Enum rustc_mir::borrow_check::nll::type_check::Locations[][src]

pub enum Locations {
    All,
    Boring(Location),
    Interesting(Location),
}
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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

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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.

🔬 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?

A "boring" constraint (caused by the given location) is one that the user probably doesn't want to see described in diagnostics, because it is kind of an artifact of the type system setup.

Example: x = Foo { field: y } technically creates intermediate regions representing the "type of Foo { field: y }", and data flows from y into those variables, but they are not very interesting. The assignment into x on the other hand might be.

🔬 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?

An important outlives constraint (caused by the given location) is one that would be useful to highlight in diagnostics, because it represents a point where references flow from one spot to another (e.g., x = y)

Methods

impl Locations
[src]

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

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🔬 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?

Gets a span representing the location.

Trait Implementations

impl Copy for Locations
[src]

impl Clone for Locations
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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl PartialEq for Locations
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This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

impl Eq for Locations
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impl PartialOrd for Locations
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This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

impl Ord for Locations
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This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

impl Hash for Locations
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Feeds this value into the given [Hasher]. Read more

Feeds a slice of this type into the given [Hasher]. Read more

impl Debug for Locations
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Formats the value using the given formatter. Read more

impl NormalizeLocation for Locations
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🔬 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?

Auto Trait Implementations

impl Send for Locations

impl Sync for Locations