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use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use super::{FixupError, FixupResult, InferCtxt, Span};
use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFolder, TypeSuperFoldable};
use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitor};
use rustc_middle::ty::{self, Const, InferConst, Ty, TyCtxt, TypeFoldable, TypeVisitable};
use std::ops::ControlFlow;
///////////////////////////////////////////////////////////////////////////
// OPPORTUNISTIC VAR RESOLVER
/// The opportunistic resolver can be used at any time. It simply replaces
/// type/const variables that have been unified with the things they have
/// been unified with (similar to `shallow_resolve`, but deep). This is
/// useful for printing messages etc but also required at various
/// points for correctness.
pub struct OpportunisticVarResolver<'a, 'tcx> {
infcx: &'a InferCtxt<'tcx>,
}
impl<'a, 'tcx> OpportunisticVarResolver<'a, 'tcx> {
#[inline]
pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
OpportunisticVarResolver { infcx }
}
}
impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticVarResolver<'a, 'tcx> {
fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
if !t.has_non_region_infer() {
t // micro-optimize -- if there is nothing in this type that this fold affects...
} else {
let t = self.infcx.shallow_resolve(t);
t.super_fold_with(self)
}
}
fn fold_const(&mut self, ct: Const<'tcx>) -> Const<'tcx> {
if !ct.has_non_region_infer() {
ct // micro-optimize -- if there is nothing in this const that this fold affects...
} else {
let ct = self.infcx.shallow_resolve(ct);
ct.super_fold_with(self)
}
}
}
/// The opportunistic region resolver opportunistically resolves regions
/// variables to the variable with the least variable id. It is used when
/// normalizing projections to avoid hitting the recursion limit by creating
/// many versions of a predicate for types that in the end have to unify.
///
/// If you want to resolve type and const variables as well, call
/// [InferCtxt::resolve_vars_if_possible] first.
pub struct OpportunisticRegionResolver<'a, 'tcx> {
infcx: &'a InferCtxt<'tcx>,
}
impl<'a, 'tcx> OpportunisticRegionResolver<'a, 'tcx> {
pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
OpportunisticRegionResolver { infcx }
}
}
impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticRegionResolver<'a, 'tcx> {
fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
if !t.has_infer_regions() {
t // micro-optimize -- if there is nothing in this type that this fold affects...
} else {
t.super_fold_with(self)
}
}
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
match *r {
ty::ReVar(rid) => {
let resolved = self
.infcx
.inner
.borrow_mut()
.unwrap_region_constraints()
.opportunistic_resolve_var(rid);
TypeFolder::tcx(self).reuse_or_mk_region(r, ty::ReVar(resolved))
}
_ => r,
}
}
fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
if !ct.has_infer_regions() {
ct // micro-optimize -- if there is nothing in this const that this fold affects...
} else {
ct.super_fold_with(self)
}
}
}
///////////////////////////////////////////////////////////////////////////
// UNRESOLVED TYPE FINDER
/// The unresolved type **finder** walks a type searching for
/// type variables that don't yet have a value. The first unresolved type is stored.
/// It does not construct the fully resolved type (which might
/// involve some hashing and so forth).
pub struct UnresolvedTypeFinder<'a, 'tcx> {
infcx: &'a InferCtxt<'tcx>,
}
impl<'a, 'tcx> UnresolvedTypeFinder<'a, 'tcx> {
pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
UnresolvedTypeFinder { infcx }
}
}
impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'tcx> {
type BreakTy = (Ty<'tcx>, Option<Span>);
fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
let t = self.infcx.shallow_resolve(t);
if t.has_infer_types() {
if let ty::Infer(infer_ty) = *t.kind() {
// Since we called `shallow_resolve` above, this must
// be an (as yet...) unresolved inference variable.
let ty_var_span = if let ty::TyVar(ty_vid) = infer_ty {
let mut inner = self.infcx.inner.borrow_mut();
let ty_vars = &inner.type_variables();
if let TypeVariableOrigin {
kind: TypeVariableOriginKind::TypeParameterDefinition(_, _),
span,
} = *ty_vars.var_origin(ty_vid)
{
Some(span)
} else {
None
}
} else {
None
};
ControlFlow::Break((t, ty_var_span))
} else {
// Otherwise, visit its contents.
t.super_visit_with(self)
}
} else {
// All type variables in inference types must already be resolved,
// - no need to visit the contents, continue visiting.
ControlFlow::CONTINUE
}
}
}
///////////////////////////////////////////////////////////////////////////
// FULL TYPE RESOLUTION
/// Full type resolution replaces all type and region variables with
/// their concrete results. If any variable cannot be replaced (never unified, etc)
/// then an `Err` result is returned.
pub fn fully_resolve<'tcx, T>(infcx: &InferCtxt<'tcx>, value: T) -> FixupResult<'tcx, T>
where
T: TypeFoldable<'tcx>,
{
value.try_fold_with(&mut FullTypeResolver { infcx })
}
// N.B. This type is not public because the protocol around checking the
// `err` field is not enforceable otherwise.
struct FullTypeResolver<'a, 'tcx> {
infcx: &'a InferCtxt<'tcx>,
}
impl<'a, 'tcx> FallibleTypeFolder<'tcx> for FullTypeResolver<'a, 'tcx> {
type Error = FixupError<'tcx>;
fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
if !t.needs_infer() {
Ok(t) // micro-optimize -- if there is nothing in this type that this fold affects...
} else {
let t = self.infcx.shallow_resolve(t);
match *t.kind() {
ty::Infer(ty::TyVar(vid)) => Err(FixupError::UnresolvedTy(vid)),
ty::Infer(ty::IntVar(vid)) => Err(FixupError::UnresolvedIntTy(vid)),
ty::Infer(ty::FloatVar(vid)) => Err(FixupError::UnresolvedFloatTy(vid)),
ty::Infer(_) => {
bug!("Unexpected type in full type resolver: {:?}", t);
}
_ => t.try_super_fold_with(self),
}
}
}
fn try_fold_region(&mut self, r: ty::Region<'tcx>) -> Result<ty::Region<'tcx>, Self::Error> {
match *r {
ty::ReVar(_) => Ok(self
.infcx
.lexical_region_resolutions
.borrow()
.as_ref()
.expect("region resolution not performed")
.resolve_region(self.infcx.tcx, r)),
_ => Ok(r),
}
}
fn try_fold_const(&mut self, c: ty::Const<'tcx>) -> Result<ty::Const<'tcx>, Self::Error> {
if !c.needs_infer() {
Ok(c) // micro-optimize -- if there is nothing in this const that this fold affects...
} else {
let c = self.infcx.shallow_resolve(c);
match c.kind() {
ty::ConstKind::Infer(InferConst::Var(vid)) => {
return Err(FixupError::UnresolvedConst(vid));
}
ty::ConstKind::Infer(InferConst::Fresh(_)) => {
bug!("Unexpected const in full const resolver: {:?}", c);
}
_ => {}
}
c.try_super_fold_with(self)
}
}
}
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