Type Alias TypingMode

pub type TypingMode<'tcx> = TypingMode<TyCtxt<'tcx>>;

Aliased Type

enum TypingMode<'tcx> {
    Coherence,
    Analysis {
        defining_opaque_types: &'tcx RawList<(), LocalDefId>,
    },
    PostBorrowckAnalysis {
        defined_opaque_types: &'tcx RawList<(), LocalDefId>,
    },
    PostAnalysis,
}

Variants

Coherence

When checking whether impls overlap, we check whether any obligations are guaranteed to never hold when unifying the impls. This requires us to be complete: we must never fail to prove something which may actually hold.

In this typing mode we bail with ambiguity in case its not knowable whether a trait goal may hold, e.g. because the trait may get implemented in a downstream or sibling crate.

We also have to be careful when generalizing aliases inside of higher-ranked types to not unnecessarily constrain any inference variables.

Analysis

Analysis includes type inference, checking that items are well-formed, and pretty much everything else which may emit proper type errors to the user.

We only normalize opaque types which may get defined by the current body, which are stored in defining_opaque_types.

We also refuse to project any associated type that is marked default. Non-default (“final”) types are always projected. This is necessary in general for soundness of specialization. However, we could allow projections in fully-monomorphic cases. We choose not to, because we prefer for default type to force the type definition to be treated abstractly by any consumers of the impl. Concretely, that means that the following example will fail to compile:

#![feature(specialization)]
trait Assoc {
    type Output;
}

impl<T> Assoc for T {
    default type Output = bool;
}

fn main() {
    let x: <() as Assoc>::Output = true;
}

Fields

defining_opaque_types: &'tcx RawList<(), LocalDefId>

PostBorrowckAnalysis

Any analysis after borrowck for a given body should be able to use all the hidden types defined by borrowck, without being able to define any new ones.

This is currently only used by the new solver, but should be implemented in the old solver as well.

Fields

defined_opaque_types: &'tcx RawList<(), LocalDefId>

PostAnalysis

After analysis, mostly during codegen and MIR optimizations, we’re able to reveal all opaque types. As the concrete type should never be observable directly by the user, this should not be used by checks which may expose such details to the user.

There are some exceptions to this as for example layout_of and const-evaluation always run in PostAnalysis mode, even when used during analysis. This exposes some information about the underlying type to users, but not the type itself.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes

Size for each variant:

• Coherence: 0 bytes
• Analysis: 8 bytes
• PostBorrowckAnalysis: 8 bytes
• PostAnalysis: 0 bytes