466 lines
18 KiB
Rust
466 lines
18 KiB
Rust
use rustc_errors::ErrorGuaranteed;
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use rustc_hir::def::DefKind;
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use rustc_hir::def_id::LocalDefId;
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use rustc_index::vec::IndexVec;
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use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
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use rustc_middle::ty::abstract_const::{CastKind, Node, NodeId};
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use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
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use rustc_middle::{mir, thir};
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use rustc_span::Span;
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use rustc_target::abi::VariantIdx;
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use std::iter;
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use crate::errors::{GenericConstantTooComplex, GenericConstantTooComplexSub};
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/// Destructures array, ADT or tuple constants into the constants
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/// of their fields.
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pub(crate) fn destructure_const<'tcx>(
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tcx: TyCtxt<'tcx>,
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const_: ty::Const<'tcx>,
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) -> ty::DestructuredConst<'tcx> {
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let ty::ConstKind::Value(valtree) = const_.kind() else {
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bug!("cannot destructure constant {:?}", const_)
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};
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let branches = match valtree {
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ty::ValTree::Branch(b) => b,
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_ => bug!("cannot destructure constant {:?}", const_),
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};
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let (fields, variant) = match const_.ty().kind() {
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ty::Array(inner_ty, _) | ty::Slice(inner_ty) => {
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// construct the consts for the elements of the array/slice
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let field_consts = branches
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.iter()
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.map(|b| tcx.mk_const(ty::ConstS { kind: ty::ConstKind::Value(*b), ty: *inner_ty }))
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.collect::<Vec<_>>();
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debug!(?field_consts);
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(field_consts, None)
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}
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ty::Adt(def, _) if def.variants().is_empty() => bug!("unreachable"),
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ty::Adt(def, substs) => {
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let (variant_idx, branches) = if def.is_enum() {
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let (head, rest) = branches.split_first().unwrap();
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(VariantIdx::from_u32(head.unwrap_leaf().try_to_u32().unwrap()), rest)
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} else {
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(VariantIdx::from_u32(0), branches)
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};
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let fields = &def.variant(variant_idx).fields;
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let mut field_consts = Vec::with_capacity(fields.len());
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for (field, field_valtree) in iter::zip(fields, branches) {
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let field_ty = field.ty(tcx, substs);
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let field_const = tcx.mk_const(ty::ConstS {
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kind: ty::ConstKind::Value(*field_valtree),
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ty: field_ty,
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});
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field_consts.push(field_const);
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}
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debug!(?field_consts);
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(field_consts, Some(variant_idx))
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}
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ty::Tuple(elem_tys) => {
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let fields = iter::zip(*elem_tys, branches)
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.map(|(elem_ty, elem_valtree)| {
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tcx.mk_const(ty::ConstS {
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kind: ty::ConstKind::Value(*elem_valtree),
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ty: elem_ty,
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})
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})
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.collect::<Vec<_>>();
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(fields, None)
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}
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_ => bug!("cannot destructure constant {:?}", const_),
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};
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let fields = tcx.arena.alloc_from_iter(fields.into_iter());
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ty::DestructuredConst { variant, fields }
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}
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pub struct AbstractConstBuilder<'a, 'tcx> {
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tcx: TyCtxt<'tcx>,
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body_id: thir::ExprId,
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body: &'a thir::Thir<'tcx>,
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/// The current WIP node tree.
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nodes: IndexVec<NodeId, Node<'tcx>>,
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}
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impl<'a, 'tcx> AbstractConstBuilder<'a, 'tcx> {
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fn root_span(&self) -> Span {
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self.body.exprs[self.body_id].span
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}
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fn error(&mut self, sub: GenericConstantTooComplexSub) -> Result<!, ErrorGuaranteed> {
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let reported = self.tcx.sess.emit_err(GenericConstantTooComplex {
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span: self.root_span(),
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maybe_supported: None,
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sub,
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});
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Err(reported)
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}
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fn maybe_supported_error(
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&mut self,
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sub: GenericConstantTooComplexSub,
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) -> Result<!, ErrorGuaranteed> {
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let reported = self.tcx.sess.emit_err(GenericConstantTooComplex {
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span: self.root_span(),
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maybe_supported: Some(()),
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sub,
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});
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Err(reported)
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}
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#[instrument(skip(tcx, body, body_id), level = "debug")]
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pub fn new(
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tcx: TyCtxt<'tcx>,
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(body, body_id): (&'a thir::Thir<'tcx>, thir::ExprId),
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) -> Result<Option<AbstractConstBuilder<'a, 'tcx>>, ErrorGuaranteed> {
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let builder = AbstractConstBuilder { tcx, body_id, body, nodes: IndexVec::new() };
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struct IsThirPolymorphic<'a, 'tcx> {
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is_poly: bool,
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thir: &'a thir::Thir<'tcx>,
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}
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use crate::rustc_middle::thir::visit::Visitor;
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use thir::visit;
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impl<'a, 'tcx> IsThirPolymorphic<'a, 'tcx> {
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fn expr_is_poly(&mut self, expr: &thir::Expr<'tcx>) -> bool {
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if expr.ty.has_param_types_or_consts() {
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return true;
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}
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match expr.kind {
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thir::ExprKind::NamedConst { substs, .. } => substs.has_param_types_or_consts(),
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thir::ExprKind::ConstParam { .. } => true,
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thir::ExprKind::Repeat { value, count } => {
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self.visit_expr(&self.thir()[value]);
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count.has_param_types_or_consts()
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}
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_ => false,
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}
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}
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fn pat_is_poly(&mut self, pat: &thir::Pat<'tcx>) -> bool {
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if pat.ty.has_param_types_or_consts() {
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return true;
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}
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match pat.kind.as_ref() {
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thir::PatKind::Constant { value } => value.has_param_types_or_consts(),
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thir::PatKind::Range(thir::PatRange { lo, hi, .. }) => {
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lo.has_param_types_or_consts() || hi.has_param_types_or_consts()
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}
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_ => false,
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}
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}
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}
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impl<'a, 'tcx> visit::Visitor<'a, 'tcx> for IsThirPolymorphic<'a, 'tcx> {
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fn thir(&self) -> &'a thir::Thir<'tcx> {
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&self.thir
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}
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#[instrument(skip(self), level = "debug")]
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fn visit_expr(&mut self, expr: &thir::Expr<'tcx>) {
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self.is_poly |= self.expr_is_poly(expr);
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if !self.is_poly {
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visit::walk_expr(self, expr)
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}
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}
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#[instrument(skip(self), level = "debug")]
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fn visit_pat(&mut self, pat: &thir::Pat<'tcx>) {
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self.is_poly |= self.pat_is_poly(pat);
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if !self.is_poly {
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visit::walk_pat(self, pat);
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}
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}
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}
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let mut is_poly_vis = IsThirPolymorphic { is_poly: false, thir: body };
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visit::walk_expr(&mut is_poly_vis, &body[body_id]);
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debug!("AbstractConstBuilder: is_poly={}", is_poly_vis.is_poly);
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if !is_poly_vis.is_poly {
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return Ok(None);
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}
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Ok(Some(builder))
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}
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/// We do not allow all binary operations in abstract consts, so filter disallowed ones.
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fn check_binop(op: mir::BinOp) -> bool {
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use mir::BinOp::*;
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match op {
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Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Shl | Shr | Eq | Lt | Le
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| Ne | Ge | Gt => true,
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Offset => false,
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}
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}
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/// While we currently allow all unary operations, we still want to explicitly guard against
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/// future changes here.
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fn check_unop(op: mir::UnOp) -> bool {
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use mir::UnOp::*;
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match op {
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Not | Neg => true,
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}
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}
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/// Builds the abstract const by walking the thir and bailing out when
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/// encountering an unsupported operation.
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pub fn build(mut self) -> Result<&'tcx [Node<'tcx>], ErrorGuaranteed> {
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debug!("AbstractConstBuilder::build: body={:?}", &*self.body);
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self.recurse_build(self.body_id)?;
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for n in self.nodes.iter() {
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if let Node::Leaf(ct) = n {
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if let ty::ConstKind::Unevaluated(ct) = ct.kind() {
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// `AbstractConst`s should not contain any promoteds as they require references which
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// are not allowed.
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assert_eq!(ct.promoted, None);
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assert_eq!(ct, self.tcx.erase_regions(ct));
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}
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}
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}
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Ok(self.tcx.arena.alloc_from_iter(self.nodes.into_iter()))
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}
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fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorGuaranteed> {
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use thir::ExprKind;
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let node = &self.body.exprs[node];
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Ok(match &node.kind {
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// I dont know if handling of these 3 is correct
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&ExprKind::Scope { value, .. } => self.recurse_build(value)?,
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&ExprKind::PlaceTypeAscription { source, .. }
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| &ExprKind::ValueTypeAscription { source, .. } => self.recurse_build(source)?,
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&ExprKind::Literal { lit, neg } => {
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let sp = node.span;
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let constant = match self.tcx.at(sp).lit_to_const(LitToConstInput {
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lit: &lit.node,
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ty: node.ty,
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neg,
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}) {
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Ok(c) => c,
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Err(LitToConstError::Reported) => self.tcx.const_error(node.ty),
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Err(LitToConstError::TypeError) => {
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bug!("encountered type error in lit_to_const")
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}
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};
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self.nodes.push(Node::Leaf(constant))
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}
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&ExprKind::NonHirLiteral { lit, user_ty: _ } => {
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let val = ty::ValTree::from_scalar_int(lit);
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self.nodes.push(Node::Leaf(ty::Const::from_value(self.tcx, val, node.ty)))
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}
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&ExprKind::ZstLiteral { user_ty: _ } => {
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let val = ty::ValTree::zst();
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self.nodes.push(Node::Leaf(ty::Const::from_value(self.tcx, val, node.ty)))
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}
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&ExprKind::NamedConst { def_id, substs, user_ty: _ } => {
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let uneval = ty::Unevaluated::new(ty::WithOptConstParam::unknown(def_id), substs);
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let constant = self
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.tcx
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.mk_const(ty::ConstS { kind: ty::ConstKind::Unevaluated(uneval), ty: node.ty });
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self.nodes.push(Node::Leaf(constant))
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}
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ExprKind::ConstParam { param, .. } => {
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let const_param = self
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.tcx
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.mk_const(ty::ConstS { kind: ty::ConstKind::Param(*param), ty: node.ty });
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self.nodes.push(Node::Leaf(const_param))
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}
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ExprKind::Call { fun, args, .. } => {
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let fun = self.recurse_build(*fun)?;
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let mut new_args = Vec::<NodeId>::with_capacity(args.len());
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for &id in args.iter() {
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new_args.push(self.recurse_build(id)?);
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}
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let new_args = self.tcx.arena.alloc_slice(&new_args);
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self.nodes.push(Node::FunctionCall(fun, new_args))
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}
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&ExprKind::Binary { op, lhs, rhs } if Self::check_binop(op) => {
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let lhs = self.recurse_build(lhs)?;
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let rhs = self.recurse_build(rhs)?;
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self.nodes.push(Node::Binop(op, lhs, rhs))
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}
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&ExprKind::Unary { op, arg } if Self::check_unop(op) => {
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let arg = self.recurse_build(arg)?;
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self.nodes.push(Node::UnaryOp(op, arg))
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}
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// This is necessary so that the following compiles:
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//
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// ```
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// fn foo<const N: usize>(a: [(); N + 1]) {
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// bar::<{ N + 1 }>();
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// }
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// ```
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ExprKind::Block { block } => {
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if let thir::Block { stmts: box [], expr: Some(e), .. } = &self.body.blocks[*block]
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{
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self.recurse_build(*e)?
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} else {
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self.maybe_supported_error(GenericConstantTooComplexSub::BlockNotSupported(
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node.span,
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))?
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}
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}
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// `ExprKind::Use` happens when a `hir::ExprKind::Cast` is a
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// "coercion cast" i.e. using a coercion or is a no-op.
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// This is important so that `N as usize as usize` doesnt unify with `N as usize`. (untested)
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&ExprKind::Use { source } => {
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let arg = self.recurse_build(source)?;
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self.nodes.push(Node::Cast(CastKind::Use, arg, node.ty))
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}
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&ExprKind::Cast { source } => {
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let arg = self.recurse_build(source)?;
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self.nodes.push(Node::Cast(CastKind::As, arg, node.ty))
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}
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ExprKind::Borrow { arg, .. } => {
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let arg_node = &self.body.exprs[*arg];
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// Skip reborrows for now until we allow Deref/Borrow/AddressOf
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// expressions.
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// FIXME(generic_const_exprs): Verify/explain why this is sound
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if let ExprKind::Deref { arg } = arg_node.kind {
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self.recurse_build(arg)?
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} else {
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self.maybe_supported_error(GenericConstantTooComplexSub::BorrowNotSupported(
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node.span,
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))?
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}
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}
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// FIXME(generic_const_exprs): We may want to support these.
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ExprKind::AddressOf { .. } | ExprKind::Deref { .. } => self.maybe_supported_error(
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GenericConstantTooComplexSub::AddressAndDerefNotSupported(node.span),
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)?,
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ExprKind::Repeat { .. } | ExprKind::Array { .. } => self.maybe_supported_error(
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GenericConstantTooComplexSub::ArrayNotSupported(node.span),
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)?,
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ExprKind::NeverToAny { .. } => self.maybe_supported_error(
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GenericConstantTooComplexSub::NeverToAnyNotSupported(node.span),
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)?,
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ExprKind::Tuple { .. } => self.maybe_supported_error(
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GenericConstantTooComplexSub::TupleNotSupported(node.span),
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)?,
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ExprKind::Index { .. } => self.maybe_supported_error(
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GenericConstantTooComplexSub::IndexNotSupported(node.span),
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)?,
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ExprKind::Field { .. } => self.maybe_supported_error(
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GenericConstantTooComplexSub::FieldNotSupported(node.span),
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)?,
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ExprKind::ConstBlock { .. } => self.maybe_supported_error(
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GenericConstantTooComplexSub::ConstBlockNotSupported(node.span),
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)?,
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ExprKind::Adt(_) => self
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.maybe_supported_error(GenericConstantTooComplexSub::AdtNotSupported(node.span))?,
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// dont know if this is correct
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ExprKind::Pointer { .. } => {
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self.error(GenericConstantTooComplexSub::PointerNotSupported(node.span))?
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}
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ExprKind::Yield { .. } => {
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self.error(GenericConstantTooComplexSub::YieldNotSupported(node.span))?
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}
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ExprKind::Continue { .. } | ExprKind::Break { .. } | ExprKind::Loop { .. } => {
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self.error(GenericConstantTooComplexSub::LoopNotSupported(node.span))?
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}
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ExprKind::Box { .. } => {
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self.error(GenericConstantTooComplexSub::BoxNotSupported(node.span))?
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}
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ExprKind::Unary { .. } => unreachable!(),
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// we handle valid unary/binary ops above
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ExprKind::Binary { .. } => {
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self.error(GenericConstantTooComplexSub::BinaryNotSupported(node.span))?
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}
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ExprKind::LogicalOp { .. } => {
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self.error(GenericConstantTooComplexSub::LogicalOpNotSupported(node.span))?
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}
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ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
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self.error(GenericConstantTooComplexSub::AssignNotSupported(node.span))?
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}
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ExprKind::Closure { .. } | ExprKind::Return { .. } => {
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self.error(GenericConstantTooComplexSub::ClosureAndReturnNotSupported(node.span))?
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}
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// let expressions imply control flow
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ExprKind::Match { .. } | ExprKind::If { .. } | ExprKind::Let { .. } => {
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self.error(GenericConstantTooComplexSub::ControlFlowNotSupported(node.span))?
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}
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ExprKind::InlineAsm { .. } => {
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self.error(GenericConstantTooComplexSub::InlineAsmNotSupported(node.span))?
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}
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// we dont permit let stmts so `VarRef` and `UpvarRef` cant happen
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ExprKind::VarRef { .. }
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| ExprKind::UpvarRef { .. }
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| ExprKind::StaticRef { .. }
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| ExprKind::ThreadLocalRef(_) => {
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self.error(GenericConstantTooComplexSub::OperationNotSupported(node.span))?
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}
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})
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}
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}
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/// Builds an abstract const, do not use this directly, but use `AbstractConst::new` instead.
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pub fn thir_abstract_const<'tcx>(
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tcx: TyCtxt<'tcx>,
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def: ty::WithOptConstParam<LocalDefId>,
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) -> Result<Option<&'tcx [Node<'tcx>]>, ErrorGuaranteed> {
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if tcx.features().generic_const_exprs {
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match tcx.def_kind(def.did) {
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// FIXME(generic_const_exprs): We currently only do this for anonymous constants,
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// meaning that we do not look into associated constants. I(@lcnr) am not yet sure whether
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// we want to look into them or treat them as opaque projections.
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//
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// Right now we do neither of that and simply always fail to unify them.
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DefKind::AnonConst | DefKind::InlineConst => (),
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_ => return Ok(None),
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}
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let body = tcx.thir_body(def)?;
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AbstractConstBuilder::new(tcx, (&*body.0.borrow(), body.1))?
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.map(AbstractConstBuilder::build)
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.transpose()
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} else {
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Ok(None)
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}
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}
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pub fn provide(providers: &mut ty::query::Providers) {
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*providers = ty::query::Providers {
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destructure_const,
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thir_abstract_const: |tcx, def_id| {
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let def_id = def_id.expect_local();
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if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
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tcx.thir_abstract_const_of_const_arg(def)
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} else {
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thir_abstract_const(tcx, ty::WithOptConstParam::unknown(def_id))
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}
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},
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thir_abstract_const_of_const_arg: |tcx, (did, param_did)| {
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thir_abstract_const(
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tcx,
|
|
ty::WithOptConstParam { did, const_param_did: Some(param_did) },
|
|
)
|
|
},
|
|
..*providers
|
|
};
|
|
}
|