Enum rustc_mir::borrow_check::nll::type_check::Locations

pub enum Locations {
    All,
    Pair {
        from_location: Location,
        at_location: Location,
    },
}

🔬 This is a nightly-only experimental API. (rustc_private)

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The Locations type summarizes where region constraints are required to hold. Normally, this is at a particular point which created the obligation, but for constraints that the user gave, we want the constraint to hold at all points.

Variants

All

🔬 This is a nightly-only experimental API. (rustc_private)

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Indicates that a type constraint should always be true. This is particularly important in the new borrowck analysis for things like the type of the return slot. Consider this example:

fn foo<'a>(x: &'a u32) -> &'a u32 {
    let y = 22;
    return &y; // error
}

Here, we wind up with the signature from the return type being something like &'1 u32 where '1 is a universal region. But the type of the return slot _0 is something like &'2 u32 where '2 is an existential region variable. The type checker requires that &'2 u32 = &'1 u32 -- but at what point? In the older NLL analysis, we required this only at the entry point to the function. By the nature of the constraints, this wound up propagating to all points reachable from start (because '1 -- as a universal region -- is live everywhere). In the newer analysis, though, this doesn't work: _0 is considered dead at the start (it has no usable value) and hence this type equality is basically a no-op. Then, later on, when we do _0 = &'3 y, that region '3 never winds up related to the universal region '1 and hence no error occurs. Therefore, we use Locations::All instead, which ensures that the '1 and '2 are equal everything. We also use this for other user-given type annotations; e.g., if the user wrote let mut x: &'static u32 = ..., we would ensure that all values assigned to x are of 'static lifetime.

Pair

🔬 This is a nightly-only experimental API. (rustc_private)

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Fields of Pair

from_location: Location	🔬 This is a nightly-only experimental API. (rustc_private) this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead? The location in the MIR that generated these constraints. This is intended for error reporting and diagnosis; the constraints may take effect at a distinct spot.
at_location: Location	🔬 This is a nightly-only experimental API. (rustc_private) this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead? The constraints must be met at this location. In terms of the NLL RFC, when you have a constraint R1: R2 @ P, this field is the P value.

Methods

impl Locations

pub fn from_location(&self) -> Option<Location>

🔬 This is a nightly-only experimental API. (rustc_private)

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pub fn at_location(&self) -> Option<Location>

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Trait Implementations

impl Copy for Locations

impl Clone for Locations

fn clone(&self) -> Locations

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Locations

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl ToLocations for Locations

fn to_locations(self) -> Locations

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?