Struct rustc_middle::mir::LocalDecl

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,
}

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

impl<'tcx> LocalDecl<'tcx>

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

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) => ... }

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).

pub fn is_user_variable(&self) -> bool

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

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.

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.

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.

pub fn is_deref_temp(&self) -> bool

Returns true if this is a DerefTemp

pub fn from_compiler_desugaring(&self) -> bool

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

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

Creates a new LocalDecl for a temporary, mutable.

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

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

pub fn immutable(self) -> Self

Converts self into same LocalDecl except tagged as immutable.

Trait Implementations

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

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

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'tcx> Debug for LocalDecl<'tcx>

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

Formats the value using the given formatter.

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

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

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

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

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

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

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

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).

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.

impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for LocalDecl<'tcx>

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).

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