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use std::ops::ControlFlow;
use super::{Byte, Def, Ref};
#[cfg(test)]
mod tests;
/// A tree-based representation of a type layout.
///
/// Invariants:
/// 1. All paths through the layout have the same length (in bytes).
///
/// Nice-to-haves:
/// 1. An `Alt` is never directly nested beneath another `Alt`.
/// 2. A `Seq` is never directly nested beneath another `Seq`.
/// 3. `Seq`s and `Alt`s with a single member do not exist.
#[derive(Clone, Debug, Hash, PartialEq, Eq)]
pub(crate) enum Tree<D, R>
where
D: Def,
R: Ref,
{
/// A sequence of successive layouts.
Seq(Vec<Self>),
/// A choice between alternative layouts.
Alt(Vec<Self>),
/// A definition node.
Def(D),
/// A reference node.
Ref(R),
/// A byte node.
Byte(Byte),
}
impl<D, R> Tree<D, R>
where
D: Def,
R: Ref,
{
/// A `Tree` consisting only of a definition node.
pub(crate) fn def(def: D) -> Self {
Self::Def(def)
}
/// A `Tree` representing an uninhabited type.
pub(crate) fn uninhabited() -> Self {
Self::Alt(vec![])
}
/// A `Tree` representing a zero-sized type.
pub(crate) fn unit() -> Self {
Self::Seq(Vec::new())
}
/// A `Tree` containing a single, uninitialized byte.
pub(crate) fn uninit() -> Self {
Self::Byte(Byte::Uninit)
}
/// A `Tree` representing the layout of `bool`.
pub(crate) fn bool() -> Self {
Self::from_bits(0x00).or(Self::from_bits(0x01))
}
/// A `Tree` whose layout matches that of a `u8`.
pub(crate) fn u8() -> Self {
Self::Alt((0u8..=255).map(Self::from_bits).collect())
}
/// A `Tree` whose layout accepts exactly the given bit pattern.
pub(crate) fn from_bits(bits: u8) -> Self {
Self::Byte(Byte::Init(bits))
}
/// A `Tree` whose layout is a number of the given width.
pub(crate) fn number(width_in_bytes: usize) -> Self {
Self::Seq(vec![Self::u8(); width_in_bytes])
}
/// A `Tree` whose layout is entirely padding of the given width.
pub(crate) fn padding(width_in_bytes: usize) -> Self {
Self::Seq(vec![Self::uninit(); width_in_bytes])
}
/// Remove all `Def` nodes, and all branches of the layout for which `f`
/// produces `true`.
pub(crate) fn prune<F>(self, f: &F) -> Tree<!, R>
where
F: Fn(D) -> bool,
{
match self {
Self::Seq(elts) => match elts.into_iter().map(|elt| elt.prune(f)).try_fold(
Tree::unit(),
|elts, elt| {
if elt == Tree::uninhabited() {
ControlFlow::Break(Tree::uninhabited())
} else {
ControlFlow::Continue(elts.then(elt))
}
},
) {
ControlFlow::Break(node) | ControlFlow::Continue(node) => node,
},
Self::Alt(alts) => alts
.into_iter()
.map(|alt| alt.prune(f))
.fold(Tree::uninhabited(), |alts, alt| alts.or(alt)),
Self::Byte(b) => Tree::Byte(b),
Self::Ref(r) => Tree::Ref(r),
Self::Def(d) => {
if f(d) {
Tree::uninhabited()
} else {
Tree::unit()
}
}
}
}
/// Produces `true` if `Tree` is an inhabited type; otherwise false.
pub(crate) fn is_inhabited(&self) -> bool {
match self {
Self::Seq(elts) => elts.into_iter().all(|elt| elt.is_inhabited()),
Self::Alt(alts) => alts.into_iter().any(|alt| alt.is_inhabited()),
Self::Byte(..) | Self::Ref(..) | Self::Def(..) => true,
}
}
}
impl<D, R> Tree<D, R>
where
D: Def,
R: Ref,
{
/// Produces a new `Tree` where `other` is sequenced after `self`.
pub(crate) fn then(self, other: Self) -> Self {
match (self, other) {
(Self::Seq(elts), other) | (other, Self::Seq(elts)) if elts.len() == 0 => other,
(Self::Seq(mut lhs), Self::Seq(mut rhs)) => {
lhs.append(&mut rhs);
Self::Seq(lhs)
}
(Self::Seq(mut lhs), rhs) => {
lhs.push(rhs);
Self::Seq(lhs)
}
(lhs, Self::Seq(mut rhs)) => {
rhs.insert(0, lhs);
Self::Seq(rhs)
}
(lhs, rhs) => Self::Seq(vec![lhs, rhs]),
}
}
/// Produces a new `Tree` accepting either `self` or `other` as alternative layouts.
pub(crate) fn or(self, other: Self) -> Self {
match (self, other) {
(Self::Alt(alts), other) | (other, Self::Alt(alts)) if alts.len() == 0 => other,
(Self::Alt(mut lhs), Self::Alt(rhs)) => {
lhs.extend(rhs);
Self::Alt(lhs)
}
(Self::Alt(mut alts), alt) | (alt, Self::Alt(mut alts)) => {
alts.push(alt);
Self::Alt(alts)
}
(lhs, rhs) => Self::Alt(vec![lhs, rhs]),
}
}
}
#[cfg(feature = "rustc")]
pub(crate) mod rustc {
use rustc_middle::ty::layout::{HasTyCtxt, LayoutCx, LayoutError};
use rustc_middle::ty::{self, AdtDef, AdtKind, List, ScalarInt, Ty, TyCtxt, TypeVisitableExt};
use rustc_span::ErrorGuaranteed;
use rustc_target::abi::{
FieldIdx, FieldsShape, Layout, Size, TyAndLayout, VariantIdx, Variants,
};
use super::Tree;
use crate::layout::rustc::{layout_of, Def, Ref};
#[derive(Debug, Copy, Clone)]
pub(crate) enum Err {
/// The layout of the type is not yet supported.
NotYetSupported,
/// This error will be surfaced elsewhere by rustc, so don't surface it.
UnknownLayout,
/// Overflow size
SizeOverflow,
TypeError(ErrorGuaranteed),
}
impl<'tcx> From<&LayoutError<'tcx>> for Err {
fn from(err: &LayoutError<'tcx>) -> Self {
match err {
LayoutError::Unknown(..) | LayoutError::ReferencesError(..) => Self::UnknownLayout,
LayoutError::SizeOverflow(..) => Self::SizeOverflow,
LayoutError::Cycle(err) => Self::TypeError(*err),
err => unimplemented!("{:?}", err),
}
}
}
impl<'tcx> Tree<Def<'tcx>, Ref<'tcx>> {
pub fn from_ty(ty: Ty<'tcx>, cx: LayoutCx<'tcx, TyCtxt<'tcx>>) -> Result<Self, Err> {
use rustc_target::abi::HasDataLayout;
let layout = layout_of(cx, ty)?;
if let Err(e) = ty.error_reported() {
return Err(Err::TypeError(e));
}
let target = cx.tcx.data_layout();
let pointer_size = target.pointer_size;
match ty.kind() {
ty::Bool => Ok(Self::bool()),
ty::Float(nty) => {
let width = nty.bit_width() / 8;
Ok(Self::number(width as _))
}
ty::Int(nty) => {
let width = nty.normalize(pointer_size.bits() as _).bit_width().unwrap() / 8;
Ok(Self::number(width as _))
}
ty::Uint(nty) => {
let width = nty.normalize(pointer_size.bits() as _).bit_width().unwrap() / 8;
Ok(Self::number(width as _))
}
ty::Tuple(members) => Self::from_tuple((ty, layout), members, cx),
ty::Array(inner_ty, len) => {
let FieldsShape::Array { stride, count } = &layout.fields else {
return Err(Err::NotYetSupported);
};
let inner_layout = layout_of(cx, *inner_ty)?;
assert_eq!(*stride, inner_layout.size);
let elt = Tree::from_ty(*inner_ty, cx)?;
Ok(std::iter::repeat(elt)
.take(*count as usize)
.fold(Tree::unit(), |tree, elt| tree.then(elt)))
}
ty::Adt(adt_def, _args_ref) if !ty.is_box() => match adt_def.adt_kind() {
AdtKind::Struct => Self::from_struct((ty, layout), *adt_def, cx),
AdtKind::Enum => Self::from_enum((ty, layout), *adt_def, cx),
AdtKind::Union => Self::from_union((ty, layout), *adt_def, cx),
},
ty::Ref(lifetime, ty, mutability) => {
let layout = layout_of(cx, *ty)?;
let align = layout.align.abi.bytes_usize();
let size = layout.size.bytes_usize();
Ok(Tree::Ref(Ref {
lifetime: *lifetime,
ty: *ty,
mutability: *mutability,
align,
size,
}))
}
_ => Err(Err::NotYetSupported),
}
}
/// Constructs a `Tree` from a tuple.
fn from_tuple(
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
members: &'tcx List<Ty<'tcx>>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
match &layout.fields {
FieldsShape::Primitive => {
assert_eq!(members.len(), 1);
let inner_ty = members[0];
let inner_layout = layout_of(cx, inner_ty)?;
Self::from_ty(inner_ty, cx)
}
FieldsShape::Arbitrary { offsets, .. } => {
assert_eq!(offsets.len(), members.len());
Self::from_variant(Def::Primitive, None, (ty, layout), layout.size, cx)
}
FieldsShape::Array { .. } | FieldsShape::Union(_) => Err(Err::NotYetSupported),
}
}
/// Constructs a `Tree` from a struct.
///
/// # Panics
///
/// Panics if `def` is not a struct definition.
fn from_struct(
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_struct());
let def = Def::Adt(def);
Self::from_variant(def, None, (ty, layout), layout.size, cx)
}
/// Constructs a `Tree` from an enum.
///
/// # Panics
///
/// Panics if `def` is not an enum definition.
fn from_enum(
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_enum());
// Computes the variant of a given index.
let layout_of_variant = |index| {
let tag = cx.tcx.tag_for_variant((cx.tcx.erase_regions(ty), index));
let variant_def = Def::Variant(def.variant(index));
let variant_layout = ty_variant(cx, (ty, layout), index);
Self::from_variant(variant_def, tag, (ty, variant_layout), layout.size, cx)
};
// We consider three kinds of enums, each demanding a different
// treatment of their layout computation:
// 1. enums that are uninhabited ZSTs
// 2. enums that delegate their layout to a variant
// 3. enums with multiple variants
match layout.variants() {
Variants::Single { .. }
if layout.abi.is_uninhabited() && layout.size == Size::ZERO =>
{
// The layout representation of uninhabited, ZST enums is
// defined to be like that of the `!` type, as opposed of a
// typical enum. Consequently, they cannot be descended into
// as if they typical enums. We therefore special-case this
// scenario and simply return an uninhabited `Tree`.
Ok(Self::uninhabited())
}
Variants::Single { index } => {
// `Variants::Single` on enums with variants denotes that
// the enum delegates its layout to the variant at `index`.
layout_of_variant(*index)
}
Variants::Multiple { tag_field, .. } => {
// `Variants::Multiple` denotes an enum with multiple
// variants. The layout of such an enum is the disjunction
// of the layouts of its tagged variants.
// For enums (but not coroutines), the tag field is
// currently always the first field of the layout.
assert_eq!(*tag_field, 0);
let variants = def.discriminants(cx.tcx()).try_fold(
Self::uninhabited(),
|variants, (idx, ref discriminant)| {
let variant = layout_of_variant(idx)?;
Result::<Self, Err>::Ok(variants.or(variant))
},
)?;
return Ok(Self::def(Def::Adt(def)).then(variants));
}
}
}
/// Constructs a `Tree` from a 'variant-like' layout.
///
/// A 'variant-like' layout includes those of structs and, of course,
/// enum variants. Pragmatically speaking, this method supports anything
/// with `FieldsShape::Arbitrary`.
///
/// Note: This routine assumes that the optional `tag` is the first
/// field, and enum callers should check that `tag_field` is, in fact,
/// `0`.
fn from_variant(
def: Def<'tcx>,
tag: Option<ScalarInt>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
total_size: Size,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
// This constructor does not support non-`FieldsShape::Arbitrary`
// layouts.
let FieldsShape::Arbitrary { offsets, memory_index } = layout.fields() else {
return Err(Err::NotYetSupported);
};
// When this function is invoked with enum variants,
// `ty_and_layout.size` does not encompass the entire size of the
// enum. We rely on `total_size` for this.
assert!(layout.size <= total_size);
let mut size = Size::ZERO;
let mut struct_tree = Self::def(def);
// If a `tag` is provided, place it at the start of the layout.
if let Some(tag) = tag {
size += tag.size();
struct_tree = struct_tree.then(Self::from_tag(tag, cx.tcx));
}
// Append the fields, in memory order, to the layout.
let inverse_memory_index = memory_index.invert_bijective_mapping();
for (memory_idx, &field_idx) in inverse_memory_index.iter_enumerated() {
// Add interfield padding.
let padding_needed = offsets[field_idx] - size;
let padding = Self::padding(padding_needed.bytes_usize());
let field_ty = ty_field(cx, (ty, layout), field_idx);
let field_layout = layout_of(cx, field_ty)?;
let field_tree = Self::from_ty(field_ty, cx)?;
struct_tree = struct_tree.then(padding).then(field_tree);
size += padding_needed + field_layout.size;
}
// Add trailing padding.
let padding_needed = total_size - size;
let trailing_padding = Self::padding(padding_needed.bytes_usize());
Ok(struct_tree.then(trailing_padding))
}
/// Constructs a `Tree` representing the value of a enum tag.
fn from_tag(tag: ScalarInt, tcx: TyCtxt<'tcx>) -> Self {
use rustc_target::abi::Endian;
let size = tag.size();
let bits = tag.to_bits(size);
let bytes: [u8; 16];
let bytes = match tcx.data_layout.endian {
Endian::Little => {
bytes = bits.to_le_bytes();
&bytes[..size.bytes_usize()]
}
Endian::Big => {
bytes = bits.to_be_bytes();
&bytes[bytes.len() - size.bytes_usize()..]
}
};
Self::Seq(bytes.iter().map(|&b| Self::from_bits(b)).collect())
}
/// Constructs a `Tree` from a union.
///
/// # Panics
///
/// Panics if `def` is not a union definition.
fn from_union(
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_union());
// This constructor does not support non-`FieldsShape::Union`
// layouts. Fields of this shape are all placed at offset 0.
let FieldsShape::Union(fields) = layout.fields() else {
return Err(Err::NotYetSupported);
};
let fields = &def.non_enum_variant().fields;
let fields = fields.iter_enumerated().try_fold(
Self::uninhabited(),
|fields, (idx, field_def)| {
let field_def = Def::Field(field_def);
let field_ty = ty_field(cx, (ty, layout), idx);
let field_layout = layout_of(cx, field_ty)?;
let field = Self::from_ty(field_ty, cx)?;
let trailing_padding_needed = layout.size - field_layout.size;
let trailing_padding = Self::padding(trailing_padding_needed.bytes_usize());
let field_and_padding = field.then(trailing_padding);
Result::<Self, Err>::Ok(fields.or(field_and_padding))
},
)?;
Ok(Self::def(Def::Adt(def)).then(fields))
}
}
fn ty_field<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
i: FieldIdx,
) -> Ty<'tcx> {
match ty.kind() {
ty::Adt(def, args) => {
match layout.variants {
Variants::Single { index } => {
let field = &def.variant(index).fields[i];
field.ty(cx.tcx, args)
}
// Discriminant field for enums (where applicable).
Variants::Multiple { tag, .. } => {
assert_eq!(i.as_usize(), 0);
ty::layout::PrimitiveExt::to_ty(&tag.primitive(), cx.tcx)
}
}
}
ty::Tuple(fields) => fields[i.as_usize()],
kind @ _ => unimplemented!(
"only a subset of `Ty::ty_and_layout_field`'s functionality is implemented. implementation needed for {:?}",
kind
),
}
}
fn ty_variant<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
i: VariantIdx,
) -> Layout<'tcx> {
let ty = cx.tcx.erase_regions(ty);
TyAndLayout { ty, layout }.for_variant(&cx, i).layout
}
}