Fix two minor issues in hir.rs
I found these two places in hir.rs which could use a bit of improvements while going through the code.
No functional change.
Put the incompatible_closure_captures lint messages in alphabetical order
Looks like they were in hash order before, which was causing me trouble in #94598, so this PR sorts the errors by trait name.
turn `append_place_to_string` from recursion into iteration
This PR fixes the FIXME in the impl of `append_place_to_string` which turns `append_place_to_string` from recursion into iteration, meanwhile simplifying the code relatively.
Collect function instance used in `global_asm!` sym operand
The constants used in SymFn operands have FnDef type,
so the type of the constant identifies the function.
Fixes#96623.
Allow inline consts to reference generic params
Tracking issue: #76001
The RFC says that inline consts cannot reference to generic parameters (for now), same as array length expressions. And expresses that it's desirable for it to reference in-scope generics, when array length expressions gain that feature as well.
However it is possible to implement this for inline consts before doing this for all anon consts, because inline consts are only used as values and they won't be used in the type system. So we can have:
```rust
fn foo<T>() {
let x = [4i32; std::mem::size_of::<T>()]; // NOT ALLOWED (for now)
let x = const { std::mem::size_of::<T>() }; // ALLOWED with this PR!
let x = [4i32; const { std::mem::size_of::<T>() }]; // NOT ALLOWED (for now)
}
```
This would make inline consts super useful for compile-time checks and assertions:
```rust
fn assert_zst<T>() {
const { assert!(std::mem::size_of::<T>() == 0) };
}
```
This would create an error during monomorphization when `assert_zst` is instantiated with non-ZST `T`s. A error during mono might sound scary, but this is exactly what a "desugared" inline const would do:
```rust
fn assert_zst<T>() {
struct F<T>(T);
impl<T> F<T> {
const V: () = assert!(std::mem::size_of::<T>() == 0);
}
let _ = F::<T>::V;
}
```
It should also be noted that the current inline const implementation can already reference the type params via type inference, so this resolver-level restriction is not any useful either:
```rust
fn foo<T>() -> usize {
let (_, size): (PhantomData<T>, usize) = const {
const fn my_size_of<T>() -> (PhantomData<T>, usize) {
(PhantomData, std::mem::size_of::<T>())
}
my_size_of()
};
size
}
```
```@rustbot``` label: F-inline_const
Fixing #95444 by only displaying passes that take more than 5 millise…
As discussed in #95444, I have added the code to test and only display prints that are greater than 5 milliseconds.
r? `@jyn514`
Remove mutable_borrow_reservation_conflict lint and allow the code pattern
This was the only breaking issue with the NLL stabilization PR. Lang team decided to go ahead and allow this.
r? `@nikomatsakis`
Closes#59159Closes#56254
Add a dedicated length-prefixing method to `Hasher`
This accomplishes two main goals:
- Make it clear who is responsible for prefix-freedom, including how they should do it
- Make it feasible for a `Hasher` that *doesn't* care about Hash-DoS resistance to get better performance by not hashing lengths
This does not change rustc-hash, since that's in an external crate, but that could potentially use it in future.
Fixes#94026
r? rust-lang/libs
---
The core of this change is the following two new methods on `Hasher`:
```rust
pub trait Hasher {
/// Writes a length prefix into this hasher, as part of being prefix-free.
///
/// If you're implementing [`Hash`] for a custom collection, call this before
/// writing its contents to this `Hasher`. That way
/// `(collection![1, 2, 3], collection![4, 5])` and
/// `(collection![1, 2], collection![3, 4, 5])` will provide different
/// sequences of values to the `Hasher`
///
/// The `impl<T> Hash for [T]` includes a call to this method, so if you're
/// hashing a slice (or array or vector) via its `Hash::hash` method,
/// you should **not** call this yourself.
///
/// This method is only for providing domain separation. If you want to
/// hash a `usize` that represents part of the *data*, then it's important
/// that you pass it to [`Hasher::write_usize`] instead of to this method.
///
/// # Examples
///
/// ```
/// #![feature(hasher_prefixfree_extras)]
/// # // Stubs to make the `impl` below pass the compiler
/// # struct MyCollection<T>(Option<T>);
/// # impl<T> MyCollection<T> {
/// # fn len(&self) -> usize { todo!() }
/// # }
/// # impl<'a, T> IntoIterator for &'a MyCollection<T> {
/// # type Item = T;
/// # type IntoIter = std::iter::Empty<T>;
/// # fn into_iter(self) -> Self::IntoIter { todo!() }
/// # }
///
/// use std:#️⃣:{Hash, Hasher};
/// impl<T: Hash> Hash for MyCollection<T> {
/// fn hash<H: Hasher>(&self, state: &mut H) {
/// state.write_length_prefix(self.len());
/// for elt in self {
/// elt.hash(state);
/// }
/// }
/// }
/// ```
///
/// # Note to Implementers
///
/// If you've decided that your `Hasher` is willing to be susceptible to
/// Hash-DoS attacks, then you might consider skipping hashing some or all
/// of the `len` provided in the name of increased performance.
#[inline]
#[unstable(feature = "hasher_prefixfree_extras", issue = "88888888")]
fn write_length_prefix(&mut self, len: usize) {
self.write_usize(len);
}
/// Writes a single `str` into this hasher.
///
/// If you're implementing [`Hash`], you generally do not need to call this,
/// as the `impl Hash for str` does, so you can just use that.
///
/// This includes the domain separator for prefix-freedom, so you should
/// **not** call `Self::write_length_prefix` before calling this.
///
/// # Note to Implementers
///
/// The default implementation of this method includes a call to
/// [`Self::write_length_prefix`], so if your implementation of `Hasher`
/// doesn't care about prefix-freedom and you've thus overridden
/// that method to do nothing, there's no need to override this one.
///
/// This method is available to be overridden separately from the others
/// as `str` being UTF-8 means that it never contains `0xFF` bytes, which
/// can be used to provide prefix-freedom cheaper than hashing a length.
///
/// For example, if your `Hasher` works byte-by-byte (perhaps by accumulating
/// them into a buffer), then you can hash the bytes of the `str` followed
/// by a single `0xFF` byte.
///
/// If your `Hasher` works in chunks, you can also do this by being careful
/// about how you pad partial chunks. If the chunks are padded with `0x00`
/// bytes then just hashing an extra `0xFF` byte doesn't necessarily
/// provide prefix-freedom, as `"ab"` and `"ab\u{0}"` would likely hash
/// the same sequence of chunks. But if you pad with `0xFF` bytes instead,
/// ensuring at least one padding byte, then it can often provide
/// prefix-freedom cheaper than hashing the length would.
#[inline]
#[unstable(feature = "hasher_prefixfree_extras", issue = "88888888")]
fn write_str(&mut self, s: &str) {
self.write_length_prefix(s.len());
self.write(s.as_bytes());
}
}
```
With updates to the `Hash` implementations for slices and containers to call `write_length_prefix` instead of `write_usize`.
`write_str` defaults to using `write_length_prefix` since, as was pointed out in the issue, the `write_u8(0xFF)` approach is insufficient for hashers that work in chunks, as those would hash `"a\u{0}"` and `"a"` to the same thing. But since `SipHash` works byte-wise (there's an internal buffer to accumulate bytes until a full chunk is available) it overrides `write_str` to continue to use the add-non-UTF-8-byte approach.
---
Compatibility:
Because the default implementation of `write_length_prefix` calls `write_usize`, the changed hash implementation for slices will do the same thing the old one did on existing `Hasher`s.
This accomplishes two main goals:
- Make it clear who is responsible for prefix-freedom, including how they should do it
- Make it feasible for a `Hasher` that *doesn't* care about Hash-DoS resistance to get better performance by not hashing lengths
This does not change rustc-hash, since that's in an external crate, but that could potentially use it in future.
Currently, the only API for creating errors from a diagnostic derive
will emit it immediately. This makes it difficult to add subdiagnostics
to diagnostics from the derive, so add `create_{err,warning}` functions
that return the diagnostic without emitting it.
Signed-off-by: David Wood <david.wood@huawei.com>
Diagnostics can have multiple primary spans, or have subdiagnostics
repeated at multiple locations, so support `Vec<..>` fields in the
diagnostic derive which become loops in the generated code.
Signed-off-by: David Wood <david.wood@huawei.com>
95444: Adding passes that include memory increase
Fix95444: Change the substraction with the abs_diff() method
Fix95444: Change the substraction with abs_diff() method
Fixes#96319
The logic around handling co-inductive cycles in the evaluation cache
is confusing and error prone. Fortunately, a perf run showed that it
doesn't actually appear to improve performance, so we can simplify
this code (and eliminate a source of ICEs) by just skipping caching
the evaluation results for co-inductive cycle participants.
This commit makes no changes to any of the other logic around
co-inductive cycle handling. Thus, while this commit could
potentially expose latent bugs that were being hidden by
caching, it should not introduce any new bugs.
interpret/validity: debug-check ScalarPair layout information
This would have caught https://github.com/rust-lang/rust/issues/96158.
I ran the Miri test suite and it still passes.
r? `@oli-obk`
Report that opaque types are not allowed in impls even in the presence of other errors
fixes #96569
before this PR those useful errors were hidden because either `unused parameter` or `only traits defined in the current crate can be implemented for arbitrary types` got emitted first.
Add a new Rust attribute to support embedding debugger visualizers
Implemented [this RFC](https://github.com/rust-lang/rfcs/pull/3191) to add support for embedding debugger visualizers into a PDB.
Added a new attribute `#[debugger_visualizer]` and updated the `CrateMetadata` to store debugger visualizers for crate dependencies.
RFC: https://github.com/rust-lang/rfcs/pull/3191
do not suggest when trait_ref is some
Update compiler/rustc_resolve/src/late/diagnostics.rs
Co-authored-by: lcnr <rust@lcnr.de>
use helper struct
add a test for functions with some params
refactor debug log
Enable tracing for all queries
This allows you to log everything within a specific query, e.g.
```
env RUSTC_LOG=[mir_borrowck]
```
dumping all borrowck queries may be a bit verbose, so you can also restrict it to just an item of your choice:
```
env RUSTC_LOG=[mir_borrowck{key=\.\*name_of_item\.\*}]
```
the regex `.*` in the key name are because the key is a debug printed DefId, so you'd get all kinds of things like hashes in there. The tracing logs will show you the key, so you can restrict it further if you want.
Revert "Prefer projection candidates instead of param_env candidates for Sized predicates"
Fixes#93262Reopens#89352
This was a hack that seemed to have no negative side-effects at the time. Given that the latter has a workaround and likely less common than the former, it makes sense to revert this change.
r? `@compiler-errors`
Overhaul `MacArgs`
Motivation:
- Clarify some code that I found hard to understand.
- Eliminate one use of three places where `TokenKind::Interpolated` values are created.
r? `@petrochenkov`
The value in `MacArgs::Eq` is currently represented as a `Token`.
Because of `TokenKind::Interpolated`, `Token` can be either a token or
an arbitrary AST fragment. In practice, a `MacArgs::Eq` starts out as a
literal or macro call AST fragment, and then is later lowered to a
literal token. But this is very non-obvious. `Token` is a much more
general type than what is needed.
This commit restricts things, by introducing a new type `MacArgsEqKind`
that is either an AST expression (pre-lowering) or an AST literal
(post-lowering). The downside is that the code is a bit more verbose in
a few places. The benefit is that makes it much clearer what the
possibilities are (though also shorter in some other places). Also, it
removes one use of `TokenKind::Interpolated`, taking us a step closer to
removing that variant, which will let us make `Token` impl `Copy` and
remove many "handle Interpolated" code paths in the parser.
Things to note:
- Error messages have improved. Messages like this:
```
unexpected token: `"bug" + "found"`
```
now say "unexpected expression", which makes more sense. Although
arbitrary expressions can exist within tokens thanks to
`TokenKind::Interpolated`, that's not obvious to anyone who doesn't
know compiler internals.
- In `parse_mac_args_common`, we no longer need to collect tokens for
the value expression.
Update `ProjectionElem::Downcast` documentation
`ProjectionElem:::Downcast` is used when downcasting to a variant of
an enum or a generator, regardless of the number of variants.
Quick fix for #96223.
This PR is a quick fix regarding #96223.
As mentioned in the issue, others modification could be added to not elide types with bound vars from suggestions.
Special thanks to ``@jackh726`` for mentoring and ``@Manishearth`` for minimal test case.
r? ``@jackh726``
When suggesting to import an item, also suggest changing the path if appropriate
When we don't find an item we search all of them for an appropriate
import and suggest `use`ing it. This is sometimes done for expressions
that have paths with more than one segment. We now also suggest changing
that path to work with the `use`.
Fix#95413
The comment on this function explains that it's a specialized version of
`maybe_whole_expr`. But `maybe_whole_expr` doesn't do anything with
`NtIdent`, so `is_whole_expr` also doesn't need to.
Cleanup `DebuggerVisualizerFile` type and other minor cleanup of queries.
Merge the queries for debugger visualizers into a single query.
Revert move of `resolve_path` to `rustc_builtin_macros`. Update dependencies in Cargo.toml for `rustc_passes`.
Respond to PR comments. Load visualizer files into opaque bytes `Vec<u8>`. Debugger visualizers for dynamically linked crates should not be embedded in the current crate.
Update the unstable book with the new feature. Add the tracking issue for the debugger_visualizer feature.
Respond to PR comments and minor cleanups.
Use reverse postorder in `non_ssa_locals`
The reverse postorder, unlike preorder, is now cached inside the MIR
body. Code generation uses reverse postorder anyway, so it might be
a small perf improvement to use it here as well.
Mitigate impact of subtle invalid call suggestion logic
There's some subtle interaction between inferred expressions being
passed as an argument to fn calls with fewer than expected arguments. To
avoid the ICE, I'm changing indexing operations with `.get(idx)`, but
the underlying logic still needs to be audited as it was written with
the assumption that `final_arg_types` and `provided_args` have the right
length.
Address #96638.
Update `RValue::Discriminant` documentation
`RValue::Discriminant` returns zero for types without discriminant.
This guarantee is already documented for `discriminant_value`
intrinsics which is implemented in terms of `RValue::Discriminant`.
Use source callsite in check_argument_types suggestion
This makes the "remove extra arguement" suggestion valid when the function argument is a macro.
Additionally, this may fix#96225, but the only way I can reproduce that issue is using the playground, so we will need to wait until after this is merged to ensure it's fixed.
Refactor the WriteBackendMethods and ExtraBackendMethods traits
The new interface is slightly less confusing and is easier to implement for non-LLVM backends.
When we don't find an item we search all of them for an appropriate
import and suggest `use`ing it. This is sometimes done for expressions
that have paths with more than one segment. We now also suggest changing
that path to work with the `use`.
Fix#95413
There's some subtle interaction between inferred expressions being
passed as an argument to fn calls with fewer than expected arguments. To
avoid the ICE, I'm changing indexing operations with `.get(idx)`, but
the underlying logic still needs to be audited as it was written with
the assumption that `final_arg_types` and `provided_args` have the right
length.
Address 96638.
Fix -Zdump-mir-dataflow by implementing DebugWithContext for ChunkedBitSet
`DebugWithContext` is used to format changes to dataflow state along with MIR
in graphviz dot files. In the case of `ChunkedBitSet` it was left unimplemented,
so attempts to use `-Zdump-mir-dataflow -Zdump-mir=all` resulted in an ICE:
> thread 'rustc' panicked at 'not implemented: implement when/if needed',
Provide the missing implementation.
r? `@nnethercote`
rustc: Panic by default in `DefIdTree::parent`
Only crate root def-ids don't have a parent, and in majority of cases the argument of `DefIdTree::parent` cannot be a crate root.
So we now panic by default in `parent` and introduce a new non-panicing function `opt_parent` for cases where the argument can be a crate root.
Same applies to `local_parent`/`opt_local_parent`.
Only crate root def-ids don't have a parent, and in majority of cases the argument of `DefIdTree::parent` cannot be a crate root.
So we now panic by default in `parent` and introduce a new non-panicing function `opt_parent` for cases where the argument can be a crate root.
Same applies to `local_parent`/`opt_local_parent`.
rustdoc: Resolve doc links referring to `macro_rules` items
cc https://github.com/rust-lang/rust/issues/81633
UPD: the fallback to considering *all* `macro_rules` in the crate for unresolved names is not removed in this PR, it will be removed separately and will be run through crater.
The reverse postorder, unlike preorder, is now cached inside the MIR
body. Code generation uses reverse postorder anyway, so it might be
a small perf improvement to use it here as well.
Also report the call site of PME errors locally.
Note this does not produce a full stack all the way to the first call that specifies all monomorphic parameters, it's just shallowly mentioning the last call site.
previous work: https://github.com/rust-lang/rust/pull/85633
tracking issue: https://github.com/rust-lang/rust/issues/85155
r? `@lqd`
I figured we could get some improvement for traces in local crates without going into the backtrace hell you landed in last time
`RValue::Discriminant` returns zero for types without discriminant.
This guarantee is already documented for `discriminant_value`
intrinsics which is implemented in terms of `RValue::Discriminant`.
Using an obviously-placeholder syntax. An RFC would still be needed before this could have any chance at stabilization, and it might be removed at any point.
But I'd really like to have it in nightly at least to ensure it works well with try_trait_v2, especially as we refactor the traits.
Erase type params when suggesting fully qualified path
When suggesting the use of a fully qualified path for a method call that
is ambiguous because it has multiple candidates, erase type params in
the resulting code, as they would result in an error when applied. We
replace them with `_` in the output to rely on inference. There might be
cases where this still produces slighlty incomplete suggestions, but it
otherwise produces many more errors in relatively common cases.
Fix#96292
Note this does not produce a full stack all the way to the first call that specifies all monomorphic parameters, it's just shallowly mentioning the last call site.
Enforce static lifetimes in consts during late resolution
This PR moves the handling of implicitly and explicitly static lifetimes in constants from HIR to the AST.
Reduce duplication of RPO calculation of mir
Computing the RPO of mir is not a low-cost thing, but it is duplicate in many places. In particular the `iterate_to_fixpoint` method which is called multiple times when computing the data flow.
This PR reduces the number of times the RPO is recalculated as much as possible, which should save some compile time.
Fix duplicate directory separator in --remap-path-prefix.
The compiler will currently emit duplicate directory separators when `--remap-path-prefix` has an exact match of the working directory and it is invoked with a relative path to the main source file. For example
```bash
rustc src/main.rs -Cdebuginfo=2 --remap-path-prefix="$(pwd)=abc"
```
will produce the path `abc//src/main.rs` in debuginfo. This is because `some_path.join("")` will append a directory separator to `some_path` and then LLVM does not check if the working directory already ends a directory separator before concatenating it with the relative path.
RustWrapper: explicitly don't handle DXILPointerTyID
This new enum entry was introduced in https://reviews.llvm.org/D122268,
and if I'm reading correctly there's no case where we'd ever encounter
it in our uses of LLVM. To preserve the ability to compile this file
with -Werror -Wswitch we add an explicit case for this entry.
r? nikic
Enforce Copy bounds for repeat elements while considering lifetimes
fixes https://github.com/rust-lang/rust/issues/95477
this is a breaking change in order to fix a soundness bug.
Before this PR we only checked whether the repeat element type had an `impl Copy`, but not whether that impl also had the appropriate lifetimes. E.g. if the impl was for `YourType<'static>` and not a general `'a`, then copying any type other than a `'static` one should have been rejected, but wasn't.
r? `@lcnr`
macros: subdiagnostic derive
Add a new macro, `#[derive(SessionSubdiagnostic)]`, which can be applied to structs that represent subdiagnostics, such as labels, notes, helps or suggestions.
`#[derive(SessionSubdiagnostic)]` can be used with the existing `#[derive(SessionDiagnostic)]`. All diagnostics implemented using either derive are translatable, and this new derive should make it easier to port existing diagnostics to using these derives.
For example, consider the following subdiagnostic types...
```rust
#[derive(SessionSubdiagnostic)]
pub enum ExpectedIdentifierLabel<'tcx> {
#[label(slug = "parser-expected-identifier")]
WithoutFound {
#[primary_span]
span: Span,
}
#[label(slug = "parser-expected-identifier-found")]
WithFound {
#[primary_span]
span: Span,
found: String,
}
}
#[derive(SessionSubdiagnostic)]
#[suggestion_verbose(slug = "parser-raw-identifier")]
pub struct RawIdentifierSuggestion<'tcx> {
#[primary_span]
span: Span,
#[applicability]
applicability: Applicability,
ident: Ident,
}
```
...and the corresponding Fluent messages:
```fluent
parser-expected-identifier = expected identifier
parser-expected-identifier-found = expected identifier, found {$found}
parser-raw-identifier = escape `{$ident}` to use it as an identifier
```
These can be emitted using the new `subdiagnostic` function on `Diagnostic`...
```rust
diag.subdiagnostic(ExpectedIdentifierLabel::WithoutFound { span });
diag.subdiagnostic(RawIdentifierSuggestion { span, applicability, ident });
```
...or as part of a larger `#[derive(SessionDiagnostic)]`:
```rust
#[derive(SessionDiagnostic)]
#[error(slug = "parser-expected-identifier")]
pub struct ExpectedIdentifier {
#[primary_span]
span: Span,
token_descr: String,
#[subdiagnostic]
label: ExpectedIdentifierLabel,
#[subdiagnostic]
raw_identifier_suggestion: Option<RawIdentifierSuggestion>,
}
```
```rust
sess.emit_err(ExpectedIdentifier { ... });
```
r? `@oli-obk`
cc `@pvdrz`
Revert diagnostic duplication and accidental stabilization
fixes#96460
this is an accidental stabilization that we should put into the beta. I believe it is low-risk, because it was literally what we had before #94081
The effect on tests is massive, but mostly deduplication of diagnostics and some minor span changes.
Update data layout string for wasm64-unknown-unknown
Looks like this changed in a recent LLVM update but wasm64 isn't built
on CI so it wasn't caught until now.
Closes#96463
The two paths are equivalent -- they both end up calling `visit_expr()`.
I have kept the more restrictive path, the one that requires that
`token` be an expression nonterminal. (The next commit will simplify this
function further.)
`make_tokenstream` has three commented hacks, and a comment at the top
referring to #67062. These hacks have no observable effect, at least as judged
by running the test suite. The hacks were added in #82608, with an explanation
[here](https://github.com/rust-lang/rust/pull/82608#issuecomment-812877329). It
appears that one of the following is true: (a) they never did anything useful,
(b) they do something useful but we have no test coverage for them, or (c)
something has changed in the meantime that means they are no longer necessary.
This commit removes the hacks and the comments, in the hope that (b) is not
true.
The `token` is always an interpolated non-terminal expression, and
always a literal in valid code. This commit simplifies the processing
accordingly, by directly extracting and using the literal.
This commit rearranges the `match`. The new code avoids testing for
`MacArgs::Eq` twice, at the cost of repeating the `self.print_path()`
call. I think this is worthwhile because it puts the `match` in a more
standard and readable form.
Add `#[subdiagnostic]` field attribute to the diagnostic derive which
is applied to fields that have types which use the subdiagnostic derive.
Signed-off-by: David Wood <david.wood@huawei.com>
In the initial implementation of the `SessionSubdiagnostic`, the
`Applicability` of a suggestion can be set both as a field and as part
of the attribute, this commit adds the same support to the original
`SessionDiagnostic` derive.
Signed-off-by: David Wood <david.wood@huawei.com>
`SetOnce` trait was introduced in the subdiagnostic derive to simplify
the code a little bit, re-use it in the diagnostic derive too.
Signed-off-by: David Wood <david.wood@huawei.com>
Remove some duplicated code between both diagnostic derives by
introducing helper functions for reporting an error in case of a invalid
attribute.
Signed-off-by: David Wood <david.wood@huawei.com>
Split `SessionDiagnostic` and `SessionSubdiagnostic` derives and the
various helper functions into multiple modules.
Signed-off-by: David Wood <david.wood@huawei.com>
Add a new derive, `#[derive(SessionSubdiagnostic)]`, which enables
deriving structs for labels, notes, helps and suggestions.
Signed-off-by: David Wood <david.wood@huawei.com>
Change `span_suggestion` (and variants) to take `impl ToString` rather
than `String` for the suggested code, as this simplifies the
requirements on the diagnostic derive.
Signed-off-by: David Wood <david.wood@huawei.com>
rustc_ast: Harmonize delimiter naming with `proc_macro::Delimiter`
Compiler cannot reuse `proc_macro::Delimiter` directly due to extra impls, but can at least use the same naming.
After this PR the only difference between these two enums is that `proc_macro::Delimiter::None` is turned into `token::Delimiter::Invisible`.
It's my mistake that the invisible delimiter is called `None` on stable, during the stabilization I audited the naming and wrote the docs, but missed the fact that the `None` naming gives a wrong and confusing impression about what this thing is.
cc https://github.com/rust-lang/rust/pull/96421
r? ``@nnethercote``
This new enum entry was introduced in https://reviews.llvm.org/D122268,
and if I'm reading correctly there's no case where we'd ever encounter
it in our uses of LLVM. To preserve the ability to compile this file
with -Werror -Wswitch we add an explicit case for this entry.
Implement Valtree to ConstValue conversion
Once we start to use `ValTree`s in the type system we will need to be able to convert them into `ConstValue` instances, which we want to continue to use after MIR construction.
r? `@oli-obk`
cc `@RalfJung`
