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Simplify collection of in-band lifetimes #91640

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Dec 11, 2021
Merged

Simplify collection of in-band lifetimes #91640

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6e7ec0c
Simplify collect_in_band_defs.
cjgillot Nov 12, 2021
72b6f70
Use collect_in_band_defs for async lifetime captures.
cjgillot Nov 29, 2021
8576ab4
Store impl_trait_fn inside OpaqueTyOrigin.
cjgillot Nov 30, 2021
54ff721
Simplify match.
cjgillot Dec 7, 2021
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9 changes: 2 additions & 7 deletions compiler/rustc_ast_lowering/src/item.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -247,12 +247,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
AnonymousLifetimeMode::PassThrough,
|this, idty| {
let ret_id = asyncness.opt_return_id();
this.lower_fn_decl(
&decl,
Some((fn_def_id.to_def_id(), idty)),
true,
ret_id,
)
this.lower_fn_decl(&decl, Some((fn_def_id, idty)), true, ret_id)
},
);
let sig = hir::FnSig {
Expand Down Expand Up @@ -1264,7 +1259,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
|this, idty| {
this.lower_fn_decl(
&sig.decl,
Some((fn_def_id.to_def_id(), idty)),
Some((fn_def_id, idty)),
impl_trait_return_allow,
is_async,
)
Expand Down
192 changes: 87 additions & 105 deletions compiler/rustc_ast_lowering/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -228,7 +228,7 @@ enum ImplTraitContext<'b, 'a> {
ReturnPositionOpaqueTy {
/// `DefId` for the parent function, used to look up necessary
/// information later.
fn_def_id: DefId,
fn_def_id: LocalDefId,
/// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
origin: hir::OpaqueTyOrigin,
},
Expand Down Expand Up @@ -646,31 +646,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
/// parameter while `f` is running (and restored afterwards).
fn collect_in_band_defs<T>(
&mut self,
parent_def_id: LocalDefId,
anonymous_lifetime_mode: AnonymousLifetimeMode,
f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
) -> (Vec<hir::GenericParam<'hir>>, T) {
assert!(!self.is_collecting_in_band_lifetimes);
assert!(self.lifetimes_to_define.is_empty());
let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;

self.anonymous_lifetime_mode = anonymous_lifetime_mode;
self.is_collecting_in_band_lifetimes = true;

let (in_band_ty_params, res) = f(self);

self.is_collecting_in_band_lifetimes = false;
self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;

let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
f: impl FnOnce(&mut Self) -> T,
) -> (Vec<(Span, ParamName)>, T) {
let was_collecting = std::mem::replace(&mut self.is_collecting_in_band_lifetimes, true);
let len = self.lifetimes_to_define.len();

let params = lifetimes_to_define
.into_iter()
.map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
.chain(in_band_ty_params.into_iter())
.collect();
let res = f(self);

(params, res)
let lifetimes_to_define = self.lifetimes_to_define.split_off(len);
self.is_collecting_in_band_lifetimes = was_collecting;
(lifetimes_to_define, res)
}

/// Converts a lifetime into a new generic parameter.
Expand Down Expand Up @@ -785,27 +770,39 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
anonymous_lifetime_mode: AnonymousLifetimeMode,
f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
) -> (hir::Generics<'hir>, T) {
let (in_band_defs, (mut lowered_generics, res)) =
self.with_in_scope_lifetime_defs(&generics.params, |this| {
this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
let mut params = Vec::new();
// Note: it is necessary to lower generics *before* calling `f`.
// When lowering `async fn`, there's a final step when lowering
// the return type that assumes that all in-scope lifetimes have
// already been added to either `in_scope_lifetimes` or
// `lifetimes_to_define`. If we swapped the order of these two,
// in-band-lifetimes introduced by generics or where-clauses
// wouldn't have been added yet.
let generics = this.lower_generics_mut(
generics,
ImplTraitContext::Universal(&mut params, this.current_hir_id_owner),
);
let res = f(this, &mut params);
(params, (generics, res))
let (lifetimes_to_define, (mut lowered_generics, impl_trait_defs, res)) = self
.collect_in_band_defs(|this| {
this.with_anonymous_lifetime_mode(anonymous_lifetime_mode, |this| {
this.with_in_scope_lifetime_defs(&generics.params, |this| {
let mut impl_trait_defs = Vec::new();
// Note: it is necessary to lower generics *before* calling `f`.
// When lowering `async fn`, there's a final step when lowering
// the return type that assumes that all in-scope lifetimes have
// already been added to either `in_scope_lifetimes` or
// `lifetimes_to_define`. If we swapped the order of these two,
// in-band-lifetimes introduced by generics or where-clauses
// wouldn't have been added yet.
let generics = this.lower_generics_mut(
generics,
ImplTraitContext::Universal(
&mut impl_trait_defs,
this.current_hir_id_owner,
),
);
let res = f(this, &mut impl_trait_defs);
(generics, impl_trait_defs, res)
})
})
});

lowered_generics.params.extend(in_band_defs);
lowered_generics.params.extend(
lifetimes_to_define
.into_iter()
.map(|(span, hir_name)| {
self.lifetime_to_generic_param(span, hir_name, parent_def_id)
})
.chain(impl_trait_defs),
);

let lowered_generics = lowered_generics.into_generics(self.arena);
(lowered_generics, res)
Expand Down Expand Up @@ -1380,7 +1377,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
fn lower_opaque_impl_trait(
&mut self,
span: Span,
fn_def_id: Option<DefId>,
fn_def_id: Option<LocalDefId>,
origin: hir::OpaqueTyOrigin,
opaque_ty_node_id: NodeId,
capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
Expand Down Expand Up @@ -1452,7 +1449,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
span: lctx.lower_span(span),
},
bounds: hir_bounds,
impl_trait_fn: fn_def_id,
origin,
};

Expand Down Expand Up @@ -1522,7 +1518,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
fn lower_fn_decl(
&mut self,
decl: &FnDecl,
mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
mut in_band_ty_params: Option<(LocalDefId, &mut Vec<hir::GenericParam<'hir>>)>,
impl_trait_return_allow: bool,
make_ret_async: Option<NodeId>,
) -> &'hir hir::FnDecl<'hir> {
Expand Down Expand Up @@ -1580,7 +1576,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
Some((def_id, _)) if impl_trait_return_allow => {
ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id: def_id,
origin: hir::OpaqueTyOrigin::FnReturn,
origin: hir::OpaqueTyOrigin::FnReturn(def_id),
}
}
_ => ImplTraitContext::disallowed(),
Expand Down Expand Up @@ -1635,7 +1631,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
fn lower_async_fn_ret_ty(
&mut self,
output: &FnRetTy,
fn_def_id: DefId,
fn_def_id: LocalDefId,
opaque_ty_node_id: NodeId,
) -> hir::FnRetTy<'hir> {
debug!(
Expand Down Expand Up @@ -1689,18 +1685,29 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// this is because the elided lifetimes from the return type
// should be figured out using the ordinary elision rules, and
// this desugaring achieves that.

debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", self.in_scope_lifetimes);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", self.lifetimes_to_define);

// Calculate all the lifetimes that should be captured
// by the opaque type. This should include all in-scope
// lifetime parameters, including those defined in-band.
//
// The variable `input_lifetimes_count` tracks the number of
// lifetime parameters to the opaque type *not counting* those
// lifetimes elided in the return type. This includes those
// that are explicitly declared (`in_scope_lifetimes`) and
// those elided lifetimes we found in the arguments (current
// content of `lifetimes_to_define`). Next, we will process
// the return type, which will cause `lifetimes_to_define` to
// grow.
let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();

let mut lifetime_params = Vec::new();
// `lifetime_params` is a vector of tuple (span, parameter name, lifetime name).

// Input lifetime like `'a` or `'1`:
let mut lifetime_params: Vec<_> = self
.in_scope_lifetimes
.iter()
.cloned()
.map(|name| (name.ident().span, name, hir::LifetimeName::Param(name)))
.chain(
self.lifetimes_to_define
.iter()
.map(|&(span, name)| (span, name, hir::LifetimeName::Param(name))),
)
.collect();

self.with_hir_id_owner(opaque_ty_node_id, |this| {
// We have to be careful to get elision right here. The
// idea is that we create a lifetime parameter for each
Expand All @@ -1710,34 +1717,26 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
//
// Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
// hence the elision takes place at the fn site.
let future_bound = this
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
let (lifetimes_to_define, future_bound) =
this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
this.collect_in_band_defs(|this| {
this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
})
});

debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", lifetimes_to_define);

// Calculate all the lifetimes that should be captured
// by the opaque type. This should include all in-scope
// lifetime parameters, including those defined in-band.
//
// Note: this must be done after lowering the output type,
// as the output type may introduce new in-band lifetimes.
lifetime_params = this
.in_scope_lifetimes
.iter()
.cloned()
.map(|name| (name.ident().span, name))
.chain(this.lifetimes_to_define.iter().cloned())
.collect();

debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
lifetime_params.extend(
// Output lifetime like `'_`:
lifetimes_to_define
.into_iter()
.map(|(span, name)| (span, name, hir::LifetimeName::Implicit(false))),
);
debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);

let generic_params =
this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
this.arena.alloc_from_iter(lifetime_params.iter().map(|&(span, hir_name, _)| {
this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_id)
}));

let opaque_ty_item = hir::OpaqueTy {
Expand All @@ -1747,8 +1746,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
span: this.lower_span(span),
},
bounds: arena_vec![this; future_bound],
impl_trait_fn: Some(fn_def_id),
origin: hir::OpaqueTyOrigin::AsyncFn,
origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
};

trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
Expand All @@ -1771,25 +1769,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
//
// For the "output" lifetime parameters, we just want to
// generate `'_`.
let mut generic_args = Vec::with_capacity(lifetime_params.len());
generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map(
|&(span, hir_name)| {
// Input lifetime like `'a` or `'1`:
let generic_args =
self.arena.alloc_from_iter(lifetime_params.into_iter().map(|(span, _, name)| {
GenericArg::Lifetime(hir::Lifetime {
hir_id: self.next_id(),
span: self.lower_span(span),
name: hir::LifetimeName::Param(hir_name),
name,
})
},
));
generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
// Output lifetime like `'_`.
GenericArg::Lifetime(hir::Lifetime {
hir_id: self.next_id(),
span: self.lower_span(span),
name: hir::LifetimeName::Implicit(false),
})));
let generic_args = self.arena.alloc_from_iter(generic_args);
}));

// Create the `Foo<...>` reference itself. Note that the `type
// Foo = impl Trait` is, internally, created as a child of the
Expand All @@ -1805,7 +1792,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
fn lower_async_fn_output_type_to_future_bound(
&mut self,
output: &FnRetTy,
fn_def_id: DefId,
fn_def_id: LocalDefId,
span: Span,
) -> hir::GenericBound<'hir> {
// Compute the `T` in `Future<Output = T>` from the return type.
Expand All @@ -1816,7 +1803,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// generates.
let context = ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id,
origin: hir::OpaqueTyOrigin::FnReturn,
origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
};
self.lower_ty(ty, context)
}
Expand Down Expand Up @@ -2453,17 +2440,12 @@ impl<'hir> GenericArgsCtor<'hir> {
}
}

#[tracing::instrument(level = "debug")]
fn lifetimes_from_impl_trait_bounds(
opaque_ty_id: NodeId,
bounds: hir::GenericBounds<'_>,
lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
) -> Vec<(hir::LifetimeName, Span)> {
debug!(
"lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
bounds={:#?})",
opaque_ty_id, bounds,
);

// This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
// appear in the bounds, excluding lifetimes that are created within the bounds.
// E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_borrowck/src/region_infer/opaque_types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -173,7 +173,7 @@ fn check_opaque_type_parameter_valid(
// fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
//
// which would error here on all of the `'static` args.
OpaqueTyOrigin::FnReturn | OpaqueTyOrigin::AsyncFn => return true,
OpaqueTyOrigin::FnReturn(..) | OpaqueTyOrigin::AsyncFn(..) => return true,
// Check these
OpaqueTyOrigin::TyAlias => {}
}
Expand Down
9 changes: 5 additions & 4 deletions compiler/rustc_hir/src/hir.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2248,17 +2248,16 @@ pub struct BareFnTy<'hir> {
pub struct OpaqueTy<'hir> {
pub generics: Generics<'hir>,
pub bounds: GenericBounds<'hir>,
pub impl_trait_fn: Option<DefId>,
pub origin: OpaqueTyOrigin,
}

/// From whence the opaque type came.
#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
pub enum OpaqueTyOrigin {
/// `-> impl Trait`
FnReturn,
FnReturn(LocalDefId),
/// `async fn`
AsyncFn,
AsyncFn(LocalDefId),
/// type aliases: `type Foo = impl Trait;`
TyAlias,
}
Expand Down Expand Up @@ -2809,7 +2808,9 @@ impl ItemKind<'_> {
Some(match *self {
ItemKind::Fn(_, ref generics, _)
| ItemKind::TyAlias(_, ref generics)
| ItemKind::OpaqueTy(OpaqueTy { ref generics, impl_trait_fn: None, .. })
| ItemKind::OpaqueTy(OpaqueTy {
ref generics, origin: OpaqueTyOrigin::TyAlias, ..
})
| ItemKind::Enum(_, ref generics)
| ItemKind::Struct(_, ref generics)
| ItemKind::Union(_, ref generics)
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
kind:
hir::ItemKind::OpaqueTy(hir::OpaqueTy {
bounds,
origin: hir::OpaqueTyOrigin::AsyncFn,
origin: hir::OpaqueTyOrigin::AsyncFn(..),
..
}),
..
Expand Down
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