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[DO NOT MERGE] see what breaks when we remove this recursive-enum-discriminants hack #61723

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[DO NOT MERGE] see what breaks when we remove this recursive-enum-discriminants hack #61723

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83 changes: 2 additions & 81 deletions src/librustc_mir/hair/cx/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use crate::hair::cx::block;
use crate::hair::cx::to_ref::ToRef;
use crate::hair::util::UserAnnotatedTyHelpers;
use rustc_data_structures::indexed_vec::Idx;
use rustc::hir::def::{CtorOf, Res, DefKind, CtorKind};
use rustc::hir::def::{Res, DefKind, CtorKind};
use rustc::mir::interpret::{GlobalId, ErrorHandled, ConstValue};
use rustc::ty::{self, AdtKind, Ty};
use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow, AutoBorrowMutability, PointerCast};
Expand Down Expand Up @@ -633,86 +633,7 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
// Convert the lexpr to a vexpr.
ExprKind::Use { source: source.to_ref() }
} else {
// check whether this is casting an enum variant discriminant
// to prevent cycles, we refer to the discriminant initializer
// which is always an integer and thus doesn't need to know the
// enum's layout (or its tag type) to compute it during const eval
// Example:
// enum Foo {
// A,
// B = A as isize + 4,
// }
// The correct solution would be to add symbolic computations to miri,
// so we wouldn't have to compute and store the actual value
let var = if let hir::ExprKind::Path(ref qpath) = source.node {
let res = cx.tables().qpath_res(qpath, source.hir_id);
cx
.tables()
.node_type(source.hir_id)
.ty_adt_def()
.and_then(|adt_def| {
match res {
Res::Def(
DefKind::Ctor(CtorOf::Variant, CtorKind::Const),
variant_ctor_id,
) => {
let idx = adt_def.variant_index_with_ctor_id(variant_ctor_id);
let (d, o) = adt_def.discriminant_def_for_variant(idx);
use rustc::ty::util::IntTypeExt;
let ty = adt_def.repr.discr_type();
let ty = ty.to_ty(cx.tcx());
Some((d, o, ty))
}
_ => None,
}
})
} else {
None
};

let source = if let Some((did, offset, var_ty)) = var {
let mk_const = |literal| Expr {
temp_lifetime,
ty: var_ty,
span: expr.span,
kind: ExprKind::Literal {
literal,
user_ty: None
},
}.to_ref();
let offset = mk_const(ty::Const::from_bits(
cx.tcx,
offset as u128,
cx.param_env.and(var_ty),
));
match did {
Some(did) => {
// in case we are offsetting from a computed discriminant
// and not the beginning of discriminants (which is always `0`)
let substs = InternalSubsts::identity_for_item(cx.tcx(), did);
let lhs = mk_const(cx.tcx().mk_const(ty::Const {
val: ConstValue::Unevaluated(did, substs),
ty: var_ty,
}));
let bin = ExprKind::Binary {
op: BinOp::Add,
lhs,
rhs: offset,
};
Expr {
temp_lifetime,
ty: var_ty,
span: expr.span,
kind: bin,
}.to_ref()
},
None => offset,
}
} else {
source.to_ref()
};

ExprKind::Cast { source }
ExprKind::Cast { source: source.to_ref() }
};

if let Some(user_ty) = user_ty {
Expand Down