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use core::ops::ControlFlow;
use rustc_hir as hir;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_middle::hir::map::Map;
use rustc_middle::hir::nested_filter;
use rustc_middle::middle::resolve_bound_vars as rbv;
use rustc_middle::ty::{self, Region, TyCtxt};
/// This function calls the `visit_ty` method for the parameters
/// corresponding to the anonymous regions. The `nested_visitor.found_type`
/// contains the anonymous type.
///
/// # Arguments
/// region - the anonymous region corresponding to the anon_anon conflict
/// br - the bound region corresponding to the above region which is of type `BrAnon(_)`
///
/// # Example
/// ```compile_fail
/// fn foo(x: &mut Vec<&u8>, y: &u8)
/// { x.push(y); }
/// ```
/// The function returns the nested type corresponding to the anonymous region
/// for e.g., `&u8` and `Vec<&u8>`.
pub fn find_anon_type<'tcx>(
tcx: TyCtxt<'tcx>,
generic_param_scope: LocalDefId,
region: Region<'tcx>,
br: &ty::BoundRegionKind,
) -> Option<(&'tcx hir::Ty<'tcx>, &'tcx hir::FnSig<'tcx>)> {
let anon_reg = tcx.is_suitable_region(generic_param_scope, region)?;
let fn_sig = tcx.hir_node_by_def_id(anon_reg.def_id).fn_sig()?;
fn_sig
.decl
.inputs
.iter()
.find_map(|arg| find_component_for_bound_region(tcx, arg, br))
.map(|ty| (ty, fn_sig))
}
// This method creates a FindNestedTypeVisitor which returns the type corresponding
// to the anonymous region.
fn find_component_for_bound_region<'tcx>(
tcx: TyCtxt<'tcx>,
arg: &'tcx hir::Ty<'tcx>,
br: &ty::BoundRegionKind,
) -> Option<&'tcx hir::Ty<'tcx>> {
FindNestedTypeVisitor { tcx, bound_region: *br, current_index: ty::INNERMOST }
.visit_ty(arg)
.break_value()
}
// The FindNestedTypeVisitor captures the corresponding `hir::Ty` of the
// anonymous region. The example above would lead to a conflict between
// the two anonymous lifetimes for &u8 in x and y respectively. This visitor
// would be invoked twice, once for each lifetime, and would
// walk the types like &mut Vec<&u8> and &u8 looking for the HIR
// where that lifetime appears. This allows us to highlight the
// specific part of the type in the error message.
struct FindNestedTypeVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
// The bound_region corresponding to the Refree(freeregion)
// associated with the anonymous region we are looking for.
bound_region: ty::BoundRegionKind,
current_index: ty::DebruijnIndex,
}
impl<'tcx> Visitor<'tcx> for FindNestedTypeVisitor<'tcx> {
type Result = ControlFlow<&'tcx hir::Ty<'tcx>>;
type NestedFilter = nested_filter::OnlyBodies;
fn nested_visit_map(&mut self) -> Self::Map {
self.tcx.hir()
}
fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) -> Self::Result {
match arg.kind {
hir::TyKind::BareFn(_) => {
self.current_index.shift_in(1);
intravisit::walk_ty(self, arg);
self.current_index.shift_out(1);
return ControlFlow::Continue(());
}
hir::TyKind::TraitObject(bounds, ..) => {
for bound in bounds {
self.current_index.shift_in(1);
self.visit_poly_trait_ref(bound);
self.current_index.shift_out(1);
}
}
hir::TyKind::Ref(lifetime, _) => {
// the lifetime of the Ref
let hir_id = lifetime.hir_id;
match (self.tcx.named_bound_var(hir_id), self.bound_region) {
// Find the index of the named region that was part of the
// error. We will then search the function parameters for a bound
// region at the right depth with the same index
(Some(rbv::ResolvedArg::EarlyBound(id)), ty::BrNamed(def_id, _)) => {
debug!("EarlyBound id={:?} def_id={:?}", id, def_id);
if id == def_id {
return ControlFlow::Break(arg);
}
}
// Find the index of the named region that was part of the
// error. We will then search the function parameters for a bound
// region at the right depth with the same index
(
Some(rbv::ResolvedArg::LateBound(debruijn_index, _, id)),
ty::BrNamed(def_id, _),
) => {
debug!(
"FindNestedTypeVisitor::visit_ty: LateBound depth = {:?}",
debruijn_index
);
debug!("LateBound id={:?} def_id={:?}", id, def_id);
if debruijn_index == self.current_index && id == def_id {
return ControlFlow::Break(arg);
}
}
(
Some(
rbv::ResolvedArg::StaticLifetime
| rbv::ResolvedArg::Free(_, _)
| rbv::ResolvedArg::EarlyBound(_)
| rbv::ResolvedArg::LateBound(_, _, _)
| rbv::ResolvedArg::Error(_),
)
| None,
_,
) => {
debug!("no arg found");
}
}
}
// Checks if it is of type `hir::TyKind::Path` which corresponds to a struct.
hir::TyKind::Path(_) => {
// Prefer using the lifetime in type arguments rather than lifetime arguments.
intravisit::walk_ty(self, arg)?;
// Call `walk_ty` as `visit_ty` is empty.
return if intravisit::walk_ty(
&mut TyPathVisitor {
tcx: self.tcx,
bound_region: self.bound_region,
current_index: self.current_index,
},
arg,
)
.is_break()
{
ControlFlow::Break(arg)
} else {
ControlFlow::Continue(())
};
}
_ => {}
}
// walk the embedded contents: e.g., if we are visiting `Vec<&Foo>`,
// go on to visit `&Foo`
intravisit::walk_ty(self, arg)
}
}
// The visitor captures the corresponding `hir::Ty` of the anonymous region
// in the case of structs ie. `hir::TyKind::Path`.
// This visitor would be invoked for each lifetime corresponding to a struct,
// and would walk the types like Vec<Ref> in the above example and Ref looking for the HIR
// where that lifetime appears. This allows us to highlight the
// specific part of the type in the error message.
struct TyPathVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
bound_region: ty::BoundRegionKind,
current_index: ty::DebruijnIndex,
}
impl<'tcx> Visitor<'tcx> for TyPathVisitor<'tcx> {
type Result = ControlFlow<()>;
type NestedFilter = nested_filter::OnlyBodies;
fn nested_visit_map(&mut self) -> Map<'tcx> {
self.tcx.hir()
}
fn visit_lifetime(&mut self, lifetime: &hir::Lifetime) -> Self::Result {
match (self.tcx.named_bound_var(lifetime.hir_id), self.bound_region) {
// the lifetime of the TyPath!
(Some(rbv::ResolvedArg::EarlyBound(id)), ty::BrNamed(def_id, _)) => {
debug!("EarlyBound id={:?} def_id={:?}", id, def_id);
if id == def_id {
return ControlFlow::Break(());
}
}
(Some(rbv::ResolvedArg::LateBound(debruijn_index, _, id)), ty::BrNamed(def_id, _)) => {
debug!("FindNestedTypeVisitor::visit_ty: LateBound depth = {:?}", debruijn_index,);
debug!("id={:?}", id);
debug!("def_id={:?}", def_id);
if debruijn_index == self.current_index && id == def_id {
return ControlFlow::Break(());
}
}
(
Some(
rbv::ResolvedArg::StaticLifetime
| rbv::ResolvedArg::EarlyBound(_)
| rbv::ResolvedArg::LateBound(_, _, _)
| rbv::ResolvedArg::Free(_, _)
| rbv::ResolvedArg::Error(_),
)
| None,
_,
) => {
debug!("no arg found");
}
}
ControlFlow::Continue(())
}
fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) -> Self::Result {
// ignore nested types
//
// If you have a type like `Foo<'a, &Ty>` we
// are only interested in the immediate lifetimes ('a).
//
// Making `visit_ty` empty will ignore the `&Ty` embedded
// inside, it will get reached by the outer visitor.
debug!("`Ty` corresponding to a struct is {:?}", arg);
ControlFlow::Continue(())
}
}