Struct rustc_hir_typeck::generator_interior::drop_ranges::cfg_build::DropRangeVisitor

struct DropRangeVisitor<'a, 'tcx> {
    typeck_results: &'a TypeckResults<'tcx>,
    infcx: &'a InferCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    places: ConsumedAndBorrowedPlaces,
    drop_ranges: DropRangesBuilder,
    expr_index: PostOrderId,
    label_stack: Vec<(Option<Label>, PostOrderId)>,
}

This struct is used to gather the information for DropRanges to determine the regions of the HIR tree for which a value is dropped.

We are interested in points where a variables is dropped or initialized, and the control flow of the code. We identify locations in code by their post-order traversal index, so it is important for this traversal to match that in RegionResolutionVisitor and InteriorVisitor.

We make several simplifying assumptions, with the goal of being more conservative than necessary rather than less conservative (since being less conservative is unsound, but more conservative is still safe). These assumptions are:

1. Moving a variable a counts as a move of the whole variable.
2. Moving a partial path like a.b.c is ignored.
3. Reinitializing through a field (e.g. a.b.c = 5) counts as a reinitialization of all of a.

Some examples:

Rule 1:

let mut a = (vec![0], vec![0]);
drop(a);
// `a` is not considered initialized.

Rule 2:

let mut a = (vec![0], vec![0]);
drop(a.0);
drop(a.1);
// `a` is still considered initialized.

Rule 3:

let mut a = (vec![0], vec![0]);
drop(a);
a.1 = vec![1];
// all of `a` is considered initialized

Fields

typeck_results: &'a TypeckResults<'tcx>

infcx: &'a InferCtxt<'tcx>

param_env: ParamEnv<'tcx>

places: ConsumedAndBorrowedPlaces

drop_ranges: DropRangesBuilder

expr_index: PostOrderId

label_stack: Vec<(Option<Label>, PostOrderId)>

Implementations

impl<'a, 'tcx> DropRangeVisitor<'a, 'tcx>

fn new( infcx: &'a InferCtxt<'tcx>, typeck_results: &'a TypeckResults<'tcx>, param_env: ParamEnv<'tcx>, places: ConsumedAndBorrowedPlaces, num_exprs: usize ) -> Self

fn tcx(&self) -> TyCtxt<'tcx>

fn record_drop(&mut self, value: TrackedValue)

fn consume_expr(&mut self, expr: &Expr<'_>)

ExprUseVisitor’s consume callback doesn’t go deep enough for our purposes in all expressions. This method consumes a little deeper into the expression when needed.

fn reinit_expr(&mut self, expr: &Expr<'_>)

Marks an expression as being reinitialized.

Note that we always approximated on the side of things being more initialized than they actually are, as opposed to less. In cases such as x.y = ..., we would consider all of x as being initialized instead of just the y field.

This is because it is always safe to consider something initialized even when it is not, but the other way around will cause problems.

In the future, we will hopefully tighten up these rules to be more precise.

fn handle_uninhabited_return(&mut self, expr: &Expr<'tcx>)

For an expression with an uninhabited return type (e.g. a function that returns !), this adds a self edge to the CFG to model the fact that the function does not return.

fn find_target_expression_from_destination( &self, destination: Destination ) -> Result<HirId, LoopIdError>

Map a Destination to an equivalent expression node

The destination field of a Break or Continue expression can target either an expression or a block. The drop range analysis, however, only deals in expression nodes, so blocks that might be the destination of a Break or Continue will not have a PostOrderId.

If the destination is an expression, this function will simply return that expression’s hir_id. If the destination is a block, this function will return the hir_id of last expression in the block.

Trait Implementations

impl<'a, 'tcx> Visitor<'tcx> for DropRangeVisitor<'a, 'tcx>

fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>)

fn visit_pat(&mut self, pat: &'tcx Pat<'tcx>)

type Map = <Self::NestedFilter as NestedFilter<'v>>::Map

type NestedFilter = None

Override this type to control which nested HIR are visited; see NestedFilter for details. If you override this type, you must also override nested_visit_map.

fn nested_visit_map(&mut self) -> Self::Map

If type NestedFilter is set to visit nested items, this method must also be overridden to provide a map to retrieve nested items.

fn visit_nested_item(&mut self, id: ItemId)

Invoked when a nested item is encountered. By default, when Self::NestedFilter is nested_filter::None, this method does nothing. You probably don’t want to override this method – instead, override Self::NestedFilter or use the “shallow” or “deep” visit patterns described on itemlikevisit::ItemLikeVisitor. The only reason to override this method is if you want a nested pattern but cannot supply a Map; see nested_visit_map for advice.

fn visit_nested_trait_item(&mut self, id: TraitItemId)

Like visit_nested_item(), but for trait items. See visit_nested_item() for advice on when to override this method.

fn visit_nested_impl_item(&mut self, id: ImplItemId)

Like visit_nested_item(), but for impl items. See visit_nested_item() for advice on when to override this method.

fn visit_nested_foreign_item(&mut self, id: ForeignItemId)

Like visit_nested_item(), but for foreign items. See visit_nested_item() for advice on when to override this method.

fn visit_nested_body(&mut self, id: BodyId)

Invoked to visit the body of a function, method or closure. Like visit_nested_item, does nothing by default unless you override Self::NestedFilter.

fn visit_param(&mut self, param: &'v Param<'v>)

fn visit_item(&mut self, i: &'v Item<'v>)

Visits the top-level item and (optionally) nested items / impl items. See visit_nested_item for details.

fn visit_body(&mut self, b: &'v Body<'v>)

fn visit_id(&mut self, _hir_id: HirId)

fn visit_name(&mut self, _name: Symbol)

fn visit_ident(&mut self, ident: Ident)

fn visit_mod(&mut self, m: &'v Mod<'v>, _s: Span, n: HirId)

fn visit_foreign_item(&mut self, i: &'v ForeignItem<'v>)

fn visit_local(&mut self, l: &'v Local<'v>)

fn visit_block(&mut self, b: &'v Block<'v>)

fn visit_stmt(&mut self, s: &'v Stmt<'v>)

fn visit_arm(&mut self, a: &'v Arm<'v>)

fn visit_pat_field(&mut self, f: &'v PatField<'v>)

fn visit_array_length(&mut self, len: &'v ArrayLen)

fn visit_anon_const(&mut self, c: &'v AnonConst)

fn visit_let_expr(&mut self, lex: &'v Let<'v>)

fn visit_expr_field(&mut self, field: &'v ExprField<'v>)

fn visit_ty(&mut self, t: &'v Ty<'v>)

fn visit_generic_param(&mut self, p: &'v GenericParam<'v>)

fn visit_const_param_default(&mut self, _param: HirId, ct: &'v AnonConst)

fn visit_generics(&mut self, g: &'v Generics<'v>)

fn visit_where_predicate(&mut self, predicate: &'v WherePredicate<'v>)

fn visit_fn_ret_ty(&mut self, ret_ty: &'v FnRetTy<'v>)

fn visit_fn_decl(&mut self, fd: &'v FnDecl<'v>)

fn visit_fn( &mut self, fk: FnKind<'v>, fd: &'v FnDecl<'v>, b: BodyId, _: Span, id: LocalDefId )

fn visit_use( &mut self, path: &'v Path<'v, SmallVec<[Res<HirId>; 3]>>, hir_id: HirId )

fn visit_trait_item(&mut self, ti: &'v TraitItem<'v>)

fn visit_trait_item_ref(&mut self, ii: &'v TraitItemRef)

fn visit_impl_item(&mut self, ii: &'v ImplItem<'v>)

fn visit_foreign_item_ref(&mut self, ii: &'v ForeignItemRef)

fn visit_impl_item_ref(&mut self, ii: &'v ImplItemRef)

fn visit_trait_ref(&mut self, t: &'v TraitRef<'v>)

fn visit_param_bound(&mut self, bounds: &'v GenericBound<'v>)

fn visit_poly_trait_ref(&mut self, t: &'v PolyTraitRef<'v>)

fn visit_variant_data(&mut self, s: &'v VariantData<'v>)

fn visit_field_def(&mut self, s: &'v FieldDef<'v>)

fn visit_enum_def(&mut self, enum_definition: &'v EnumDef<'v>, item_id: HirId)

fn visit_variant(&mut self, v: &'v Variant<'v>)

fn visit_label(&mut self, label: &'v Label)

fn visit_infer(&mut self, inf: &'v InferArg)

fn visit_generic_arg(&mut self, generic_arg: &'v GenericArg<'v>)

fn visit_lifetime(&mut self, lifetime: &'v Lifetime)

fn visit_qpath(&mut self, qpath: &'v QPath<'v>, id: HirId, _span: Span)

fn visit_path(&mut self, path: &Path<'v, Res<HirId>>, _id: HirId)

fn visit_path_segment(&mut self, path_segment: &'v PathSegment<'v>)

fn visit_generic_args(&mut self, generic_args: &'v GenericArgs<'v>)

fn visit_assoc_type_binding(&mut self, type_binding: &'v TypeBinding<'v>)

fn visit_attribute(&mut self, _attr: &'v Attribute)

fn visit_associated_item_kind(&mut self, kind: &'v AssocItemKind)

fn visit_defaultness(&mut self, defaultness: &'v Defaultness)

fn visit_inline_asm(&mut self, asm: &'v InlineAsm<'v>, id: HirId)

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:312 bytes