Struct rustc_middle::middle::region::ScopeTree
source · pub struct ScopeTree {
pub root_body: Option<HirId>,
pub parent_map: FxIndexMap<Scope, (Scope, ScopeDepth)>,
var_map: FxIndexMap<ItemLocalId, Scope>,
destruction_scopes: FxIndexMap<ItemLocalId, Scope>,
pub rvalue_candidates: HirIdMap<RvalueCandidateType>,
pub yield_in_scope: FxHashMap<Scope, Vec<YieldData>>,
pub body_expr_count: FxHashMap<BodyId, usize>,
}
Expand description
The region scope tree encodes information about region relationships.
Fields§
§root_body: Option<HirId>
If not empty, this body is the root of this region hierarchy.
parent_map: FxIndexMap<Scope, (Scope, ScopeDepth)>
Maps from a scope ID to the enclosing scope id; this is usually corresponding to the lexical nesting, though in the case of closures the parent scope is the innermost conditional expression or repeating block. (Note that the enclosing scope ID for the block associated with a closure is the closure itself.)
var_map: FxIndexMap<ItemLocalId, Scope>
Maps from a variable or binding ID to the block in which that variable is declared.
destruction_scopes: FxIndexMap<ItemLocalId, Scope>
Maps from a NodeId
to the associated destruction scope (if any).
rvalue_candidates: HirIdMap<RvalueCandidateType>
Identifies expressions which, if captured into a temporary, ought to have a temporary whose lifetime extends to the end of the enclosing block, and not the enclosing statement. Expressions that are not present in this table are not rvalue candidates. The set of rvalue candidates is computed during type check based on a traversal of the AST.
yield_in_scope: FxHashMap<Scope, Vec<YieldData>>
If there are any yield
nested within a scope, this map
stores the Span
of the last one and its index in the
postorder of the Visitor traversal on the HIR.
HIR Visitor postorder indexes might seem like a peculiar thing to care about. but it turns out that HIR bindings and the temporary results of HIR expressions are never storage-live at the end of HIR nodes with postorder indexes lower than theirs, and therefore don’t need to be suspended at yield-points at these indexes.
For an example, suppose we have some code such as:
foo(f(), yield y, bar(g()))
With the HIR tree (calls numbered for expository purposes)
Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
Obviously, the result of f()
was created before the yield
(and therefore needs to be kept valid over the yield) while
the result of g()
occurs after the yield (and therefore
doesn’t). If we want to infer that, we can look at the
postorder traversal:
`foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
In which we can easily see that Call#1
occurs before the yield,
and Call#3
after it.
To see that this method works, consider:
Let D
be our binding/temporary and U
be our other HIR node, with
HIR-postorder(U) < HIR-postorder(D)
. Suppose, as in our example,
U is the yield and D is one of the calls.
Let’s show that D
is storage-dead at U
.
Remember that storage-live/storage-dead refers to the state of the storage, and does not consider moves/drop flags.
Then:
-
From the ordering guarantee of HIR visitors (see
rustc_hir::intravisit
),D
does not dominateU
. -
Therefore,
D
is potentially storage-dead atU
(because we might visitU
without ever getting toD
). -
However, we guarantee that at each HIR point, each binding/temporary is always either always storage-live or always storage-dead. This is what is being guaranteed by
terminating_scopes
including all blocks where the count of executions is not guaranteed. -
By
2.
and3.
,D
is statically storage-dead atU
, QED.
This property ought to not on (3) in an essential way – it is probably still correct even if we have “unrestricted” terminating scopes. However, why use the complicated proof when a simple one works?
A subtle thing: box
expressions, such as box (&x, yield 2, &y)
. It
might seem that a box
expression creates a Box<T>
temporary
when it starts executing, at HIR-preorder(BOX-EXPR)
. That might
be true in the MIR desugaring, but it is not important in the semantics.
The reason is that semantically, until the box
expression returns,
the values are still owned by their containing expressions. So
we’ll see that &x
.
body_expr_count: FxHashMap<BodyId, usize>
The number of visit_expr and visit_pat calls done in the body. Used to sanity check visit_expr/visit_pat call count when calculating generator interiors.
Implementations§
source§impl ScopeTree
impl ScopeTree
pub fn record_scope_parent( &mut self, child: Scope, parent: Option<(Scope, ScopeDepth)> )
pub fn opt_destruction_scope(&self, n: ItemLocalId) -> Option<Scope>
pub fn record_var_scope(&mut self, var: ItemLocalId, lifetime: Scope)
pub fn record_rvalue_candidate( &mut self, var: HirId, candidate_type: RvalueCandidateType )
sourcepub fn opt_encl_scope(&self, id: Scope) -> Option<Scope>
pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope>
Returns the narrowest scope that encloses id
, if any.
sourcepub fn var_scope(&self, var_id: ItemLocalId) -> Option<Scope>
pub fn var_scope(&self, var_id: ItemLocalId) -> Option<Scope>
Returns the lifetime of the local variable var_id
, if any.
sourcepub fn is_subscope_of(&self, subscope: Scope, superscope: Scope) -> bool
pub fn is_subscope_of(&self, subscope: Scope, superscope: Scope) -> bool
Returns true
if subscope
is equal to or is lexically nested inside superscope
, and
false
otherwise.
Used by clippy.
sourcepub fn yield_in_scope(&self, scope: Scope) -> Option<&[YieldData]>
pub fn yield_in_scope(&self, scope: Scope) -> Option<&[YieldData]>
Checks whether the given scope contains a yield
. If so,
returns Some(YieldData)
. If not, returns None
.
sourcepub fn body_expr_count(&self, body_id: BodyId) -> Option<usize>
pub fn body_expr_count(&self, body_id: BodyId) -> Option<usize>
Gives the number of expressions visited in a body. Used to sanity check visit_expr call count when calculating generator interiors.
Trait Implementations§
source§impl<'tcx> ArenaAllocatable<'tcx, IsNotCopy> for ScopeTree
impl<'tcx> ArenaAllocatable<'tcx, IsNotCopy> for ScopeTree
fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self
fn allocate_from_iter<'a>( arena: &'a Arena<'tcx>, iter: impl IntoIterator<Item = Self> ) -> &'a mut [Self]
source§impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree
impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree
fn hash_stable( &self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher )
Auto Trait Implementations§
impl RefUnwindSafe for ScopeTree
impl !Send for ScopeTree
impl !Sync for ScopeTree
impl Unpin for ScopeTree
impl UnwindSafe for ScopeTree
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T, R> CollectAndApply<T, R> for T
impl<T, R> CollectAndApply<T, R> for T
source§impl<Tcx, T> DepNodeParams<Tcx> for Twhere
Tcx: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
impl<Tcx, T> DepNodeParams<Tcx> for Twhere Tcx: DepContext, T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
default fn fingerprint_style() -> FingerprintStyle
source§default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint
default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint
default fn to_debug_str(&self, _: Tcx) -> String
source§default fn recover(_: Tcx, _: &DepNode) -> Option<T>
default fn recover(_: Tcx, _: &DepNode) -> Option<T>
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.source§impl<P> IntoQueryParam<P> for P
impl<P> IntoQueryParam<P> for P
fn into_query_param(self) -> P
source§impl<T> MaybeResult<T> for T
impl<T> MaybeResult<T> for T
source§impl<'tcx, T> ToPredicate<'tcx, T> for T
impl<'tcx, T> ToPredicate<'tcx, T> for T
fn to_predicate(self, _tcx: TyCtxt<'tcx>) -> T
source§impl<Tcx, T> Value<Tcx> for Twhere
Tcx: DepContext,
impl<Tcx, T> Value<Tcx> for Twhere Tcx: DepContext,
default fn from_cycle_error( tcx: Tcx, cycle: &[QueryInfo], _guar: ErrorGuaranteed ) -> T
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: 296 bytes