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Use correct substs in enum discriminant cast #98429

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merged 5 commits into from
Jun 25, 2022
Merged

Use correct substs in enum discriminant cast #98429

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4c4fb71
add test
b-naber Jun 23, 2022
2e3221a
use correct substs in enum discriminant hack
b-naber Jun 23, 2022
38814fc
small refactor
b-naber Jun 24, 2022
f39c0d6
address review
b-naber Jun 24, 2022
bf48b62
fmt
b-naber Jun 24, 2022
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188 changes: 96 additions & 92 deletions compiler/rustc_mir_build/src/thir/cx/expr.rs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
use crate::thir::cx::region::Scope;
use crate::thir::cx::Cx;
use crate::thir::util::UserAnnotatedTyHelpers;
use rustc_data_structures::stack::ensure_sufficient_stack;
Expand Down Expand Up @@ -158,6 +159,100 @@ impl<'tcx> Cx<'tcx> {
Expr { temp_lifetime, ty: adjustment.target, span, kind }
}

/// Lowers a cast expression.
///
/// Dealing with user type annotations is left to the caller.
fn mirror_expr_cast(
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&mut self,
source: &'tcx hir::Expr<'tcx>,
temp_lifetime: Option<Scope>,
span: Span,
) -> ExprKind<'tcx> {
let tcx = self.tcx;

// Check to see if this cast is a "coercion cast", where the cast is actually done
// using a coercion (or is a no-op).
if self.typeck_results().is_coercion_cast(source.hir_id) {
// Convert the lexpr to a vexpr.
ExprKind::Use { source: self.mirror_expr(source) }
} else if self.typeck_results().expr_ty(source).is_region_ptr() {
// Special cased so that we can type check that the element
// type of the source matches the pointed to type of the
// destination.
ExprKind::Pointer {
source: self.mirror_expr(source),
cast: PointerCast::ArrayToPointer,
}
} 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 hir::ExprKind::Path(ref qpath) = source.kind else {
return ExprKind::Cast { source: self.mirror_expr(source)};
};

let res = self.typeck_results().qpath_res(qpath, source.hir_id);
let ty = self.typeck_results().node_type(source.hir_id);
let ty::Adt(adt_def, substs) = ty.kind() else {
return ExprKind::Cast { source: self.mirror_expr(source)};
};
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same here

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Do you mean the formatting here? As I said this is what x.py formats this to. We also don't get any tidy check failure.

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yes,

As I said this is what x.py formats this to. We also don't get any tidy check failure.

which is happening because rustfmt ignores let else for now. It just keeps the formatting from the user. You can change the formatting of let else to pretty much whatever you want and ./x.py fmt won't change it or complain

let Res::Def(
DefKind::Ctor(CtorOf::Variant, CtorKind::Const),
variant_ctor_id,
) = res else {
return ExprKind::Cast { source: self.mirror_expr(source)};
};
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@lcnr lcnr Jun 24, 2022 •
edited
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wrong indentation, rustfmt doesn't work for let else for now

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hm did call ./x.py fmt this time

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yes, but rustfmt does not work, you have to manually fix indentation for now


let idx = adt_def.variant_index_with_ctor_id(variant_ctor_id);
let (discr_did, discr_offset) = adt_def.discriminant_def_for_variant(idx);

use rustc_middle::ty::util::IntTypeExt;
let ty = adt_def.repr().discr_type();
let discr_ty = ty.to_ty(tcx);

let param_env_ty = self.param_env.and(discr_ty);
let size = tcx
.layout_of(param_env_ty)
.unwrap_or_else(|e| {
panic!("could not compute layout for {:?}: {:?}", param_env_ty, e)
})
.size;

let lit = ScalarInt::try_from_uint(discr_offset as u128, size).unwrap();
let kind = ExprKind::NonHirLiteral { lit, user_ty: None };
let offset = self.thir.exprs.push(Expr { temp_lifetime, ty: discr_ty, span, kind });

let source = match discr_did {
// in case we are offsetting from a computed discriminant
// and not the beginning of discriminants (which is always `0`)
Some(did) => {
let kind = ExprKind::NamedConst { def_id: did, substs, user_ty: None };
let lhs =
self.thir.exprs.push(Expr { temp_lifetime, ty: discr_ty, span, kind });
let bin = ExprKind::Binary { op: BinOp::Add, lhs, rhs: offset };
self.thir.exprs.push(Expr {
temp_lifetime,
ty: discr_ty,
span: span,
kind: bin,
})
}
None => offset,
};

ExprKind::Cast { source }
}
}

fn make_mirror_unadjusted(&mut self, expr: &'tcx hir::Expr<'tcx>) -> Expr<'tcx> {
let tcx = self.tcx;
let expr_ty = self.typeck_results().expr_ty(expr);
Expand Down Expand Up @@ -604,98 +699,7 @@ impl<'tcx> Cx<'tcx> {
expr, cast_ty.hir_id, user_ty,
);

// Check to see if this cast is a "coercion cast", where the cast is actually done
// using a coercion (or is a no-op).
let cast = if self.typeck_results().is_coercion_cast(source.hir_id) {
// Convert the lexpr to a vexpr.
ExprKind::Use { source: self.mirror_expr(source) }
} else if self.typeck_results().expr_ty(source).is_region_ptr() {
// Special cased so that we can type check that the element
// type of the source matches the pointed to type of the
// destination.
ExprKind::Pointer {
source: self.mirror_expr(source),
cast: PointerCast::ArrayToPointer,
}
} 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.kind {
let res = self.typeck_results().qpath_res(qpath, source.hir_id);
self.typeck_results().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_middle::ty::util::IntTypeExt;
let ty = adt_def.repr().discr_type();
let ty = ty.to_ty(tcx);
Some((d, o, ty))
}
_ => None,
},
)
} else {
None
};

let source = if let Some((did, offset, var_ty)) = var {
let param_env_ty = self.param_env.and(var_ty);
let size = tcx
.layout_of(param_env_ty)
.unwrap_or_else(|e| {
panic!("could not compute layout for {:?}: {:?}", param_env_ty, e)
})
.size;
let lit = ScalarInt::try_from_uint(offset as u128, size).unwrap();
let kind = ExprKind::NonHirLiteral { lit, user_ty: None };
let offset = self.thir.exprs.push(Expr {
temp_lifetime,
ty: var_ty,
span: expr.span,
kind,
});
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(tcx, did);
let kind =
ExprKind::NamedConst { def_id: did, substs, user_ty: None };
let lhs = self.thir.exprs.push(Expr {
temp_lifetime,
ty: var_ty,
span: expr.span,
kind,
});
let bin = ExprKind::Binary { op: BinOp::Add, lhs, rhs: offset };
self.thir.exprs.push(Expr {
temp_lifetime,
ty: var_ty,
span: expr.span,
kind: bin,
})
}
None => offset,
}
} else {
self.mirror_expr(source)
};

ExprKind::Cast { source: source }
};
let cast = self.mirror_expr_cast(*source, temp_lifetime, expr.span);

if let Some(user_ty) = user_ty {
// NOTE: Creating a new Expr and wrapping a Cast inside of it may be
Expand Down
10 changes: 10 additions & 0 deletions src/test/ui/const-generics/issues/issue-97634.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
//build-pass
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Suggested change
//build-pass
// build-pass


pub enum Register<const N: u16> {
Field0 = 40,
Field1,
}

fn main() {
let _b = Register::<0>::Field1 as u16;
}