Disallow specializing on const impls with non-const impls.
This commit is contained in:
Ben Reeves
parent
5c25d30f6f
commit
ce03d259da
6 changed files with 52 additions and 81 deletions
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@ -69,6 +69,7 @@ use crate::constrained_generic_params as cgp;
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use crate::errors::SubstsOnOverriddenImpl;
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use rustc_data_structures::fx::FxHashSet;
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use rustc_hir as hir;
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use rustc_hir::def_id::{DefId, LocalDefId};
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use rustc_infer::infer::outlives::env::OutlivesEnvironment;
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use rustc_infer::infer::TyCtxtInferExt;
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@ -117,12 +118,33 @@ fn check_always_applicable(tcx: TyCtxt<'_>, impl1_def_id: LocalDefId, impl2_node
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};
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let span = tcx.def_span(impl1_def_id);
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check_constness(tcx, impl1_def_id, impl2_node, span);
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check_static_lifetimes(tcx, &parent_substs, span);
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check_duplicate_params(tcx, impl1_substs, &parent_substs, span);
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check_predicates(tcx, impl1_def_id, impl1_substs, impl2_node, impl2_substs, span);
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}
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}
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/// Check that the specializing impl `impl1` is at least as const as the base
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/// impl `impl2`
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fn check_constness(tcx: TyCtxt<'_>, impl1_def_id: LocalDefId, impl2_node: Node, span: Span) {
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if impl2_node.is_from_trait() {
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// This isn't a specialization
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return;
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}
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let impl1_constness = tcx.constness(impl1_def_id.to_def_id());
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let impl2_constness = tcx.constness(impl2_node.def_id());
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if let hir::Constness::Const = impl2_constness {
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if let hir::Constness::NotConst = impl1_constness {
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tcx.sess
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.struct_span_err(span, "cannot specialize on const impl with non-const impl")
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.emit();
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}
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}
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}
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/// Given a specializing impl `impl1`, and the base impl `impl2`, returns two
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/// substitutions `(S1, S2)` that equate their trait references. The returned
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/// types are expressed in terms of the generics of `impl1`.
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@ -277,7 +299,7 @@ fn check_static_lifetimes<'tcx>(
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/// Check whether predicates on the specializing impl (`impl1`) are allowed.
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///
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/// Each predicate `P` must be:
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/// Each predicate `P` must be one of:
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///
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/// * Global (not reference any parameters).
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/// * A `T: Tr` predicate where `Tr` is an always-applicable trait.
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@ -375,16 +397,19 @@ fn check_predicates<'tcx>(
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}
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}
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/// Checks whether two predicates are the same for the purposes of specialization.
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/// Checks if some predicate on the specializing impl (`predicate1`) is the same
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/// as some predicate on the base impl (`predicate2`).
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///
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/// This is slightly more complicated than simple syntactic equivalence, since
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/// we want to equate `T: Tr` with `T: ~const Tr` so this can work:
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///
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/// ```ignore (illustrative)
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/// #[rustc_specialization_trait]
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/// trait Specialize { }
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///
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/// impl<T: ~const Bound> const Tr for T { }
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/// impl<T: Bound + Specialize> Tr for T { }
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/// impl<T: Bound> Tr for T { }
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/// impl<T: ~const Bound + Specialize> const Tr for T { }
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/// ```
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fn trait_predicates_eq<'tcx>(
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predicate1: ty::Predicate<'tcx>,
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predicate2: ty::Predicate<'tcx>,
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@ -400,6 +425,8 @@ fn trait_predicates_eq<'tcx>(
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_ => kind,
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};
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// We rely on `check_constness` above to ensure that pred1 is const if pred2
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// is const.
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let pred1_kind_not_const = predicate1.kind().map_bound(predicate_kind_without_constness);
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let pred2_kind_not_const = predicate2.kind().map_bound(predicate_kind_without_constness);
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@ -1,5 +1,5 @@
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// Tests that a const default trait impl can be specialized by a non-const trait
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// impl, but that the specializing impl cannot be used in a const context.
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// Tests that a const default trait impl cannot be specialized by a non-const
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// trait impl.
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#![feature(const_trait_impl)]
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#![feature(min_specialization)]
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@ -8,12 +8,6 @@ trait Value {
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fn value() -> u32;
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}
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const fn get_value<T: ~const Value>() -> u32 {
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T::value()
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//~^ ERROR any use of this value will cause an error [const_err]
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//~| WARNING this was previously accepted
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}
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impl<T> const Value for T {
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default fn value() -> u32 {
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0
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@ -22,16 +16,11 @@ impl<T> const Value for T {
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struct FortyTwo;
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impl Value for FortyTwo {
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impl Value for FortyTwo { //~ ERROR cannot specialize on const impl with non-const impl
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fn value() -> u32 {
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println!("You can't do that (constly)");
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42
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}
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}
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const ZERO: u32 = get_value::<()>();
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const FORTY_TWO: u32 =
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get_value::<FortyTwo>(); // This is the line that causes the error, but it gets reported above
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fn main() {}
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@ -1,37 +1,8 @@
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error: any use of this value will cause an error
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--> $DIR/const-default-non-const-specialized.rs:12:5
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error: cannot specialize on const impl with non-const impl
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--> $DIR/const-default-non-const-specialized.rs:19:1
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LL | T::value()
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| ^^^^^^^^^^
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| |
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| calling non-const function `<FortyTwo as Value>::value`
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| inside `get_value::<FortyTwo>` at $DIR/const-default-non-const-specialized.rs:12:5
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| inside `FORTY_TWO` at $DIR/const-default-non-const-specialized.rs:35:5
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...
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LL | const FORTY_TWO: u32 =
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| --------------------
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= note: `#[deny(const_err)]` on by default
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= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
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= note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
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LL | impl Value for FortyTwo {
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| ^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to previous error
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Future incompatibility report: Future breakage diagnostic:
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error: any use of this value will cause an error
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--> $DIR/const-default-non-const-specialized.rs:12:5
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LL | T::value()
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| ^^^^^^^^^^
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| |
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| calling non-const function `<FortyTwo as Value>::value`
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| inside `get_value::<FortyTwo>` at $DIR/const-default-non-const-specialized.rs:12:5
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| inside `FORTY_TWO` at $DIR/const-default-non-const-specialized.rs:35:5
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...
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LL | const FORTY_TWO: u32 =
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| --------------------
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= note: `#[deny(const_err)]` on by default
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= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
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= note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
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@ -1,4 +1,4 @@
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// Tests that `T: ~const Foo` and `T: Foo` are treated as equivalent for the
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// Tests that `T: Foo` and `T: ~const Foo` are treated as equivalent for the
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// purposes of min_specialization.
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// check-pass
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@ -14,14 +14,14 @@ trait Foo {}
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trait Bar {}
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impl<T> const Bar for T
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where
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T: ~const Foo,
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{}
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impl<T> Bar for T
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where
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T: Foo,
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{}
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impl<T> const Bar for T
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where
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T: ~const Foo,
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T: Specialize,
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{}
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@ -1,6 +1,8 @@
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// Tests that a non-const default impl can be specialized by a const trait impl,
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// but that the default impl cannot be used in a const context.
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// run-pass
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#![feature(const_trait_impl)]
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#![feature(min_specialization)]
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@ -27,8 +29,10 @@ impl const Value for FortyTwo {
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}
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}
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const ZERO: u32 = get_value::<()>(); //~ ERROR the trait bound `(): ~const Value` is not satisfied
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fn main() {
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let zero = get_value::<()>();
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assert_eq!(zero, 0);
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const FORTY_TWO: u32 = get_value::<FortyTwo>();
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fn main() {}
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assert_eq!(FORTY_TWO, 42);
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}
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@ -1,20 +0,0 @@
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error[E0277]: the trait bound `(): ~const Value` is not satisfied
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--> $DIR/non-const-default-const-specialized.rs:30:31
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LL | const ZERO: u32 = get_value::<()>();
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| ^^ the trait `~const Value` is not implemented for `()`
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note: the trait `Value` is implemented for `()`, but that implementation is not `const`
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--> $DIR/non-const-default-const-specialized.rs:30:31
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LL | const ZERO: u32 = get_value::<()>();
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| ^^
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note: required by a bound in `get_value`
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--> $DIR/non-const-default-const-specialized.rs:11:23
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LL | const fn get_value<T: ~const Value>() -> u32 {
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| ^^^^^^^^^^^^ required by this bound in `get_value`
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error: aborting due to previous error
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For more information about this error, try `rustc --explain E0277`.
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