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Rollup merge of #100247 - cjgillot:verify-dyn-trait-alias-defaults, r…
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…=lcnr

Generalize trait object generic param check to aliases.

The current algorithm only checks that `Self` does not appear in defaults for traits.  This is not sufficient for trait aliases.
This PR moves the check to trait object elaboration, which sees through trait aliases.

Fixes #82927.
Fixes #84789.
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@Dylan-DPC
Dylan-DPC authored Aug 12, 2022
2 parents 392ba5f + 0df84ae commit caac670
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Showing 11 changed files with 178 additions and 132 deletions.
156 changes: 77 additions & 79 deletions compiler/rustc_typeck/src/astconv/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ use rustc_trait_selection::traits::error_reporting::{
};
use rustc_trait_selection::traits::wf::object_region_bounds;

use smallvec::SmallVec;
use smallvec::{smallvec, SmallVec};
use std::collections::BTreeSet;
use std::slice;

Expand Down Expand Up @@ -368,36 +368,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
return (tcx.intern_substs(&[]), arg_count);
}

let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);

struct SubstsForAstPathCtxt<'a, 'tcx> {
astconv: &'a (dyn AstConv<'tcx> + 'a),
def_id: DefId,
generic_args: &'a GenericArgs<'a>,
span: Span,
missing_type_params: Vec<Symbol>,
inferred_params: Vec<Span>,
infer_args: bool,
is_object: bool,
}

impl<'tcx, 'a> SubstsForAstPathCtxt<'tcx, 'a> {
fn default_needs_object_self(&mut self, param: &ty::GenericParamDef) -> bool {
let tcx = self.astconv.tcx();
if let GenericParamDefKind::Type { has_default, .. } = param.kind {
if self.is_object && has_default {
let default_ty = tcx.at(self.span).type_of(param.def_id);
let self_param = tcx.types.self_param;
if default_ty.walk().any(|arg| arg == self_param.into()) {
// There is no suitable inference default for a type parameter
// that references self, in an object type.
return true;
}
}
}

false
}
}

impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for SubstsForAstPathCtxt<'a, 'tcx> {
Expand Down Expand Up @@ -500,41 +477,23 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
GenericParamDefKind::Type { has_default, .. } => {
if !infer_args && has_default {
// No type parameter provided, but a default exists.

// If we are converting an object type, then the
// `Self` parameter is unknown. However, some of the
// other type parameters may reference `Self` in their
// defaults. This will lead to an ICE if we are not
// careful!
if self.default_needs_object_self(param) {
self.missing_type_params.push(param.name);
tcx.ty_error().into()
} else {
// This is a default type parameter.
let substs = substs.unwrap();
if substs.iter().any(|arg| match arg.unpack() {
GenericArgKind::Type(ty) => ty.references_error(),
_ => false,
}) {
// Avoid ICE #86756 when type error recovery goes awry.
return tcx.ty_error().into();
}
self.astconv
.normalize_ty(
self.span,
EarlyBinder(tcx.at(self.span).type_of(param.def_id))
.subst(tcx, substs),
)
.into()
let substs = substs.unwrap();
if substs.iter().any(|arg| match arg.unpack() {
GenericArgKind::Type(ty) => ty.references_error(),
_ => false,
}) {
// Avoid ICE #86756 when type error recovery goes awry.
return tcx.ty_error().into();
}
self.astconv
.normalize_ty(
self.span,
EarlyBinder(tcx.at(self.span).type_of(param.def_id))
.subst(tcx, substs),
)
.into()
} else if infer_args {
// No type parameters were provided, we can infer all.
let param = if !self.default_needs_object_self(param) {
Some(param)
} else {
None
};
self.astconv.ty_infer(param, self.span).into()
self.astconv.ty_infer(Some(param), self.span).into()
} else {
// We've already errored above about the mismatch.
tcx.ty_error().into()
Expand Down Expand Up @@ -564,10 +523,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
def_id,
span,
generic_args,
missing_type_params: vec![],
inferred_params: vec![],
infer_args,
is_object,
};
let substs = Self::create_substs_for_generic_args(
tcx,
Expand All @@ -579,13 +536,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
&mut substs_ctx,
);

self.complain_about_missing_type_params(
substs_ctx.missing_type_params,
def_id,
span,
generic_args.args.is_empty(),
);

debug!(
"create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
generics, self_ty, substs
Expand Down Expand Up @@ -1490,23 +1440,71 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
// Erase the `dummy_self` (`trait_object_dummy_self`) used above.
let existential_trait_refs = regular_traits.iter().map(|i| {
i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
if trait_ref.self_ty() != dummy_self {
// FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
// which picks up non-supertraits where clauses - but also, the object safety
// completely ignores trait aliases, which could be object safety hazards. We
// `delay_span_bug` here to avoid an ICE in stable even when the feature is
// disabled. (#66420)
tcx.sess.delay_span_bug(
DUMMY_SP,
&format!(
"trait_ref_to_existential called on {:?} with non-dummy Self",
trait_ref,
),
assert_eq!(trait_ref.self_ty(), dummy_self);

// Verify that `dummy_self` did not leak inside default type parameters. This
// could not be done at path creation, since we need to see through trait aliases.
let mut missing_type_params = vec![];
let mut references_self = false;
let generics = tcx.generics_of(trait_ref.def_id);
let substs: Vec<_> = trait_ref
.substs
.iter()
.enumerate()
.skip(1) // Remove `Self` for `ExistentialPredicate`.
.map(|(index, arg)| {
if let ty::GenericArgKind::Type(ty) = arg.unpack() {
debug!(?ty);
if ty == dummy_self {
let param = &generics.params[index];
missing_type_params.push(param.name);
tcx.ty_error().into()
} else if ty.walk().any(|arg| arg == dummy_self.into()) {
references_self = true;
tcx.ty_error().into()
} else {
arg
}
} else {
arg
}
})
.collect();
let substs = tcx.intern_substs(&substs[..]);

let span = i.bottom().1;
let empty_generic_args = trait_bounds.iter().any(|hir_bound| {
hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
&& hir_bound.span.contains(span)
});
self.complain_about_missing_type_params(
missing_type_params,
trait_ref.def_id,
span,
empty_generic_args,
);

if references_self {
let def_id = i.bottom().0.def_id();
let mut err = struct_span_err!(
tcx.sess,
i.bottom().1,
E0038,
"the {} `{}` cannot be made into an object",
tcx.def_kind(def_id).descr(def_id),
tcx.item_name(def_id),
);
err.note(
rustc_middle::traits::ObjectSafetyViolation::SupertraitSelf(smallvec![])
.error_msg(),
);
err.emit();
}
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)

ty::ExistentialTraitRef { def_id: trait_ref.def_id, substs }
})
});

let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
bound.map_bound(|b| {
if b.projection_ty.self_ty() != dummy_self {
Expand Down
46 changes: 23 additions & 23 deletions src/test/ui/associated-types/issue-22560.stderr
View file
Original file line number Diff line number Diff line change
@@ -1,25 +1,3 @@
error[E0393]: the type parameter `Rhs` must be explicitly specified
--> $DIR/issue-22560.rs:9:23
|
LL | trait Sub<Rhs=Self> {
| ------------------- type parameter `Rhs` must be specified for this
...
LL | type Test = dyn Add + Sub;
| ^^^ help: set the type parameter to the desired type: `Sub<Rhs>`
|
= note: because of the default `Self` reference, type parameters must be specified on object types

error[E0393]: the type parameter `Rhs` must be explicitly specified
--> $DIR/issue-22560.rs:9:17
|
LL | trait Add<Rhs=Self> {
| ------------------- type parameter `Rhs` must be specified for this
...
LL | type Test = dyn Add + Sub;
| ^^^ help: set the type parameter to the desired type: `Add<Rhs>`
|
= note: because of the default `Self` reference, type parameters must be specified on object types

error[E0225]: only auto traits can be used as additional traits in a trait object
--> $DIR/issue-22560.rs:9:23
|
Expand All @@ -28,7 +6,7 @@ LL | type Test = dyn Add + Sub;
| |
| first non-auto trait
|
= help: consider creating a new trait with all of these as supertraits and using that trait here instead: `trait NewTrait: Add<[type error]> + Sub<[type error]> {}`
= help: consider creating a new trait with all of these as supertraits and using that trait here instead: `trait NewTrait: Add + Sub {}`
= note: auto-traits like `Send` and `Sync` are traits that have special properties; for more information on them, visit <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>

error[E0191]: the value of the associated types `Output` (from trait `Add`), `Output` (from trait `Sub`) must be specified
Expand All @@ -50,6 +28,28 @@ help: specify the associated types
LL | type Test = dyn Add<Output = Type> + Sub<Output = Type>;
| ~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~

error[E0393]: the type parameter `Rhs` must be explicitly specified
--> $DIR/issue-22560.rs:9:17
|
LL | trait Add<Rhs=Self> {
| ------------------- type parameter `Rhs` must be specified for this
...
LL | type Test = dyn Add + Sub;
| ^^^ help: set the type parameter to the desired type: `Add<Rhs>`
|
= note: because of the default `Self` reference, type parameters must be specified on object types

error[E0393]: the type parameter `Rhs` must be explicitly specified
--> $DIR/issue-22560.rs:9:23
|
LL | trait Sub<Rhs=Self> {
| ------------------- type parameter `Rhs` must be specified for this
...
LL | type Test = dyn Add + Sub;
| ^^^ help: set the type parameter to the desired type: `Sub<Rhs>`
|
= note: because of the default `Self` reference, type parameters must be specified on object types

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0191, E0225, E0393.
Expand Down
1 change: 0 additions & 1 deletion src/test/ui/cycle-trait/cycle-trait-default-type-trait.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@

trait Foo<X = Box<dyn Foo>> {
//~^ ERROR cycle detected
//~| ERROR cycle detected
}

fn main() { }
21 changes: 1 addition & 20 deletions src/test/ui/cycle-trait/cycle-trait-default-type-trait.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,30 +10,11 @@ note: cycle used when collecting item types in top-level module
|
LL | / trait Foo<X = Box<dyn Foo>> {
LL | |
LL | |
LL | | }
LL | |
LL | | fn main() { }
| |_____________^

error[E0391]: cycle detected when computing type of `Foo::X`
--> $DIR/cycle-trait-default-type-trait.rs:4:23
|
LL | trait Foo<X = Box<dyn Foo>> {
| ^^^
|
= note: ...which immediately requires computing type of `Foo::X` again
note: cycle used when collecting item types in top-level module
--> $DIR/cycle-trait-default-type-trait.rs:4:1
|
LL | / trait Foo<X = Box<dyn Foo>> {
LL | |
LL | |
LL | | }
LL | |
LL | | fn main() { }
| |_____________^

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

For more information about this error, try `rustc --explain E0391`.
18 changes: 9 additions & 9 deletions src/test/ui/issues/issue-21950.stderr
View file
Original file line number Diff line number Diff line change
@@ -1,3 +1,12 @@
error[E0191]: the value of the associated type `Output` (from trait `Add`) must be specified
--> $DIR/issue-21950.rs:10:25
|
LL | type Output;
| ----------- `Output` defined here
...
LL | let x = &10 as &dyn Add;
| ^^^ help: specify the associated type: `Add<Output = Type>`

error[E0393]: the type parameter `Rhs` must be explicitly specified
--> $DIR/issue-21950.rs:10:25
|
Expand All @@ -9,15 +18,6 @@ LL | let x = &10 as &dyn Add;
|
= note: because of the default `Self` reference, type parameters must be specified on object types

error[E0191]: the value of the associated type `Output` (from trait `Add`) must be specified
--> $DIR/issue-21950.rs:10:25
|
LL | type Output;
| ----------- `Output` defined here
...
LL | let x = &10 as &dyn Add;
| ^^^ help: specify the associated type: `Add<Output = Type>`

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0191, E0393.
Expand Down
10 changes: 10 additions & 0 deletions src/test/ui/traits/alias/generic-default-in-dyn.rs
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
trait SendEqAlias<T> = PartialEq;
//~^ ERROR trait aliases are experimental

struct Foo<T>(dyn SendEqAlias<T>);
//~^ ERROR the type parameter `Rhs` must be explicitly specified [E0393]

struct Bar<T>(dyn SendEqAlias<T>, T);
//~^ ERROR the type parameter `Rhs` must be explicitly specified [E0393]

fn main() {}
39 changes: 39 additions & 0 deletions src/test/ui/traits/alias/generic-default-in-dyn.stderr
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,39 @@
error[E0658]: trait aliases are experimental
--> $DIR/generic-default-in-dyn.rs:1:1
|
LL | trait SendEqAlias<T> = PartialEq;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #41517 <https://github.com/rust-lang/rust/issues/41517> for more information
= help: add `#![feature(trait_alias)]` to the crate attributes to enable

error[E0393]: the type parameter `Rhs` must be explicitly specified
--> $DIR/generic-default-in-dyn.rs:4:19
|
LL | struct Foo<T>(dyn SendEqAlias<T>);
| ^^^^^^^^^^^^^^ missing reference to `Rhs`
|
::: $SRC_DIR/core/src/cmp.rs:LL:COL
|
LL | pub trait PartialEq<Rhs: ?Sized = Self> {
| --------------------------------------- type parameter `Rhs` must be specified for this
|
= note: because of the default `Self` reference, type parameters must be specified on object types

error[E0393]: the type parameter `Rhs` must be explicitly specified
--> $DIR/generic-default-in-dyn.rs:7:19
|
LL | struct Bar<T>(dyn SendEqAlias<T>, T);
| ^^^^^^^^^^^^^^ missing reference to `Rhs`
|
::: $SRC_DIR/core/src/cmp.rs:LL:COL
|
LL | pub trait PartialEq<Rhs: ?Sized = Self> {
| --------------------------------------- type parameter `Rhs` must be specified for this
|
= note: because of the default `Self` reference, type parameters must be specified on object types

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0393, E0658.
For more information about an error, try `rustc --explain E0393`.
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