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Mar 7, 2023
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infer: fix and improve comments #108728

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61 changes: 32 additions & 29 deletions compiler/rustc_infer/src/infer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -114,24 +114,26 @@ pub struct InferCtxtInner<'tcx> {
float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>,

/// Tracks the set of region variables and the constraints between them.
///
/// This is initially `Some(_)` but when
/// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
/// -- further attempts to perform unification, etc., may fail if new
/// region constraints would've been added.
region_constraint_storage: Option<RegionConstraintStorage<'tcx>>,

/// A set of constraints that regionck must validate. Each
/// constraint has the form `T:'a`, meaning "some type `T` must
/// A set of constraints that regionck must validate.
///
/// Each constraint has the form `T:'a`, meaning "some type `T` must
/// outlive the lifetime 'a". These constraints derive from
/// instantiated type parameters. So if you had a struct defined
/// like
/// like the following:
/// ```ignore (illustrative)
/// struct Foo<T:'static> { ... }
/// struct Foo<T: 'static> { ... }
/// ```
/// then in some expression `let x = Foo { ... }` it will
/// In some expression `let x = Foo { ... }`, it will
/// instantiate the type parameter `T` with a fresh type `$0`. At
/// the same time, it will record a region obligation of
/// `$0:'static`. This will get checked later by regionck. (We
/// `$0: 'static`. This will get checked later by regionck. (We
/// can't generally check these things right away because we have
/// to wait until types are resolved.)
///
Expand Down Expand Up @@ -268,7 +270,7 @@ pub struct InferCtxt<'tcx> {
/// Caches the results of trait evaluation.
pub evaluation_cache: select::EvaluationCache<'tcx>,

/// the set of predicates on which errors have been reported, to
/// The set of predicates on which errors have been reported, to
/// avoid reporting the same error twice.
pub reported_trait_errors: RefCell<FxIndexMap<Span, Vec<ty::Predicate<'tcx>>>>,

Expand All @@ -291,7 +293,7 @@ pub struct InferCtxt<'tcx> {
tainted_by_errors: Cell<Option<ErrorGuaranteed>>,

/// Track how many errors were reported when this infcx is created.
/// If the number of errors increases, that's also a sign (line
/// If the number of errors increases, that's also a sign (like
/// `tainted_by_errors`) to avoid reporting certain kinds of errors.
// FIXME(matthewjasper) Merge into `tainted_by_errors`
err_count_on_creation: usize,
Expand All @@ -313,7 +315,7 @@ pub struct InferCtxt<'tcx> {
/// During coherence we have to assume that other crates may add
/// additional impls which we currently don't know about.
///
/// To deal with this evaluation should be conservative
/// To deal with this evaluation, we should be conservative
/// and consider the possibility of impls from outside this crate.
/// This comes up primarily when resolving ambiguity. Imagine
/// there is some trait reference `$0: Bar` where `$0` is an
Expand All @@ -323,7 +325,7 @@ pub struct InferCtxt<'tcx> {
/// bound to some type that in a downstream crate that implements
/// `Bar`.
///
/// Outside of coherence we set this to false because we are only
/// Outside of coherence, we set this to false because we are only
/// interested in types that the user could actually have written.
/// In other words, we consider `$0: Bar` to be unimplemented if
/// there is no type that the user could *actually name* that
Expand Down Expand Up @@ -373,7 +375,7 @@ pub enum SubregionOrigin<'tcx> {
Subtype(Box<TypeTrace<'tcx>>),

/// When casting `&'a T` to an `&'b Trait` object,
/// relating `'a` to `'b`
/// relating `'a` to `'b`.
RelateObjectBound(Span),

/// Some type parameter was instantiated with the given type,
Expand All @@ -384,7 +386,7 @@ pub enum SubregionOrigin<'tcx> {
/// that must outlive some other region.
RelateRegionParamBound(Span),

/// Creating a pointer `b` to contents of another reference
/// Creating a pointer `b` to contents of another reference.
Reborrow(Span),

/// (&'a &'b T) where a >= b
Expand All @@ -398,7 +400,7 @@ pub enum SubregionOrigin<'tcx> {
trait_item_def_id: DefId,
},

/// Checking that the bounds of a trait's associated type hold for a given impl
/// Checking that the bounds of a trait's associated type hold for a given impl.
CheckAssociatedTypeBounds {
parent: Box<SubregionOrigin<'tcx>>,
impl_item_def_id: LocalDefId,
Expand Down Expand Up @@ -435,32 +437,33 @@ pub enum LateBoundRegionConversionTime {
AssocTypeProjection(DefId),
}

/// Reasons to create a region inference variable
/// Reasons to create a region inference variable.
///
/// See `error_reporting` module for more details
/// See `error_reporting` module for more details.
#[derive(Copy, Clone, Debug)]
pub enum RegionVariableOrigin {
/// Region variables created for ill-categorized reasons,
/// mostly indicates places in need of refactoring
/// Region variables created for ill-categorized reasons.
///
/// They mostly indicate places in need of refactoring.
MiscVariable(Span),

/// Regions created by a `&P` or `[...]` pattern
/// Regions created by a `&P` or `[...]` pattern.
PatternRegion(Span),

/// Regions created by `&` operator
/// Regions created by `&` operator.
///
AddrOfRegion(Span),

/// Regions created as part of an autoref of a method receiver
/// Regions created as part of an autoref of a method receiver.
Autoref(Span),

/// Regions created as part of an automatic coercion
/// Regions created as part of an automatic coercion.
Coercion(Span),

/// Region variables created as the values for early-bound regions
/// Region variables created as the values for early-bound regions.
EarlyBoundRegion(Span, Symbol),

/// Region variables created for bound regions
/// in a function or method that is called
/// in a function or method that is called.
LateBoundRegion(Span, ty::BoundRegionKind, LateBoundRegionConversionTime),

UpvarRegion(ty::UpvarId, Span),
Expand Down Expand Up @@ -534,7 +537,7 @@ impl<'tcx> fmt::Display for FixupError<'tcx> {
}
}

/// Used to configure inference contexts before their creation
/// Used to configure inference contexts before their creation.
pub struct InferCtxtBuilder<'tcx> {
tcx: TyCtxt<'tcx>,
defining_use_anchor: DefiningAnchor,
Expand Down Expand Up @@ -835,9 +838,9 @@ impl<'tcx> InferCtxt<'tcx> {

/// Scan the constraints produced since `snapshot` began and returns:
///
/// - `None` -- if none of them involve "region outlives" constraints
/// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
/// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
/// - `None` -- if none of them involves "region outlives" constraints.
/// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder.
/// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders.
pub fn region_constraints_added_in_snapshot(
&self,
snapshot: &CombinedSnapshot<'tcx>,
Expand Down Expand Up @@ -1770,7 +1773,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
}
}

/// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
/// Helper for [InferCtxt::ty_or_const_infer_var_changed] (see comment on that), currently
/// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
#[derive(Copy, Clone, Debug)]
pub enum TyOrConstInferVar<'tcx> {
Expand Down