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use super::{ErrorHandled, EvalToConstValueResult, EvalToValTreeResult, GlobalId};
use crate::mir;
use crate::query::{TyCtxtAt, TyCtxtEnsure};
use crate::ty::visit::TypeVisitableExt;
use crate::ty::GenericArgs;
use crate::ty::{self, TyCtxt};
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_session::lint;
use rustc_span::{Span, DUMMY_SP};
impl<'tcx> TyCtxt<'tcx> {
/// Evaluates a constant without providing any substitutions. This is useful to evaluate consts
/// that can't take any generic arguments like statics, const items or enum discriminants. If a
/// generic parameter is used within the constant `ErrorHandled::ToGeneric` will be returned.
#[instrument(skip(self), level = "debug")]
pub fn const_eval_poly(self, def_id: DefId) -> EvalToConstValueResult<'tcx> {
// In some situations def_id will have substitutions within scope, but they aren't allowed
// to be used. So we can't use `Instance::mono`, instead we feed unresolved substitutions
// into `const_eval` which will return `ErrorHandled::ToGeneric` if any of them are
// encountered.
let args = GenericArgs::identity_for_item(self, def_id);
let instance = ty::Instance::new(def_id, args);
let cid = GlobalId { instance, promoted: None };
let param_env = self.param_env(def_id).with_reveal_all_normalized(self);
self.const_eval_global_id(param_env, cid, None)
}
/// Resolves and evaluates a constant.
///
/// The constant can be located on a trait like `<A as B>::C`, in which case the given
/// substitutions and environment are used to resolve the constant. Alternatively if the
/// constant has generic parameters in scope the substitutions are used to evaluate the value of
/// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
/// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
/// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
/// returned.
#[instrument(level = "debug", skip(self))]
pub fn const_eval_resolve(
self,
param_env: ty::ParamEnv<'tcx>,
ct: mir::UnevaluatedConst<'tcx>,
span: Option<Span>,
) -> EvalToConstValueResult<'tcx> {
// Cannot resolve `Unevaluated` constants that contain inference
// variables. We reject those here since `resolve`
// would fail otherwise.
//
// When trying to evaluate constants containing inference variables,
// use `Infcx::const_eval_resolve` instead.
if ct.args.has_non_region_infer() {
bug!("did not expect inference variables here");
}
match ty::Instance::resolve(
self, param_env,
// FIXME: maybe have a separate version for resolving mir::UnevaluatedConst?
ct.def, ct.args,
) {
Ok(Some(instance)) => {
let cid = GlobalId { instance, promoted: ct.promoted };
self.const_eval_global_id(param_env, cid, span)
}
// For errors during resolution, we deliberately do not point at the usage site of the constant,
// since for these errors the place the constant is used shouldn't matter.
Ok(None) => Err(ErrorHandled::TooGeneric(DUMMY_SP)),
Err(err) => Err(ErrorHandled::Reported(err.into(), DUMMY_SP)),
}
}
#[instrument(level = "debug", skip(self))]
pub fn const_eval_resolve_for_typeck(
self,
param_env: ty::ParamEnv<'tcx>,
ct: ty::UnevaluatedConst<'tcx>,
span: Option<Span>,
) -> EvalToValTreeResult<'tcx> {
// Cannot resolve `Unevaluated` constants that contain inference
// variables. We reject those here since `resolve`
// would fail otherwise.
//
// When trying to evaluate constants containing inference variables,
// use `Infcx::const_eval_resolve` instead.
if ct.args.has_non_region_infer() {
bug!("did not expect inference variables here");
}
match ty::Instance::resolve(self, param_env, ct.def, ct.args) {
Ok(Some(instance)) => {
let cid = GlobalId { instance, promoted: None };
self.const_eval_global_id_for_typeck(param_env, cid, span).inspect(|_| {
// We are emitting the lint here instead of in `is_const_evaluatable`
// as we normalize obligations before checking them, and normalization
// uses this function to evaluate this constant.
//
// @lcnr believes that successfully evaluating even though there are
// used generic parameters is a bug of evaluation, so checking for it
// here does feel somewhat sensible.
if !self.features().generic_const_exprs && ct.args.has_non_region_param() {
let def_kind = self.def_kind(instance.def_id());
assert!(
matches!(
def_kind,
DefKind::InlineConst | DefKind::AnonConst | DefKind::AssocConst
),
"{cid:?} is {def_kind:?}",
);
let mir_body = self.mir_for_ctfe(instance.def_id());
if mir_body.is_polymorphic {
let Some(local_def_id) = ct.def.as_local() else { return };
self.struct_span_lint_hir(
lint::builtin::CONST_EVALUATABLE_UNCHECKED,
self.hir().local_def_id_to_hir_id(local_def_id),
self.def_span(ct.def),
"cannot use constants which depend on generic parameters in types",
|err| err,
)
}
}
})
}
// For errors during resolution, we deliberately do not point at the usage site of the constant,
// since for these errors the place the constant is used shouldn't matter.
Ok(None) => Err(ErrorHandled::TooGeneric(DUMMY_SP)),
Err(err) => Err(ErrorHandled::Reported(err.into(), DUMMY_SP)),
}
}
pub fn const_eval_instance(
self,
param_env: ty::ParamEnv<'tcx>,
instance: ty::Instance<'tcx>,
span: Option<Span>,
) -> EvalToConstValueResult<'tcx> {
self.const_eval_global_id(param_env, GlobalId { instance, promoted: None }, span)
}
/// Evaluate a constant to a `ConstValue`.
#[instrument(skip(self), level = "debug")]
pub fn const_eval_global_id(
self,
param_env: ty::ParamEnv<'tcx>,
cid: GlobalId<'tcx>,
span: Option<Span>,
) -> EvalToConstValueResult<'tcx> {
// Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
// improve caching of queries.
let inputs = self.erase_regions(param_env.and(cid));
if let Some(span) = span {
// The query doesn't know where it is being invoked, so we need to fix the span.
self.at(span).eval_to_const_value_raw(inputs).map_err(|e| e.with_span(span))
} else {
self.eval_to_const_value_raw(inputs)
}
}
/// Evaluate a constant to a type-level constant.
#[instrument(skip(self), level = "debug")]
pub fn const_eval_global_id_for_typeck(
self,
param_env: ty::ParamEnv<'tcx>,
cid: GlobalId<'tcx>,
span: Option<Span>,
) -> EvalToValTreeResult<'tcx> {
// Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
// improve caching of queries.
let inputs = self.erase_regions(param_env.and(cid));
debug!(?inputs);
if let Some(span) = span {
// The query doesn't know where it is being invoked, so we need to fix the span.
self.at(span).eval_to_valtree(inputs).map_err(|e| e.with_span(span))
} else {
self.eval_to_valtree(inputs)
}
}
/// Evaluate a static's initializer, returning the allocation of the initializer's memory.
#[inline(always)]
pub fn eval_static_initializer(
self,
def_id: DefId,
) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
self.at(DUMMY_SP).eval_static_initializer(def_id)
}
}
impl<'tcx> TyCtxtAt<'tcx> {
/// Evaluate a static's initializer, returning the allocation of the initializer's memory.
///
/// The span is entirely ignored here, but still helpful for better query cycle errors.
pub fn eval_static_initializer(
self,
def_id: DefId,
) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
trace!("eval_static_initializer: Need to compute {:?}", def_id);
assert!(self.is_static(def_id));
let instance = ty::Instance::mono(*self, def_id);
let gid = GlobalId { instance, promoted: None };
self.eval_to_allocation(gid, ty::ParamEnv::reveal_all())
}
/// Evaluate anything constant-like, returning the allocation of the final memory.
///
/// The span is entirely ignored here, but still helpful for better query cycle errors.
fn eval_to_allocation(
self,
gid: GlobalId<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
trace!("eval_to_allocation: Need to compute {:?}", gid);
let raw_const = self.eval_to_allocation_raw(param_env.and(gid))?;
Ok(self.global_alloc(raw_const.alloc_id).unwrap_memory())
}
}
impl<'tcx> TyCtxtEnsure<'tcx> {
/// Evaluates a constant without providing any substitutions. This is useful to evaluate consts
/// that can't take any generic arguments like statics, const items or enum discriminants. If a
/// generic parameter is used within the constant `ErrorHandled::ToGeneric` will be returned.
#[instrument(skip(self), level = "debug")]
pub fn const_eval_poly(self, def_id: DefId) {
// In some situations def_id will have substitutions within scope, but they aren't allowed
// to be used. So we can't use `Instance::mono`, instead we feed unresolved substitutions
// into `const_eval` which will return `ErrorHandled::ToGeneric` if any of them are
// encountered.
let args = GenericArgs::identity_for_item(self.tcx, def_id);
let instance = ty::Instance::new(def_id, args);
let cid = GlobalId { instance, promoted: None };
let param_env = self.tcx.param_env(def_id).with_reveal_all_normalized(self.tcx);
// Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
// improve caching of queries.
let inputs = self.tcx.erase_regions(param_env.and(cid));
self.eval_to_const_value_raw(inputs)
}
/// Evaluate a static's initializer, returning the allocation of the initializer's memory.
pub fn eval_static_initializer(self, def_id: DefId) {
trace!("eval_static_initializer: Need to compute {:?}", def_id);
assert!(self.tcx.is_static(def_id));
let instance = ty::Instance::mono(self.tcx, def_id);
let gid = GlobalId { instance, promoted: None };
let param_env = ty::ParamEnv::reveal_all();
trace!("eval_to_allocation: Need to compute {:?}", gid);
self.eval_to_allocation_raw(param_env.and(gid))
}
}