diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs index dbf55db6e6b..7fbf4fbf085 100644 --- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs +++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs @@ -1,10 +1,10 @@ -use rustc_data_structures::fx::{FxIndexMap, FxIndexSet}; +use rustc_data_structures::fx::FxIndexMap; use rustc_errors::ErrorGuaranteed; use rustc_hir::def::DefKind; use rustc_hir::def_id::LocalDefId; use rustc_hir::OpaqueTyOrigin; -use rustc_infer::infer::InferCtxt; use rustc_infer::infer::TyCtxtInferExt as _; +use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin}; use rustc_infer::traits::{Obligation, ObligationCause}; use rustc_macros::extension; use rustc_middle::traits::DefiningAnchor; @@ -95,8 +95,8 @@ impl<'tcx> RegionInferenceContext<'tcx> { /// For example consider `fn f<'a>(x: &'a i32) -> impl Sized + 'a { x }`. /// This is lowered to give HIR something like /// - /// type f<'a>::_Return<'_a> = impl Sized + '_a; - /// fn f<'a>(x: &'a i32) -> f<'static>::_Return<'a> { x } + /// type f<'a>::_Return<'_x> = impl Sized + '_x; + /// fn f<'a>(x: &'a i32) -> f<'a>::_Return<'a> { x } /// /// When checking the return type record the type from the return and the /// type used in the return value. In this case they might be `_Return<'1>` @@ -104,30 +104,34 @@ impl<'tcx> RegionInferenceContext<'tcx> { /// /// Once we to this method, we have completed region inference and want to /// call `infer_opaque_definition_from_instantiation` to get the inferred - /// type of `_Return<'_a>`. `infer_opaque_definition_from_instantiation` + /// type of `_Return<'_x>`. `infer_opaque_definition_from_instantiation` /// compares lifetimes directly, so we need to map the inference variables /// back to concrete lifetimes: `'static`, `ReEarlyParam` or `ReLateParam`. /// - /// First we map all the lifetimes in the concrete type to an equal - /// universal region that occurs in the concrete type's args, in this case - /// this would result in `&'1 i32`. We only consider regions in the args + /// First we map the regions in the the generic parameters `_Return<'1>` to + /// their `external_name` giving `_Return<'a>`. This step is a bit involved. + /// See the [rustc-dev-guide chapter] for more info. + /// + /// Then we map all the lifetimes in the concrete type to an equal + /// universal region that occurs in the opaque type's args, in this case + /// this would result in `&'a i32`. We only consider regions in the args /// in case there is an equal region that does not. For example, this should /// be allowed: /// `fn f<'a: 'b, 'b: 'a>(x: *mut &'b i32) -> impl Sized + 'a { x }` /// - /// Then we map the regions in both the type and the generic parameters to their - /// `external_name` giving `concrete_type = &'a i32`, - /// `args = ['static, 'a]`. This will then allow - /// `infer_opaque_definition_from_instantiation` to determine that - /// `_Return<'_a> = &'_a i32`. + /// This will then allow `infer_opaque_definition_from_instantiation` to + /// determine that `_Return<'_x> = &'_x i32`. /// /// There's a slight complication around closures. Given /// `fn f<'a: 'a>() { || {} }` the closure's type is something like /// `f::<'a>::{{closure}}`. The region parameter from f is essentially /// ignored by type checking so ends up being inferred to an empty region. /// Calling `universal_upper_bound` for such a region gives `fr_fn_body`, - /// which has no `external_name` in which case we use `'empty` as the + /// which has no `external_name` in which case we use `'{erased}` as the /// region to pass to `infer_opaque_definition_from_instantiation`. + /// + /// [rustc-dev-guide chapter]: + /// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html #[instrument(level = "debug", skip(self, infcx), ret)] pub(crate) fn infer_opaque_types( &self, @@ -138,85 +142,59 @@ impl<'tcx> RegionInferenceContext<'tcx> { let mut result: FxIndexMap> = FxIndexMap::default(); - let member_constraints: FxIndexMap<_, _> = self - .member_constraints - .all_indices() - .map(|ci| (self.member_constraints[ci].key, ci)) - .collect(); - debug!(?member_constraints); - for (opaque_type_key, concrete_type) in opaque_ty_decls { - let args = opaque_type_key.args; - debug!(?concrete_type, ?args); + debug!(?opaque_type_key, ?concrete_type); - let mut arg_regions = vec![self.universal_regions.fr_static]; - - let to_universal_region = |vid, arg_regions: &mut Vec<_>| match self.universal_name(vid) - { - Some(region) => { - let vid = self.universal_regions.to_region_vid(region); - arg_regions.push(vid); - region - } - None => { - arg_regions.push(vid); - ty::Region::new_error_with_message( - infcx.tcx, - concrete_type.span, - "opaque type with non-universal region args", - ) - } - }; - - // Start by inserting universal regions from the member_constraint choice regions. - // This will ensure they get precedence when folding the regions in the concrete type. - if let Some(&ci) = member_constraints.get(&opaque_type_key) { - for &vid in self.member_constraints.choice_regions(ci) { - to_universal_region(vid, &mut arg_regions); - } - } - debug!(?arg_regions); - - // Next, insert universal regions from args, so we can translate regions that appear - // in them but are not subject to member constraints, for instance closure args. - let universal_key = opaque_type_key.fold_captured_lifetime_args(infcx.tcx, |region| { - if let ty::RePlaceholder(..) = region.kind() { - // Higher kinded regions don't need remapping, they don't refer to anything outside of this the args. - return region; - } - let vid = self.to_region_vid(region); - to_universal_region(vid, &mut arg_regions) - }); - let universal_args = universal_key.args; - debug!(?universal_args); - debug!(?arg_regions); - - // Deduplicate the set of regions while keeping the chosen order. - let arg_regions = arg_regions.into_iter().collect::>(); - debug!(?arg_regions); - - let universal_concrete_type = - infcx.tcx.fold_regions(concrete_type, |region, _| match *region { - ty::ReVar(vid) => arg_regions - .iter() - .find(|ur_vid| self.eval_equal(vid, **ur_vid)) - .and_then(|ur_vid| self.definitions[*ur_vid].external_name) - .unwrap_or(infcx.tcx.lifetimes.re_erased), - ty::RePlaceholder(_) => ty::Region::new_error_with_message( - infcx.tcx, - concrete_type.span, - "hidden type contains placeholders, we don't support higher kinded opaques yet", - ), - _ => region, - }); - debug!(?universal_concrete_type); + let mut arg_regions: Vec<(ty::RegionVid, ty::Region<'_>)> = + vec![(self.universal_regions.fr_static, infcx.tcx.lifetimes.re_static)]; let opaque_type_key = - OpaqueTypeKey { def_id: opaque_type_key.def_id, args: universal_args }; - let ty = infcx.infer_opaque_definition_from_instantiation( - opaque_type_key, - universal_concrete_type, - ); + opaque_type_key.fold_captured_lifetime_args(infcx.tcx, |region| { + // Use the SCC representative instead of directly using `region`. + // See [rustc-dev-guide chapter] § "Strict lifetime equality". + let scc = self.constraint_sccs.scc(region.as_var()); + let vid = self.scc_representatives[scc]; + let named = match self.definitions[vid].origin { + // Iterate over all universal regions in a consistent order and find the + // *first* equal region. This makes sure that equal lifetimes will have + // the same name and simplifies subsequent handling. + // See [rustc-dev-guide chapter] § "Semantic lifetime equality". + NllRegionVariableOrigin::FreeRegion => self + .universal_regions + .universal_regions() + .filter(|&ur| self.universal_region_relations.equal(vid, ur)) + // FIXME(aliemjay): universal regions with no `external_name` + // are extenal closure regions, which should be rejected eventually. + .find_map(|ur| self.definitions[ur].external_name), + NllRegionVariableOrigin::Placeholder(placeholder) => { + Some(ty::Region::new_placeholder(infcx.tcx, placeholder)) + } + NllRegionVariableOrigin::Existential { .. } => None, + } + .unwrap_or_else(|| { + ty::Region::new_error_with_message( + infcx.tcx, + concrete_type.span, + "opaque type with non-universal region args", + ) + }); + + arg_regions.push((vid, named)); + named + }); + debug!(?opaque_type_key, ?arg_regions); + + let concrete_type = infcx.tcx.fold_regions(concrete_type, |region, _| { + arg_regions + .iter() + .find(|&&(arg_vid, _)| self.eval_equal(region.as_var(), arg_vid)) + .map(|&(_, arg_named)| arg_named) + .unwrap_or(infcx.tcx.lifetimes.re_erased) + }); + debug!(?concrete_type); + + let ty = + infcx.infer_opaque_definition_from_instantiation(opaque_type_key, concrete_type); // Sometimes two opaque types are the same only after we remap the generic parameters // back to the opaque type definition. E.g. we may have `OpaqueType` mapped to `(X, Y)` // and `OpaqueType` mapped to `(Y, X)`, and those are the same, but we only know that diff --git a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs index 86d20599a2a..7553e3ee04f 100644 --- a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs +++ b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs @@ -164,6 +164,13 @@ impl UniversalRegionRelations<'_> { self.outlives.contains(fr1, fr2) } + /// Returns `true` if fr1 is known to equal fr2. + /// + /// This will only ever be true for universally quantified regions. + pub(crate) fn equal(&self, fr1: RegionVid, fr2: RegionVid) -> bool { + self.outlives.contains(fr1, fr2) && self.outlives.contains(fr2, fr1) + } + /// Returns a vector of free regions `x` such that `fr1: x` is /// known to hold. pub(crate) fn regions_outlived_by(&self, fr1: RegionVid) -> Vec { diff --git a/tests/ui/type-alias-impl-trait/defined-by-user-annotation.rs b/tests/ui/type-alias-impl-trait/defined-by-user-annotation.rs index d97a3010a17..0e1d44e7bb3 100644 --- a/tests/ui/type-alias-impl-trait/defined-by-user-annotation.rs +++ b/tests/ui/type-alias-impl-trait/defined-by-user-annotation.rs @@ -8,12 +8,24 @@ impl Equate for T { type Proj = T; } trait Indirect { type Ty; } impl> Indirect for (A, B) { type Ty = (); } -type Opq = impl Sized; -fn define_1(_: Opq) { - let _ = None::<<(Opq, u8) as Indirect>::Ty>; +mod basic { + use super::*; + type Opq = impl Sized; + fn define_1(_: Opq) { + let _ = None::<<(Opq, u8) as Indirect>::Ty>; + } + fn define_2() -> Opq { + 0u8 + } } -fn define_2() -> Opq { - 0u8 + +// `Opq<'a> == &'b u8` shouldn't be an error because `'a == 'b`. +mod lifetime { + use super::*; + type Opq<'a> = impl Sized + 'a; + fn define<'a: 'b, 'b: 'a>(_: Opq<'a>) { + let _ = None::<<(Opq<'a>, &'b u8) as Indirect>::Ty>; + } } fn main() {} diff --git a/tests/ui/type-alias-impl-trait/equal-lifetime-params-not-ok.rs b/tests/ui/type-alias-impl-trait/equal-lifetime-params-not-ok.rs new file mode 100644 index 00000000000..59ba2694a76 --- /dev/null +++ b/tests/ui/type-alias-impl-trait/equal-lifetime-params-not-ok.rs @@ -0,0 +1,37 @@ +// issue: #112841 + +#![feature(type_alias_impl_trait)] + +trait Trait<'a, 'b> {} +impl Trait<'_, '_> for T {} + +mod mod1 { + type Opaque<'a, 'b> = impl super::Trait<'a, 'b>; + fn test<'a>() -> Opaque<'a, 'a> {} + //~^ ERROR non-defining opaque type use in defining scope + //~| ERROR non-defining opaque type use in defining scope +} + +mod mod2 { + type Opaque<'a, 'b> = impl super::Trait<'a, 'b>; + fn test<'a: 'b, 'b: 'a>() -> Opaque<'a, 'b> {} + //~^ ERROR non-defining opaque type use in defining scope +} + +mod mod3 { + type Opaque<'a, 'b> = impl super::Trait<'a, 'b>; + fn test<'a: 'b, 'b: 'a>(a: &'a str) -> Opaque<'a, 'b> { a } + //~^ ERROR non-defining opaque type use in defining scope +} + +// This is similar to the previous cases in that 'a is equal to 'static, +// which is is some sense an implicit parameter to `Opaque`. +// For example, given a defining use `Opaque<'a> := &'a ()`, +// it is ambiguous whether `Opaque<'a> := &'a ()` or `Opaque<'a> := &'static ()` +mod mod4 { + type Opaque<'a> = impl super::Trait<'a, 'a>; + fn test<'a: 'static>() -> Opaque<'a> {} + //~^ ERROR expected generic lifetime parameter, found `'static` +} + +fn main() {} diff --git a/tests/ui/type-alias-impl-trait/equal-lifetime-params-not-ok.stderr b/tests/ui/type-alias-impl-trait/equal-lifetime-params-not-ok.stderr new file mode 100644 index 00000000000..b08bc8b8268 --- /dev/null +++ b/tests/ui/type-alias-impl-trait/equal-lifetime-params-not-ok.stderr @@ -0,0 +1,59 @@ +error: non-defining opaque type use in defining scope + --> $DIR/equal-lifetime-params-not-ok.rs:10:22 + | +LL | fn test<'a>() -> Opaque<'a, 'a> {} + | ^^^^^^^^^^^^^^ generic argument `'a` used twice + | +note: for this opaque type + --> $DIR/equal-lifetime-params-not-ok.rs:9:27 + | +LL | type Opaque<'a, 'b> = impl super::Trait<'a, 'b>; + | ^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: non-defining opaque type use in defining scope + --> $DIR/equal-lifetime-params-not-ok.rs:10:37 + | +LL | fn test<'a>() -> Opaque<'a, 'a> {} + | ^^ + | +note: lifetime used multiple times + --> $DIR/equal-lifetime-params-not-ok.rs:9:17 + | +LL | type Opaque<'a, 'b> = impl super::Trait<'a, 'b>; + | ^^ ^^ + +error: non-defining opaque type use in defining scope + --> $DIR/equal-lifetime-params-not-ok.rs:17:49 + | +LL | fn test<'a: 'b, 'b: 'a>() -> Opaque<'a, 'b> {} + | ^^ + | +note: lifetime used multiple times + --> $DIR/equal-lifetime-params-not-ok.rs:16:17 + | +LL | type Opaque<'a, 'b> = impl super::Trait<'a, 'b>; + | ^^ ^^ + +error: non-defining opaque type use in defining scope + --> $DIR/equal-lifetime-params-not-ok.rs:23:61 + | +LL | fn test<'a: 'b, 'b: 'a>(a: &'a str) -> Opaque<'a, 'b> { a } + | ^ + | +note: lifetime used multiple times + --> $DIR/equal-lifetime-params-not-ok.rs:22:17 + | +LL | type Opaque<'a, 'b> = impl super::Trait<'a, 'b>; + | ^^ ^^ + +error[E0792]: expected generic lifetime parameter, found `'static` + --> $DIR/equal-lifetime-params-not-ok.rs:33:42 + | +LL | type Opaque<'a> = impl super::Trait<'a, 'a>; + | -- cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type +LL | fn test<'a: 'static>() -> Opaque<'a> {} + | ^^ + +error: aborting due to 5 previous errors + +For more information about this error, try `rustc --explain E0792`. diff --git a/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.basic.stderr b/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.basic.stderr new file mode 100644 index 00000000000..e5f86c8c193 --- /dev/null +++ b/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.basic.stderr @@ -0,0 +1,12 @@ +error[E0792]: expected generic lifetime parameter, found `'_` + --> $DIR/generic-not-strictly-equal.rs:33:5 + | +LL | type Opaque<'a> = impl Copy + Captures<'a>; + | -- this generic parameter must be used with a generic lifetime parameter +... +LL | relate(opaque, hidden); // defining use: Opaque<'?1> := u8 + | ^^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to 1 previous error + +For more information about this error, try `rustc --explain E0792`. diff --git a/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.member_constraints.stderr b/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.member_constraints.stderr new file mode 100644 index 00000000000..693af69d6fa --- /dev/null +++ b/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.member_constraints.stderr @@ -0,0 +1,15 @@ +error[E0700]: hidden type for `Opaque<'x>` captures lifetime that does not appear in bounds + --> $DIR/generic-not-strictly-equal.rs:33:5 + | +LL | type Opaque<'a> = impl Copy + Captures<'a>; + | ------------------------ opaque type defined here +LL | +LL | fn test<'x>(_: Opaque<'x>) { + | -- hidden type `&'x u8` captures the lifetime `'x` as defined here +... +LL | relate(opaque, hidden); // defining use: Opaque<'?1> := u8 + | ^^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to 1 previous error + +For more information about this error, try `rustc --explain E0700`. diff --git a/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.rs b/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.rs new file mode 100644 index 00000000000..a059fd3b822 --- /dev/null +++ b/tests/ui/type-alias-impl-trait/generic-not-strictly-equal.rs @@ -0,0 +1,38 @@ +// `Opaque<'?1> := u8` is not a valid defining use here. +// +// Due to fundamental limitations of the member constraints algorithm, +// we require '?1 to be *equal* to some universal region. +// +// While '?1 is eventually inferred to be equal to 'x because of the constraint '?1: 'x, +// we don't consider them equal in the strict sense because they lack the bidirectional outlives +// constraints ['?1: 'x, 'x: '?1]. In NLL terms, they are not part of the same SCC. +// +// See #113971 for details. + +//@ revisions: basic member_constraints +#![feature(type_alias_impl_trait)] + +trait Captures<'a> {} +impl Captures<'_> for T {} + +fn ensure_outlives<'a, X: 'a>(_: X) {} +fn relate(_: X, _: X) {} + +type Opaque<'a> = impl Copy + Captures<'a>; + +fn test<'x>(_: Opaque<'x>) { + let opaque = None::>; // let's call this lifetime '?1 + + #[cfg(basic)] + let hidden = None::; + + #[cfg(member_constraints)] + let hidden = None::<&'x u8>; + + ensure_outlives::<'x>(opaque); // outlives constraint: '?1: 'x + relate(opaque, hidden); // defining use: Opaque<'?1> := u8 + //[basic]~^ ERROR expected generic lifetime parameter, found `'_` + //[member_constraints]~^^ ERROR captures lifetime that does not appear in bounds +} + +fn main() {}