Work around a resolve bug in const prop
r? @wesleywiser @anp
This isn't exposed right now, but further changes to rustc may start causing bugs without this.
We only want to return specializations when `Reveal::All` is passed, not
when `Reveal::UserFacing` is. Resolving this fixes several issues with
the `ConstProp`, `SimplifyBranches`, and `Inline` MIR optimization
passes.
Fixes#66901
Various const eval and pattern matching ICE fixes
r? @RalfJung
cc @spastorino
This PR does not change existing behaviour anymore and just fixes a bunch of ICEs reachable from user code (sometimes even on stable via obscure union transmutes).
Add simpler entry points to const eval for common usages.
I found the `tcx.const_eval` API to be complex/awkward to work with, because of the inherent complexity from all of the different situations it is called from. Though it mainly used in one of the following ways:
- Evaluates the value of a constant without any substitutions, e.g. evaluating a static, discriminant, etc.
- Evaluates the value of a resolved instance of a constant. this happens when evaluating unevaluated constants or normalising trait constants.
- Evaluates a promoted constant.
This PR adds three new functions `const_eval_mono`, `const_eval_resolve`, and `const_eval_promoted` to `TyCtxt`, which each cater to one of the three ways `tcx.const_eval`
is normally used.
Cleanup `lower_pattern_unadjusted` & Improve slice pat typeck
Following up on https://github.com/rust-lang/rust/pull/67318, in this PR, the HAIR lowering of patterns (`lower_pattern_unadjusted`) is cleaned up with a focus on slice patterns (in particular, some dead code is removed). Moreover, `check_pat_slice` is refactored some more.
r? @matthewjasper
After #62550, it is no longer possible for `slice`
to be other than `None | Some(Binding(..) | Wild)`.
In particular, `lower_pat_slice` may never generate
`Some(Array(..) | Slice(..))` and so there is nothing
to flatten into `slice`.
The code is dead because `check_pat_slice` will never have
`expected = ty::Ref(...)` due to default-binding-modes
(see `is_non_ref_pat`, `peel_off_references`).
Moreover, if the type is not `ty::Array(_) | ty::Slice(_)`
then `check_pat_slice` enters an error branch.
Refactor slice pattern usefulness checking
As a follow up to https://github.com/rust-lang/rust/pull/65874, this PR changes how variable-length slice patterns are handled in usefulness checking. The objectives are: cleaning up that code to make it easier to understand, and paving the way to handling fixed-length slices more cleverly too, for https://github.com/rust-lang/rust/issues/53820.
Before this, variable-length slice patterns were eagerly expanded into a union of fixed-length slices. Now they have their own special constructor, which allows expanding them a bit more lazily.
As a nice side-effect, this improves diagnostics.
This PR shows a slight performance improvement, mostly due to 149792b608. This will probably have to be reverted in some way when we implement or-patterns.
(Or more precisely, a pair of such traits: one for `derive(PartialEq)` and one
for `derive(Eq)`.)
((The addition of the second marker trait, `StructuralEq`, is largely a hack to
work-around `fn (&T)` not implementing `PartialEq` and `Eq`; see also issue
rust-lang/rust#46989; otherwise I would just check if `Eq` is implemented.))
Note: this does not use trait fulfillment error-reporting machinery; it just
uses the trait system to determine if the ADT was tagged or not. (Nonetheless, I
have kept an `on_unimplemented` message on the new trait for structural_match
check, even though it is currently not used.)
Note also: this does *not* resolve the ICE from rust-lang/rust#65466, as noted
in a comment added in this commit. Further work is necessary to resolve that and
other problems with the structural match checking, especially to do so without
breaking stable code (adapted from test fn-ptr-is-structurally-matchable.rs):
```rust
fn r_sm_to(_: &SM) {}
fn main() {
const CFN6: Wrap<fn(&SM)> = Wrap(r_sm_to);
let input: Wrap<fn(&SM)> = Wrap(r_sm_to);
match Wrap(input) {
Wrap(CFN6) => {}
Wrap(_) => {}
};
}
```
where we would hit a problem with the strategy of unconditionally checking for
`PartialEq` because the type `for <'a> fn(&'a SM)` does not currently even
*implement* `PartialEq`.
----
added review feedback:
* use an or-pattern
* eschew `return` when tail position will do.
* don't need fresh_expansion; just add `structural_match` to appropriate `allow_internal_unstable` attributes.
also fixed example in doc comment so that it actually compiles.
Mazdak Farrokhzad
Vadim Petrochenkov
bors
Camille GILLOT
Wesley Wiser
Oliver Scherer
Mark Rousskov
Ben Lewis
varkor
Guillaume Gomez
Esteban Küber
Nadrieril
Felix S. Klock II
Yuki Okushi
Shotaro Yamada
csmoe