# Struct rustc_middle::mir::LocalDecl

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    pub struct LocalDecl<'tcx> {
        pub mutability: Mutability,
        pub local_info: ClearCrossCrate<Box<LocalInfo<'tcx>>>,
        pub ty: Ty<'tcx>,
        pub user_ty: Option<Box<UserTypeProjections>>,
        pub source_info: SourceInfo,
    }

Expand description

A MIR local.

This can be a binding declared by the user, a temporary inserted by the compiler, a function argument, or the return place.

## Fields§

§`mutability: Mutability`

Whether this is a mutable binding (i.e., `let x` or `let mut x`).

Temporaries and the return place are always mutable.

§`local_info: ClearCrossCrate<Box<LocalInfo<'tcx>>>`§`ty: Ty<'tcx>`

The type of this local.

§`user_ty: Option<Box<UserTypeProjections>>`

If the user manually ascribed a type to this variable, e.g., via `let x: T`, then we carry that type here. The MIR borrow checker needs this information since it can affect region inference.

§`source_info: SourceInfo`

The syntactic (i.e., not visibility) source scope the local is defined in. If the local was defined in a let-statement, this is within the let-statement, rather than outside of it.

This is needed because the visibility source scope of locals within a let-statement is weird.

The reason is that we want the local to be within the let-statement for lint purposes, but we want the local to be after the let-statement for names-in-scope purposes.

That’s it, if we have a let-statement like the one in this function:

    fn foo(x: &str) {
        #[allow(unused_mut)]
        let mut x: u32 = { // <- one unused mut
            let mut y: u32 = x.parse().unwrap();
            y + 2
        };
        drop(x);
    }

Then, from a lint point of view, the declaration of `x: u32` (and `y: u32`) are within the `#[allow(unused_mut)]` scope - the lint scopes are the same as the AST/HIR nesting.

However, from a name lookup point of view, the scopes look more like as if the let-statements were `match` expressions:

    fn foo(x: &str) {
        match {
            match x.parse::<u32>().unwrap() {
                y => y + 2
            }
        } {
            x => drop(x)
        };
    }

We care about the name-lookup scopes for debuginfo - if the debuginfo instruction pointer is at the call to `x.parse()`, we want `x` to refer to `x: &str`, but if it is at the call to `drop(x)`, we want it to refer to `x: u32`.

To allow both uses to work, we need to have more than a single scope for a local. We have the `source_info.scope` represent the “syntactic” lint scope (with a variable being under its let block) while the `var_debug_info.source_info.scope` represents the “local variable” scope (where the “rest” of a block is under all prior let-statements).

The end result looks like this:

    ROOT SCOPE
     │{ argument x: &str }
     │
     │ │{ #[allow(unused_mut)] } // This is actually split into 2 scopes
     │ │                         // in practice because I'm lazy.
     │ │
     │ │← x.source_info.scope
     │ │← `x.parse().unwrap()`
     │ │
     │ │ │← y.source_info.scope
     │ │
     │ │ │{ let y: u32 }
     │ │ │
     │ │ │← y.var_debug_info.source_info.scope
     │ │ │← `y + 2`
     │
     │ │{ let x: u32 }
     │ │← x.var_debug_info.source_info.scope
     │ │← `drop(x)` // This accesses `x: u32`.

## Implementations§

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### impl<'tcx> LocalDecl<'tcx>

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#### pub fn local_info(&self) -> &LocalInfo<'tcx>

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

Returns `true` only if local is a binding that can itself be made mutable via the addition of the `mut` keyword, namely something like the occurrences of `x` in:

- `fn foo(x: Type) { ... }`,
- `let x = ...`,
- or `match ... { C(x) => ... }`

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

Returns `true` if local is definitely not a `ref ident` or `ref mut ident` binding. (Such bindings cannot be made into mutable bindings, but the inverse does not necessarily hold).

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

Returns `true` if this variable is a named variable or function parameter declared by the user.

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

Returns `true` if this is a reference to a variable bound in a `match` expression that is used to access said variable for the guard of the match arm.

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

Returns `Some` if this is a reference to a static item that is used to access that static.

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

Returns `Some` if this is a reference to a thread-local static item that is used to access that static.

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

Returns `true` if this is a DerefTemp

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

Returns `true` is the local is from a compiler desugaring, e.g., `__next` from a `for` loop.

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#### pub fn new(ty: Ty<'tcx>, span: Span) -> Self

Creates a new `LocalDecl` for a temporary, mutable.

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#### pub fn with_source_info(ty: Ty<'tcx>, source_info: SourceInfo) -> Self

Like `LocalDecl::new`, but takes a `SourceInfo` instead of a `Span`.

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#### pub fn immutable(self) -> Self

Converts `self` into same `LocalDecl` except tagged as immutable.

## Trait Implementations§

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### impl<'tcx> Clone for LocalDecl<'tcx>

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#### fn clone(&self) -> LocalDecl<'tcx>

Returns a copy 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<'tcx> Debug for LocalDecl<'tcx>

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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<'tcx, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for LocalDecl<'tcx>

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

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### impl<'tcx, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for LocalDecl<'tcx>

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

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### impl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for LocalDecl<'tcx>

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#### fn hash_stable( &self, __hcx: &mut StableHashingContext<'__ctx>, __hasher: &mut StableHasher )

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### impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for LocalDecl<'tcx>

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#### fn try_fold_with<__F: FallibleTypeFolder<TyCtxt<'tcx>>>( self, __folder: &mut __F ) -> Result<Self, __F::Error>

The entry point for folding. To fold a value `t` with a folder `f` call: `t.try_fold_with(f)`. Read more
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#### fn fold_with<F>(self, folder: &mut F) -> Self
where F: TypeFolder<I>,

A convenient alternative to `try_fold_with` for use with infallible folders. Do not override this method, to ensure coherence with `try_fold_with`.
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### impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for LocalDecl<'tcx>

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#### fn visit_with<__V: TypeVisitor<TyCtxt<'tcx>>>( &self, __visitor: &mut __V ) -> __V::Result

The entry point for visiting. To visit a value `t` with a visitor `v` call: `t.visit_with(v)`. Read more

## Auto Trait Implementations§

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### impl<'tcx> DynSend for LocalDecl<'tcx>

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### impl<'tcx> DynSync for LocalDecl<'tcx>

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### impl<'tcx> Freeze for LocalDecl<'tcx>

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### impl<'tcx> !RefUnwindSafe for LocalDecl<'tcx>

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### impl<'tcx> Send for LocalDecl<'tcx>

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### impl<'tcx> Sync for LocalDecl<'tcx>

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### impl<'tcx> Unpin for LocalDecl<'tcx>

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### impl<'tcx> !UnwindSafe for LocalDecl<'tcx>

## 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, 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<Tcx, T> DepNodeParams<Tcx> for T
where Tcx: DepContext, T: for<'a> HashStable<StableHashingContext<'a>> + Debug,

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#### default fn fingerprint_style() -> FingerprintStyle

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#### default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint

This method turns the parameters of a DepNodeConstructor into an opaque Fingerprint to be used in DepNode. Not all DepNodeParams support being turned into a Fingerprint (they don’t need to if the corresponding DepNode is anonymous).
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#### default fn to_debug_str(&self, _: Tcx) -> String

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#### default fn recover(_: Tcx, _: &DepNode) -> Option<T>

This method tries to recover the query key from the given `DepNode`, something which is needed when forcing `DepNode`s during red-green evaluation. The query system will only call this method if `fingerprint_style()` is not `FingerprintStyle::Opaque`. It is always valid to return `None` here, in which case incremental compilation will treat the query as having changed instead of forcing it.
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### impl<T> Filterable for T

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#### fn filterable( self, filter_name: &'static str ) -> RequestFilterDataProvider<T, fn(_: DataRequest<'_>) -> bool>

Creates a filterable data provider with the given name for debugging. Read more
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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<P> IntoQueryParam<P> for P

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#### fn into_query_param(self) -> P

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### impl<'tcx, T> IsSuggestable<'tcx> for T
where T: TypeVisitable<TyCtxt<'tcx>> + TypeFoldable<TyCtxt<'tcx>>,

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#### fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool

Whether this makes sense to suggest in a diagnostic. Read more
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#### fn make_suggestable( self, tcx: TyCtxt<'tcx>, infer_suggestable: bool ) -> Option<T>

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### impl<T> MaybeResult<T> for T

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#### type Error = !

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#### fn from(_: Result<T, <T as MaybeResult<T>>::Error>) -> T

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#### fn to_result(self) -> Result<T, <T as MaybeResult<T>>::Error>

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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<'tcx, T> ToPredicate<'tcx, T> for T

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#### fn to_predicate(self, _tcx: TyCtxt<'tcx>) -> T

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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> TypeVisitableExt<I> for T
where I: Interner, T: TypeVisitable<I>,

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#### fn has_type_flags(&self, flags: TypeFlags) -> bool

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#### fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool

Returns `true` if `self` has any late-bound regions that are either bound by `binder` or bound by some binder outside of `binder`. If `binder` is `ty::INNERMOST`, this indicates whether there are any late-bound regions that appear free.
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#### fn error_reported(&self) -> Result<(), <I as Interner>::ErrorGuaranteed>

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#### fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool

Returns `true` if this type has any regions that escape `binder` (and hence are not bound by it).
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#### fn has_escaping_bound_vars(&self) -> bool

Return `true` if this type has regions that are not a part of the type. For example, `for<'a> fn(&'a i32)` return `false`, while `fn(&'a i32)` would return `true`. The latter can occur when traversing through the former. Read more
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#### fn has_projections(&self) -> bool

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#### fn has_inherent_projections(&self) -> bool

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#### fn has_opaque_types(&self) -> bool

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#### fn has_coroutines(&self) -> bool

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#### fn references_error(&self) -> bool

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#### fn has_non_region_param(&self) -> bool

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#### fn has_infer_regions(&self) -> bool

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#### fn has_infer_types(&self) -> bool

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#### fn has_non_region_infer(&self) -> bool

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#### fn has_infer(&self) -> bool

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#### fn has_placeholders(&self) -> bool

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#### fn has_non_region_placeholders(&self) -> bool

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#### fn has_param(&self) -> bool

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#### fn has_free_regions(&self) -> bool

“Free” regions in this context means that it has any region that is not (a) erased or (b) late-bound.
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#### fn has_erased_regions(&self) -> bool

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#### fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.
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#### fn is_global(&self) -> bool

Indicates whether this value references only ‘global’ generic parameters that are the same regardless of what fn we are in. This is used for caching.
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#### fn has_bound_regions(&self) -> bool

True if there are any late-bound regions
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#### fn has_non_region_bound_vars(&self) -> bool

True if there are any late-bound non-region variables
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#### fn has_bound_vars(&self) -> bool

True if there are any bound variables
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#### fn still_further_specializable(&self) -> bool

Indicates whether this value still has parameters/placeholders/inference variables which could be replaced later, in a way that would change the results of `impl` specialization.
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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<Tcx, T> Value<Tcx> for T
where Tcx: DepContext,

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#### default fn from_cycle_error( tcx: Tcx, cycle_error: &CycleError, _guar: ErrorGuaranteed ) -> T

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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
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### impl<'a, T> Captures<'a> for T
where T: ?Sized,

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

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### impl<T> MaybeSendSync for T
where T: Send + Sync,

## 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: 40 bytes