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Merge BorrowKind::Unique into BorrowKind::Mut

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Shoyu Vanilla 2024-02-26 01:57:03 +09:00
parent 4a8d0f7f56
commit a336bdc142
7 changed files with 68 additions and 83 deletions
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61
crates/hir-ty/src/mir.rs
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@ -659,66 +659,33 @@ pub enum BorrowKind {
/// We can also report errors with this kind of borrow differently.
Shallow,
/// Data must be immutable but not aliasable. This kind of borrow
/// cannot currently be expressed by the user and is used only in
/// implicit closure bindings. It is needed when the closure is
/// borrowing or mutating a mutable referent, e.g.:
/// ```
/// let mut z = 3;
/// let x: &mut isize = &mut z;
/// let y = || *x += 5;
/// ```
/// If we were to try to translate this closure into a more explicit
/// form, we'd encounter an error with the code as written:
/// ```compile_fail,E0594
/// struct Env<'a> { x: &'a &'a mut isize }
/// let mut z = 3;
/// let x: &mut isize = &mut z;
/// let y = (&mut Env { x: &x }, fn_ptr); // Closure is pair of env and fn
/// fn fn_ptr(env: &mut Env) { **env.x += 5; }
/// ```
/// This is then illegal because you cannot mutate an `&mut` found
/// in an aliasable location. To solve, you'd have to translate with
/// an `&mut` borrow:
/// ```compile_fail,E0596
/// struct Env<'a> { x: &'a mut &'a mut isize }
/// let mut z = 3;
/// let x: &mut isize = &mut z;
/// let y = (&mut Env { x: &mut x }, fn_ptr); // changed from &x to &mut x
/// fn fn_ptr(env: &mut Env) { **env.x += 5; }
/// ```
/// Now the assignment to `**env.x` is legal, but creating a
/// mutable pointer to `x` is not because `x` is not mutable. We
/// could fix this by declaring `x` as `let mut x`. This is ok in
/// user code, if awkward, but extra weird for closures, since the
/// borrow is hidden.
///
/// So we introduce a "unique imm" borrow -- the referent is
/// immutable, but not aliasable. This solves the problem. For
/// simplicity, we don't give users the way to express this
/// borrow, it's just used when translating closures.
Unique,
/// Data is mutable and not aliasable.
Mut {
/// `true` if this borrow arose from method-call auto-ref
/// (i.e., `adjustment::Adjust::Borrow`).
allow_two_phase_borrow: bool,
},
Mut { kind: MutBorrowKind },
}
#[derive(Debug, PartialEq, Eq, Clone, Copy, PartialOrd, Ord)]
pub enum MutBorrowKind {
Default,
/// This borrow arose from method-call auto-ref
/// (i.e., adjustment::Adjust::Borrow).
TwoPhasedBorrow,
/// Data must be immutable but not aliasable. This kind of borrow cannot currently
/// be expressed by the user and is used only in implicit closure bindings.
ClosureCapture,
}
impl BorrowKind {
fn from_hir(m: hir_def::type_ref::Mutability) -> Self {
match m {
hir_def::type_ref::Mutability::Shared => BorrowKind::Shared,
hir_def::type_ref::Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
hir_def::type_ref::Mutability::Mut => BorrowKind::Mut { kind: MutBorrowKind::Default },
}
}
fn from_chalk(m: Mutability) -> Self {
match m {
Mutability::Not => BorrowKind::Shared,
Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
Mutability::Mut => BorrowKind::Mut { kind: MutBorrowKind::Default },
}
}
}