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[draft] Revised approach to backport of PR #96970 #97036

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[draft] Revised approach to backport of PR #96970 #97036

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4d7a21d
A revised, beta-targeted, approach to PR 96970.
pnkfelix May 14, 2022
28c24cc
result of blessing the ui tests. I skimmed these results and compared…
pnkfelix May 14, 2022
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7 changes: 6 additions & 1 deletion compiler/rustc_ast_lowering/src/item.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,8 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
lifetimes_to_define: Vec::new(),
is_collecting_anonymous_lifetimes: None,
in_scope_lifetimes: Vec::new(),
hkt_bound_lifetimes: Vec::new(),

allow_try_trait: Some([sym::try_trait_v2][..].into()),
allow_gen_future: Some([sym::gen_future][..].into()),
allow_into_future: Some([sym::into_future][..].into()),
Expand Down Expand Up @@ -1537,7 +1539,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
span,
}) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
span: self.lower_span(span),
lifetime: self.lower_lifetime(lifetime),
lifetime: self.lower_lifetime(
lifetime,
ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
),
bounds: self.lower_param_bounds(
bounds,
ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
Expand Down
130 changes: 107 additions & 23 deletions compiler/rustc_ast_lowering/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,9 @@ mod path;

rustc_hir::arena_types!(rustc_arena::declare_arena);

#[allow(non_camel_case_types)]
type usize_nesting = u32;

struct LoweringContext<'a, 'hir: 'a> {
/// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
sess: &'a Session,
Expand Down Expand Up @@ -144,6 +147,10 @@ struct LoweringContext<'a, 'hir: 'a> {
/// vector.
in_scope_lifetimes: Vec<ParamName>,

/// `for<'a>` bound lifetimes currently in scope, and the
/// ReturnPositionOpaqueTy-depth they were bound at.
hkt_bound_lifetimes: Vec<(hir::LifetimeName, Span, usize_nesting)>,

current_hir_id_owner: LocalDefId,
item_local_id_counter: hir::ItemLocalId,
local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
Expand Down Expand Up @@ -222,6 +229,9 @@ enum ImplTraitContext<'b, 'a> {
fn_def_id: LocalDefId,
/// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
origin: hir::OpaqueTyOrigin,
/// The depth to which we have nested return position opaque types.
/// 0 if the context *is* is the outermost return position opaque type.
nested: usize_nesting,
},
/// Impl trait in type aliases.
TypeAliasesOpaqueTy {
Expand Down Expand Up @@ -273,8 +283,8 @@ impl<'a> ImplTraitContext<'_, 'a> {
use self::ImplTraitContext::*;
match self {
Universal(params, parent) => Universal(params, *parent),
ReturnPositionOpaqueTy { fn_def_id, origin } => {
ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
ReturnPositionOpaqueTy { fn_def_id, origin, nested } => {
ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin, nested: *nested }
}
TypeAliasesOpaqueTy { capturable_lifetimes } => {
TypeAliasesOpaqueTy { capturable_lifetimes }
Expand Down Expand Up @@ -1162,7 +1172,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericArg<'hir> {
match arg {
ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(&lt)),
ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(&lt, itctx)),
ast::GenericArg::Type(ty) => {
match ty.kind {
TyKind::Infer if self.sess.features_untracked().generic_arg_infer => {
Expand Down Expand Up @@ -1260,10 +1270,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
TyKind::Rptr(ref region, ref mt) => {
let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
let lifetime = match *region {
Some(ref lt) => self.lower_lifetime(lt),
Some(ref lt) => self.lower_lifetime(lt, itctx.reborrow()),
None => self.elided_ref_lifetime(span),
};
hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx.reborrow()))
}
TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
Expand Down Expand Up @@ -1327,7 +1337,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
) => None,
GenericBound::Outlives(ref lifetime) => {
if lifetime_bound.is_none() {
lifetime_bound = Some(this.lower_lifetime(lifetime));
lifetime_bound =
Some(this.lower_lifetime(lifetime, itctx.reborrow()));
}
None
}
Expand All @@ -1342,15 +1353,23 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
TyKind::ImplTrait(def_node_id, ref bounds) => {
let span = t.span;
match itctx {
ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self
.lower_opaque_impl_trait(
ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin, nested } => {
self.lower_opaque_impl_trait(
span,
Some(fn_def_id),
origin,
def_node_id,
None,
|this| this.lower_param_bounds(bounds, itctx),
),
|this, itctx| this.lower_param_bounds(bounds, itctx),
ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id,
origin,
nested: nested.checked_add(1).unwrap_or_else(|| {
panic!("return position opaque ty nesting depth exceeded max");
})
},
)
}
ImplTraitContext::TypeAliasesOpaqueTy { ref capturable_lifetimes } => {
// Reset capturable lifetimes, any nested impl trait
// types will inherit lifetimes from this opaque type,
Expand All @@ -1364,7 +1383,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
hir::OpaqueTyOrigin::TyAlias,
def_node_id,
Some(capturable_lifetimes),
|this| this.lower_param_bounds(bounds, nested_itctx),
|this, itctx| this.lower_param_bounds(bounds, itctx),
nested_itctx,
)
}
ImplTraitContext::Universal(in_band_ty_params, parent_def_id) => {
Expand Down Expand Up @@ -1428,7 +1448,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
origin: hir::OpaqueTyOrigin,
opaque_ty_node_id: NodeId,
capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
lower_bounds: impl FnOnce(&mut Self, ImplTraitContext<'_, 'hir>) -> hir::GenericBounds<'hir>,
mut itctx: ImplTraitContext<'_, 'hir>,
) -> hir::TyKind<'hir> {
debug!(
"lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
Expand All @@ -1446,7 +1467,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {

let mut collected_lifetimes = Vec::new();
self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
let hir_bounds = lower_bounds(lctx);
let hir_bounds = lower_bounds(lctx, itctx.reborrow());

collected_lifetimes = lifetimes_from_impl_trait_bounds(
opaque_ty_node_id,
Expand Down Expand Up @@ -1636,6 +1657,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id: def_id,
origin: hir::OpaqueTyOrigin::FnReturn(def_id),
nested: 0,
}
}
_ => ImplTraitContext::Disallowed(match kind {
Expand Down Expand Up @@ -1907,6 +1929,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
let context = ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id,
origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
nested: 0,
};
self.lower_ty(ty, context)
}
Expand All @@ -1933,40 +1956,40 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
fn lower_param_bound(
&mut self,
tpb: &GenericBound,
itctx: ImplTraitContext<'_, 'hir>,
mut itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericBound<'hir> {
match tpb {
GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
self.lower_poly_trait_ref(p, itctx),
self.lower_trait_bound_modifier(*modifier),
),
GenericBound::Outlives(lifetime) => {
hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
hir::GenericBound::Outlives(self.lower_lifetime(lifetime, itctx.reborrow()))
}
}
}

fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
fn lower_lifetime(&mut self, l: &Lifetime, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Lifetime {
let span = self.lower_span(l.ident.span);
match l.ident {
ident if ident.name == kw::StaticLifetime => {
self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
self.new_named_lifetime(l.id, span, hir::LifetimeName::Static, itctx.reborrow())
}
ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
AnonymousLifetimeMode::CreateParameter => {
let fresh_name = self.collect_fresh_anonymous_lifetime(span);
self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name), itctx.reborrow())
}

AnonymousLifetimeMode::PassThrough => {
self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore, itctx.reborrow())
}

AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
},
ident => {
let param_name = ParamName::Plain(self.lower_ident(ident));
self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name), itctx.reborrow())
}
}
}
Expand All @@ -1976,7 +1999,57 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
id: NodeId,
span: Span,
name: hir::LifetimeName,
mut itctx: ImplTraitContext<'_, 'hir>,
) -> hir::Lifetime {
fn check_impl_trait_lifetimes(
sess: &Session,
itctx: ImplTraitContext<'_, '_>,
span: Span,
note_span: Option<Span>,
def_site_nesting: usize_nesting,
) {
match itctx {
ImplTraitContext::ReturnPositionOpaqueTy { nested, .. }
if nested > 0 && nested > def_site_nesting =>
{
debug!("check_impl_trait_lifetimes badness \
nested: {} def_site_nesting: {}, span: {:?}, note_span: {:?}",
nested, def_site_nesting, span, note_span);
// fall through to error reporting code
}
ImplTraitContext::TypeAliasesOpaqueTy { .. } => {
// fall through to error reporting code
}
_ => {
// otherwise, accept this lifetime
return
}
}
let mut err = sess.struct_span_err(
span,
"higher kinded lifetime bounds on nested opaque types are not supported yet",
);
if let Some(span) = note_span {
err.span_note(span, "lifetime declared here");
}
err.help(
"See https://github.com/rust-lang/rust/issues/96194 for further details",
);
err.emit();
}

for (lt, def_site_span, def_site_nesting) in &self.hkt_bound_lifetimes {
if lt == &name {
check_impl_trait_lifetimes(
self.sess,
itctx.reborrow(),
span,
Some(*def_site_span),
*def_site_nesting,
);
}
}

hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
}

Expand Down Expand Up @@ -2013,7 +2086,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {

let lt = self
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident }, itctx.reborrow())
});
let param_name = match lt.name {
hir::LifetimeName::Param(param_name) => param_name,
Expand Down Expand Up @@ -2108,8 +2181,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
capturable_lifetimes.extend(lt_def_names.clone());
}

let hkt_len = this.hkt_bound_lifetimes.len();
if let ImplTraitContext::ReturnPositionOpaqueTy { nested: rp_nesting, .. } = itctx {
this.hkt_bound_lifetimes.extend(lt_def_names.clone().map(|lt| (lt, p.span, rp_nesting)));
}

let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());

this.hkt_bound_lifetimes.truncate(hkt_len);
if let ImplTraitContext::TypeAliasesOpaqueTy { ref mut capturable_lifetimes } = itctx {
for param in lt_def_names {
capturable_lifetimes.remove(&param);
Expand Down Expand Up @@ -2418,7 +2497,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
err.span_label(span, label);
err.emit();

self.new_named_lifetime(id, span, hir::LifetimeName::Error)
self.new_silent_error_lifetime(id, span)
}

fn new_silent_error_lifetime(&mut self, id: NodeId, span: Span) -> hir::Lifetime
{
hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name: hir::LifetimeName::Error }
}

/// Invoked to create the lifetime argument(s) for a path like
Expand All @@ -2441,7 +2525,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
self.sess
.delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
let id = self.resolver.next_node_id();
self.new_named_lifetime(id, span, hir::LifetimeName::Error)
self.new_silent_error_lifetime(id, span)
}
// `PassThrough` is the normal case.
// `new_error_lifetime`, which would usually be used in the case of `ReportError`,
Expand Down
6 changes: 4 additions & 2 deletions src/test/ui/error-codes/E0657.rs
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Expand Up @@ -8,7 +8,8 @@ impl<T> Id<T> for T {}

fn free_fn_capture_hrtb_in_impl_trait()
-> Box<for<'a> Id<impl Lt<'a>>>
//~^ ERROR `impl Trait` can only capture lifetimes bound at the fn or impl level [E0657]
//~^ ERROR `impl Trait` can only capture lifetimes bound at the fn or impl level [E0657]
//~| ERROR lifetime bounds on nested opaque types are not supported yet
{
Box::new(())
}
Expand All @@ -17,7 +18,8 @@ struct Foo;
impl Foo {
fn impl_fn_capture_hrtb_in_impl_trait()
-> Box<for<'a> Id<impl Lt<'a>>>
//~^ ERROR `impl Trait` can only capture lifetimes bound at the fn or impl level
//~^ ERROR `impl Trait` can only capture lifetimes bound at the fn or impl level
//~| ERROR lifetime bounds on nested opaque types are not supported yet
{
Box::new(())
}
Expand Down
30 changes: 28 additions & 2 deletions src/test/ui/error-codes/E0657.stderr
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Original file line number Diff line number Diff line change
@@ -1,15 +1,41 @@
error: higher kinded lifetime bounds on nested opaque types are not supported yet
--> $DIR/E0657.rs:10:31
|
LL | -> Box<for<'a> Id<impl Lt<'a>>>
| ^^
|
note: lifetime declared here
--> $DIR/E0657.rs:10:12
|
LL | -> Box<for<'a> Id<impl Lt<'a>>>
| ^^^^^^^^^^^^^^^^^^^^^^^
= help: See https://github.com/rust-lang/rust/issues/96194 for further details

error: higher kinded lifetime bounds on nested opaque types are not supported yet
--> $DIR/E0657.rs:20:35
|
LL | -> Box<for<'a> Id<impl Lt<'a>>>
| ^^
|
note: lifetime declared here
--> $DIR/E0657.rs:20:16
|
LL | -> Box<for<'a> Id<impl Lt<'a>>>
| ^^^^^^^^^^^^^^^^^^^^^^^
= help: See https://github.com/rust-lang/rust/issues/96194 for further details

error[E0657]: `impl Trait` can only capture lifetimes bound at the fn or impl level
--> $DIR/E0657.rs:10:31
|
LL | -> Box<for<'a> Id<impl Lt<'a>>>
| ^^

error[E0657]: `impl Trait` can only capture lifetimes bound at the fn or impl level
--> $DIR/E0657.rs:19:35
--> $DIR/E0657.rs:20:35
|
LL | -> Box<for<'a> Id<impl Lt<'a>>>
| ^^

error: aborting due to 2 previous errors
error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0657`.
3 changes: 1 addition & 2 deletions src/test/ui/impl-trait/issues/issue-54895.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,3 @@
// check-pass

trait Trait<'a> {
type Out;
fn call(&'a self) -> Self::Out;
Expand All @@ -15,6 +13,7 @@ impl<'a> Trait<'a> for X {
}

fn f() -> impl for<'a> Trait<'a, Out = impl Sized + 'a> {
//~^ ERROR lifetime bounds on nested opaque types are not supported yet
X(())
}

Expand Down
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