized)
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// When there's no default value, lint it only according to its type;
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// in other words, lint consts whose value *could* be unfrozen, not definitely is.
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// This feels inconsistent with how the lint treats generic types,
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// which avoids linting types which potentially become unfrozen.
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// One could check whether a unfrozen type have a *frozen variant*
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// (like `body_id_opt.map_or_else(|| !has_frozen_variant(...), ...)`),
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// and do the same as the case of generic types at impl items.
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// Note that it isn't sufficient to check if it has an enum
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// since all of that enum's variants can be unfrozen:
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// i.e. having an enum doesn't necessary mean a type has a frozen variant.
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// And, implementing it isn't a trivial task; it'll probably end up
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// re-implementing the trait predicate evaluation specific to `Freeze`.
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&& body_id_opt.map_or(true, |body_id| is_value_unfrozen_poly(cx, body_id, normalized))
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{
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lint(cx, Source::Assoc { item: trait_item.span });
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}
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) {
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if let ImplItemKind::Const(hir_ty, body_id) = &impl_item.kind {
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let item_hir_id = cx.tcx.hir().get_parent_node(impl_item.hir_id);
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let item = cx.tcx.hir().expect_item(item_hir_id);
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match &item.kind {
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ItemKind::Impl(Impl {
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of_trait: Some(of_trait_ref),
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..
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}) => {
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if_chain! {
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// Lint a trait impl item only when the definition is a generic type,
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// assuming a assoc const is not meant to be a interior mutable type.
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if let Some(of_trait_def_id) = of_trait_ref.trait_def_id();
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if let Some(of_assoc_item) = specialization_graph::Node::Trait(of_trait_def_id)
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.item(cx.tcx, impl_item.ident, AssocKind::Const, of_trait_def_id);
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if cx
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.tcx
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.layout_of(cx.tcx.param_env(of_trait_def_id).and(
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// Normalize assoc types because ones originated from generic params
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// bounded other traits could have their bound at the trait defs;
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// and, in that case, the definition is *not* generic.
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cx.tcx.normalize_erasing_regions(
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cx.tcx.param_env(of_trait_def_id),
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cx.tcx.type_of(of_assoc_item.def_id),
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),
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))
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.is_err();
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// If there were a function like `has_frozen_variant` described above,
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// we should use here as a frozen variant is a potential to be frozen
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// similar to unknown layouts.
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// e.g. `layout_of(...).is_err() || has_frozen_variant(...);`
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then {
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
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if is_unfrozen(cx, normalized)
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&& is_value_unfrozen_poly(cx, *body_id, normalized)
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{
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lint(
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cx,
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Source::Assoc {
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item: impl_item.span,
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},
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);
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}
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}
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}
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},
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ItemKind::Impl(Impl { of_trait: None, .. }) => {
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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// Normalize assoc types originated from generic params.
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let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
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if is_unfrozen(cx, ty) && is_value_unfrozen_poly(cx, *body_id, normalized) {
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lint(cx, Source::Assoc { item: impl_item.span });
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}
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},
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_ => (),
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}
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}
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}
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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.
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|
if in_constant(cx, expr.hir_id) {
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return;
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}
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// Make sure it is a const item.
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let item_def_id = match cx.qpath_res(qpath, expr.hir_id) {
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Res::Def(DefKind::Const | DefKind::AssocConst, did) => did,
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_ => return,
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};
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// Climb up to resolve any field access and explicit referencing.
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let mut cur_expr = expr;
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let mut dereferenced_expr = expr;
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let mut needs_check_adjustment = true;
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loop {
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let parent_id = cx.tcx.hir().get_parent_node(cur_expr.hir_id);
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|
if parent_id == cur_expr.hir_id {
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break;
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}
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|
if let Some(Node::Expr(parent_expr)) = cx.tcx.hir().find(parent_id) {
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match &parent_expr.kind {
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|
ExprKind::AddrOf(..) => {
|
|
// `&e` => `e` must be referenced.
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needs_check_adjustment = false;
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},
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ExprKind::Field(..) => {
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needs_check_adjustment = true;
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// Check whether implicit dereferences happened;
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|
// if so, no need to go further up
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|
// because of the same reason as the `ExprKind::Unary` case.
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|
if cx
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.typeck_results()
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|
.expr_adjustments(dereferenced_expr)
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|
.iter()
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.any(|adj| matches!(adj.kind, Adjust::Deref(_)))
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{
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break;
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}
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dereferenced_expr = parent_expr;
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},
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ExprKind::Index(e, _) if ptr::eq(&**e, cur_expr) => {
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// `e[i]` => desugared to `*Index::index(&e, i)`,
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|
// meaning `e` must be referenced.
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// no need to go further up since a method call is involved now.
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needs_check_adjustment = false;
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break;
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},
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ExprKind::Unary(UnOp::Deref, _) => {
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// `*e` => desugared to `*Deref::deref(&e)`,
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// meaning `e` must be referenced.
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// no need to go further up since a method call is involved now.
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needs_check_adjustment = false;
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break;
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},
|
|
_ => 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 });
|
|
}
|
|
}
|
|
}
|
|
}
|