rustc_transmute/lib.rs
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// tidy-alphabetical-start
#![allow(unused_variables)]
#![feature(alloc_layout_extra)]
#![feature(never_type)]
#![warn(unreachable_pub)]
// tidy-alphabetical-end
pub(crate) use rustc_data_structures::fx::{FxIndexMap as Map, FxIndexSet as Set};
pub mod layout;
mod maybe_transmutable;
#[derive(Copy, Clone, Debug, Default)]
pub struct Assume {
pub alignment: bool,
pub lifetimes: bool,
pub safety: bool,
pub validity: bool,
}
/// Either transmutation is allowed, we have an error, or we have an optional
/// Condition that must hold.
#[derive(Debug, Hash, Eq, PartialEq, Clone)]
pub enum Answer<R> {
Yes,
No(Reason<R>),
If(Condition<R>),
}
/// A condition which must hold for safe transmutation to be possible.
#[derive(Debug, Hash, Eq, PartialEq, Clone)]
pub enum Condition<R> {
/// `Src` is transmutable into `Dst`, if `src` is transmutable into `dst`.
IfTransmutable { src: R, dst: R },
/// `Src` is transmutable into `Dst`, if all of the enclosed requirements are met.
IfAll(Vec<Condition<R>>),
/// `Src` is transmutable into `Dst` if any of the enclosed requirements are met.
IfAny(Vec<Condition<R>>),
}
/// Answers "why wasn't the source type transmutable into the destination type?"
#[derive(Debug, Hash, Eq, PartialEq, PartialOrd, Ord, Clone)]
pub enum Reason<T> {
/// The layout of the source type is not yet supported.
SrcIsNotYetSupported,
/// The layout of the destination type is not yet supported.
DstIsNotYetSupported,
/// The layout of the destination type is bit-incompatible with the source type.
DstIsBitIncompatible,
/// The destination type is uninhabited.
DstUninhabited,
/// The destination type may carry safety invariants.
DstMayHaveSafetyInvariants,
/// `Dst` is larger than `Src`, and the excess bytes were not exclusively uninitialized.
DstIsTooBig,
/// A referent of `Dst` is larger than a referent in `Src`.
DstRefIsTooBig {
/// The referent of the source type.
src: T,
/// The too-large referent of the destination type.
dst: T,
},
/// Src should have a stricter alignment than Dst, but it does not.
DstHasStricterAlignment { src_min_align: usize, dst_min_align: usize },
/// Can't go from shared pointer to unique pointer
DstIsMoreUnique,
/// Encountered a type error
TypeError,
/// The layout of src is unknown
SrcLayoutUnknown,
/// The layout of dst is unknown
DstLayoutUnknown,
/// The size of src is overflow
SrcSizeOverflow,
/// The size of dst is overflow
DstSizeOverflow,
}
#[cfg(feature = "rustc")]
mod rustc {
use rustc_hir::lang_items::LangItem;
use rustc_infer::infer::InferCtxt;
use rustc_macros::TypeVisitable;
use rustc_middle::traits::ObligationCause;
use rustc_middle::ty::{Const, ParamEnv, Ty, TyCtxt, ValTree};
use rustc_span::DUMMY_SP;
use super::*;
/// The source and destination types of a transmutation.
#[derive(TypeVisitable, Debug, Clone, Copy)]
pub struct Types<'tcx> {
/// The source type.
pub src: Ty<'tcx>,
/// The destination type.
pub dst: Ty<'tcx>,
}
pub struct TransmuteTypeEnv<'cx, 'tcx> {
infcx: &'cx InferCtxt<'tcx>,
}
impl<'cx, 'tcx> TransmuteTypeEnv<'cx, 'tcx> {
pub fn new(infcx: &'cx InferCtxt<'tcx>) -> Self {
Self { infcx }
}
#[allow(unused)]
pub fn is_transmutable(
&mut self,
cause: ObligationCause<'tcx>,
types: Types<'tcx>,
assume: crate::Assume,
) -> crate::Answer<crate::layout::rustc::Ref<'tcx>> {
crate::maybe_transmutable::MaybeTransmutableQuery::new(
types.src,
types.dst,
assume,
self.infcx.tcx,
)
.answer()
}
}
impl Assume {
/// Constructs an `Assume` from a given const-`Assume`.
pub fn from_const<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
c: Const<'tcx>,
) -> Option<Self> {
use rustc_middle::ty::ScalarInt;
use rustc_span::symbol::sym;
let Ok((ty, cv)) = c.eval(tcx, param_env, DUMMY_SP) else {
return Some(Self {
alignment: true,
lifetimes: true,
safety: true,
validity: true,
});
};
let adt_def = ty.ty_adt_def()?;
assert_eq!(
tcx.require_lang_item(LangItem::TransmuteOpts, None),
adt_def.did(),
"The given `Const` was not marked with the `{}` lang item.",
LangItem::TransmuteOpts.name(),
);
let variant = adt_def.non_enum_variant();
let fields = match cv {
ValTree::Branch(branch) => branch,
_ => {
return Some(Self {
alignment: true,
lifetimes: true,
safety: true,
validity: true,
});
}
};
let get_field = |name| {
let (field_idx, _) = variant
.fields
.iter()
.enumerate()
.find(|(_, field_def)| name == field_def.name)
.unwrap_or_else(|| panic!("There were no fields named `{name}`."));
fields[field_idx].unwrap_leaf() == ScalarInt::TRUE
};
Some(Self {
alignment: get_field(sym::alignment),
lifetimes: get_field(sym::lifetimes),
safety: get_field(sym::safety),
validity: get_field(sym::validity),
})
}
}
}
#[cfg(feature = "rustc")]
pub use rustc::*;