TypingMode in rustc_type_ir::infer_ctxt - Rust
Description: The current typing mode of an inference context. We unfortunately have some slightly different typing rules depending on the current context. See the doc comment for each variant for how and why they are used.

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## TypingMode

# Enum TypingMode

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    pub enum TypingMode<I: Interner, S: TypingModeErasedStatus = MayBeErased> {
        Coherence,
        Analysis {
            defining_opaque_types_and_generators: I::LocalDefIds,
        },
        Borrowck {
            defining_opaque_types: I::LocalDefIds,
        },
        PostBorrowckAnalysis {
            defined_opaque_types: I::LocalDefIds,
        },
        PostAnalysis,
        ErasedNotCoherence(S),
    }

Expand description

The current typing mode of an inference context. We unfortunately have some slightly different typing rules depending on the current context. See the doc comment for each variant for how and why they are used.

In most cases you can get the correct typing mode automatically via:

- `mir::Body::typing_mode`
- `rustc_lint::LateContext::typing_mode`

If neither of these functions are available, feel free to reach out to t-types for help.

Because typing rules get subtly different based on what typing mode we’re in, subtle enough that changing the behavior of typing modes can sometimes cause changes that we don’t even have tests for, we’d like to enforce the rule that any place where we specialize behavior based on the typing mode, we match exhaustively on the typing mode. That way, it’s easy to determine all the places that must change when anything about typing modes changes.

Hence, `TypingMode` does not implement `Eq`, though `TypingModeEqWrapper` is available in the rare case that you do need this. Most cases where this currently matters is where we pass typing modes through the query system and want to cache based on it. See also `#[rustc_must_match_exhaustively]`, which tries to detect non-exhaustive matches.

Since matching on typing mode to single out `Coherence` is so common, and `Coherence` is so different from the other modes: see also `is_coherence`

## Variants§

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### 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.

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### 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_and_generators: I::LocalDefIds`
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### Borrowck

The behavior during MIR borrowck is identical to `TypingMode::Analysis` except that the initial value for opaque types is the type computed during HIR typeck with unique unconstrained region inference variables.

This is currently only used with by the new solver as it results in new non-universal defining uses of opaque types, which is a breaking change. See tests/ui/impl-trait/non-defining-use/as-projection-term.rs.

#### Fields

§`defining_opaque_types: I::LocalDefIds`
§

### 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: I::LocalDefIds`
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### PostAnalysis

After analysis, mostly during codegen and MIR optimizations, we’re able to reveal all opaque types. As the hidden 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.

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### ErasedNotCoherence(S)

The typing modes above (except coherence) only differ in how they handle

- Generators
- Opaque types
- Specialization (in `PostAnalysis`)

We replace all of them with this `TypingMode` in the first attempt at canonicalization. If, during that attempt, we try to access information about opaques or generators we bail out, setting a field on `EvalCtxt` that indicates the canonicalization must be rerun in the original typing mode.

`TypingMode::Coherence` is not replaced by this and is always kept as-is.

## Implementations§

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### impl<I: Interner, S: TypingModeErasedStatus> TypingMode<I, S>

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#### pub fn is_coherence(&self) -> bool

There are a bunch of places in the compiler where we single out `Coherence`, and alter behavior. We’d like to always match on `TypingMode` exhaustively, but not having this method leads to a bunch of noisy code.

See also the documentation on `TypingMode` about exhaustive matching.

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#### pub fn is_erased_not_coherence(&self) -> bool

There are a bunch of places in the trait solver where we single out `Coherence`, and alter behavior. We’d like to always match on `TypingMode` exhaustively, but not having this method leads to a bunch of noisy code.

See also the documentation on `TypingMode` about exhaustive matching.

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### impl<I: Interner> TypingMode<I, MayBeErased>

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#### pub fn assert_not_erased(self) -> TypingMode<I, CantBeErased>

Only call this when you’re sure you’re outside the next trait solver! That means either not in the trait solver, or in code that is old-solver only.

See the comment on `InferCtxt::typing_mode_raw`

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### impl<I: Interner> TypingMode<I, CantBeErased>

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#### pub fn non_body_analysis() -> TypingMode<I>

Analysis outside of a body does not define any opaque types.

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#### pub fn typeck_for_body(cx: I, body_def_id: I::LocalDefId) -> TypingMode<I>

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#### pub fn analysis_in_body(cx: I, body_def_id: I::LocalDefId) -> TypingMode<I>

While typechecking a body, we need to be able to define the opaque types defined by that body.

FIXME: This will be removed because it’s generally not correct to define opaques outside of HIR typeck.

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#### pub fn borrowck(cx: I, body_def_id: I::LocalDefId) -> TypingMode<I>

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#### pub fn post_borrowck_analysis( cx: I, body_def_id: I::LocalDefId, ) -> TypingMode<I>

## Trait Implementations§

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### impl<I, S: TypingModeErasedStatus> Clone for TypingMode<I, S>
where I: Interner,

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#### fn clone(&self) -> Self

Returns a duplicate of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl<I, S: TypingModeErasedStatus> Copy for TypingMode<I, S>
where I: Interner,

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### impl<I, S: TypingModeErasedStatus> Debug for TypingMode<I, S>
where I: Interner,

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#### fn fmt(&self, __f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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### impl<I: Interner, S, __D: Decoder> Decodable<__D> for TypingMode<I, S>
where I::LocalDefIds: Decodable<__D>, S: Decodable<__D> + TypingModeErasedStatus,

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#### fn decode(__decoder: &mut __D) -> Self

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### impl<I: Interner, S, __E: Encoder> Encodable<__E> for TypingMode<I, S>
where I::LocalDefIds: Encodable<__E>, S: Encodable<__E> + TypingModeErasedStatus,

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#### fn encode(&self, __encoder: &mut __E)

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### impl<I: Interner> From<TypingMode<I, CantBeErased>> for TypingMode<I, MayBeErased>

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#### fn from(value: TypingMode<I, CantBeErased>) -> Self

Converts to this type from the input type.
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### impl<I, S: TypingModeErasedStatus> Hash for TypingMode<I, S>
where I: Interner,

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#### fn hash<__H: Hasher>(&self, __state: &mut __H)

Feeds this value into the given `Hasher`. Read more
1.3.0 · Source§

#### fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl<I: Interner, S> StableHash for TypingMode<I, S>
where I::LocalDefIds: StableHash, S: StableHash + TypingModeErasedStatus,

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#### fn stable_hash<__Hcx: StableHashCtxt>( &self, __hcx: &mut __Hcx, __hasher: &mut StableHasher, )

## Auto Trait Implementations§

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### impl<I, S> DynSend for TypingMode<I, S>
where <I as Interner>::LocalDefIds: DynSend, S: DynSend,

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### impl<I, S> DynSync for TypingMode<I, S>
where <I as Interner>::LocalDefIds: DynSync, S: DynSync,

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### impl<I, S> Freeze for TypingMode<I, S>
where <I as Interner>::LocalDefIds: Freeze, S: Freeze,

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### impl<I, S> RefUnwindSafe for TypingMode<I, S>
where <I as Interner>::LocalDefIds: RefUnwindSafe, S: RefUnwindSafe,

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### impl<I, S> Send for TypingMode<I, S>
where <I as Interner>::LocalDefIds: Send, S: Send,

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### impl<I, S> Sync for TypingMode<I, S>
where <I as Interner>::LocalDefIds: Sync, S: Sync,

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### impl<I, S> Unpin for TypingMode<I, S>
where <I as Interner>::LocalDefIds: Unpin, S: Unpin,

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### impl<I, S> UnsafeUnpin for TypingMode<I, S>
where <I as Interner>::LocalDefIds: UnsafeUnpin, S: UnsafeUnpin,

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### impl<I, S> UnwindSafe for TypingMode<I, S>
where <I as Interner>::LocalDefIds: UnwindSafe, S: UnwindSafe,

## Blanket Implementations§

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### impl<T> Aligned for T

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#### const ALIGN: Alignment

Alignment of `Self`.
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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T, R> CollectAndApply<T, R> for T

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#### fn collect_and_apply<I, F>(iter: I, f: F) -> R
where I: Iterator<Item = T>, F: FnOnce(&[T]) -> R,

Equivalent to `f(&iter.collect::<Vec<_>>())`.

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#### type Output = R

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### impl<T> ErasedDestructor for T
where T: 'static,

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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T> Instrument for T

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#### fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided `Span`, returning an `Instrumented` wrapper. Read more
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#### fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current `Span`, returning an `Instrumented` wrapper. Read more
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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> IntoEither for T

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#### fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left` is `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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#### fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left(&self)` returns `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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### impl<T> Pointable for T

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#### const ALIGN: usize

The alignment of pointer.
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#### type Init = T

The type for initializers.
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#### unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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#### unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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#### unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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#### unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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### impl<T> Same for T

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#### type Output = T

Should always be `Self`
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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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### impl<I, T, U> Upcast<I, U> for T
where U: UpcastFrom<I, T>,

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#### fn upcast(self, interner: I) -> U

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### impl<I, T> UpcastFrom<I, T> for T

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#### fn upcast_from(from: T, _tcx: I) -> T

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### impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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#### fn vzip(self) -> V

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### impl<T> WithSubscriber for T

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#### fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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#### fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more

## Layout§

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.