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Rollup merge of #133610 - camelid:move-from_anon_const, r=BoxyUwU

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Move `Const::{from_anon_const,try_from_lit}` to hir_ty_lowering

Fixes #128176.
This accomplishes one of the followup items from #131081.

These operations are much more about lowering the HIR than about
`Const`s themselves. They fit better in hir_ty_lowering with
`lower_const_arg` (formerly `Const::from_const_arg`) and the rest.

To accomplish this, `const_evaluatable_predicates_of` had to be changed
to not use `from_anon_const` anymore. Instead of visiting the HIR and
lowering anon consts on the fly, it now visits the `rustc_middle::ty`
data structures instead and directly looks for `UnevaluatedConst`s. This
approach was proposed in:
https://github.com/rust-lang/rust/pull/131081#discussion_r1821189257

r? `@BoxyUwU`
This commit is contained in:
Guillaume Gomez 2024-12-02 23:08:54 +01:00 • committed by GitHub
commit 6f0d15a144
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11 changed files with 245 additions and 168 deletions
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84
compiler/rustc_middle/src/ty/consts.rs
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@ -2,15 +2,11 @@ use std::borrow::Cow;
use rustc_data_structures::intern::Interned;
use rustc_error_messages::MultiSpan;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::LocalDefId;
use rustc_hir::{self as hir};
use rustc_macros::HashStable;
use rustc_type_ir::{self as ir, TypeFlags, WithCachedTypeInfo};
use tracing::{debug, instrument};
use crate::mir::interpret::{LitToConstInput, Scalar};
use crate::ty::{self, GenericArgs, Ty, TyCtxt, TypeVisitableExt};
use crate::mir::interpret::Scalar;
use crate::ty::{self, Ty, TyCtxt};
mod int;
mod kind;
@ -181,82 +177,6 @@ impl<'tcx> rustc_type_ir::inherent::Const<TyCtxt<'tcx>> for Const<'tcx> {
}
impl<'tcx> Const<'tcx> {
// FIXME: move this and try_from_lit to hir_ty_lowering like lower_const_arg/from_const_arg
/// Literals and const generic parameters are eagerly converted to a constant, everything else
/// becomes `Unevaluated`.
#[instrument(skip(tcx), level = "debug")]
pub fn from_anon_const(tcx: TyCtxt<'tcx>, def: LocalDefId) -> Self {
let body_id = match tcx.hir_node_by_def_id(def) {
hir::Node::AnonConst(ac) => ac.body,
node => span_bug!(
tcx.def_span(def.to_def_id()),
"from_anon_const can only process anonymous constants, not {node:?}"
),
};
let expr = &tcx.hir().body(body_id).value;
debug!(?expr);
let ty = tcx.type_of(def).no_bound_vars().expect("const parameter types cannot be generic");
match Self::try_from_lit(tcx, ty, expr) {
Some(v) => v,
None => ty::Const::new_unevaluated(tcx, ty::UnevaluatedConst {
def: def.to_def_id(),
args: GenericArgs::identity_for_item(tcx, def.to_def_id()),
}),
}
}
#[instrument(skip(tcx), level = "debug")]
fn try_from_lit(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, expr: &'tcx hir::Expr<'tcx>) -> Option<Self> {
// Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
// currently have to be wrapped in curly brackets, so it's necessary to special-case.
let expr = match &expr.kind {
hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
block.expr.as_ref().unwrap()
}
_ => expr,
};
if let hir::ExprKind::Path(hir::QPath::Resolved(
_,
&hir::Path { res: Res::Def(DefKind::ConstParam, _), .. },
)) = expr.kind
{
span_bug!(expr.span, "try_from_lit: received const param which shouldn't be possible");
};
let lit_input = match expr.kind {
hir::ExprKind::Lit(lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
hir::ExprKind::Unary(hir::UnOp::Neg, expr) => match expr.kind {
hir::ExprKind::Lit(lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: true }),
_ => None,
},
_ => None,
};
if let Some(lit_input) = lit_input {
// If an error occurred, ignore that it's a literal and leave reporting the error up to
// mir.
match tcx.at(expr.span).lit_to_const(lit_input) {
Ok(c) => return Some(c),
Err(_) if lit_input.ty.has_aliases() => {
// allow the `ty` to be an alias type, though we cannot handle it here
return None;
}
Err(e) => {
tcx.dcx().span_delayed_bug(
expr.span,
format!("Const::try_from_lit: couldn't lit_to_const {e:?}"),
);
}
}
}
None
}
/// Creates a constant with the given integer value and interns it.
#[inline]
pub fn from_bits(