1 use crate::mir::interpret::LitToConstInput;
2 use crate::ty::{self, DefIdTree, InternalSubsts, ParamEnv, ParamEnvAnd, Ty, TyCtxt};
3 use rustc_data_structures::intern::Interned;
5 use rustc_hir::def_id::{DefId, LocalDefId};
6 use rustc_macros::HashStable;
17 /// Use this rather than `ConstS`, whenever possible.
18 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, HashStable)]
19 #[rustc_pass_by_value]
20 pub struct Const<'tcx>(pub Interned<'tcx, ConstS<'tcx>>);
22 impl<'tcx> fmt::Debug for Const<'tcx> {
23 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
24 // This reflects what `Const` looked liked before `Interned` was
25 // introduced. We print it like this to avoid having to update expected
26 // output in a lot of tests.
27 write!(f, "Const {{ ty: {:?}, kind: {:?} }}", self.ty(), self.kind())
31 /// Typed constant value.
32 #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, HashStable, TyEncodable, TyDecodable)]
33 pub struct ConstS<'tcx> {
35 pub kind: ConstKind<'tcx>,
38 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
39 static_assert_size!(ConstS<'_>, 40);
41 impl<'tcx> Const<'tcx> {
43 pub fn ty(self) -> Ty<'tcx> {
48 pub fn kind(self) -> ConstKind<'tcx> {
52 /// Literals and const generic parameters are eagerly converted to a constant, everything else
53 /// becomes `Unevaluated`.
54 pub fn from_anon_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
55 Self::from_opt_const_arg_anon_const(tcx, ty::WithOptConstParam::unknown(def_id))
58 #[instrument(skip(tcx), level = "debug")]
59 pub fn from_opt_const_arg_anon_const(
61 def: ty::WithOptConstParam<LocalDefId>,
63 let body_id = match tcx.hir().get_by_def_id(def.did) {
64 hir::Node::AnonConst(ac) => ac.body,
66 tcx.def_span(def.did.to_def_id()),
67 "from_anon_const can only process anonymous constants"
71 let expr = &tcx.hir().body(body_id).value;
74 let ty = tcx.type_of(def.def_id_for_type_of());
76 match Self::try_eval_lit_or_param(tcx, ty, expr) {
79 ty::ConstKind::Unevaluated(ty::UnevaluatedConst {
81 substs: InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
88 #[instrument(skip(tcx), level = "debug")]
89 fn try_eval_lit_or_param(
92 expr: &'tcx hir::Expr<'tcx>,
94 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
95 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
96 let expr = match &expr.kind {
97 hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
98 block.expr.as_ref().unwrap()
103 let lit_input = match expr.kind {
104 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
105 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => match expr.kind {
106 hir::ExprKind::Lit(ref lit) => {
107 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
114 if let Some(lit_input) = lit_input {
115 // If an error occurred, ignore that it's a literal and leave reporting the error up to
117 match tcx.at(expr.span).lit_to_const(lit_input) {
118 Ok(c) => return Some(c),
120 tcx.sess.delay_span_bug(
122 &format!("Const::from_anon_const: couldn't lit_to_const {:?}", e),
128 use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
130 ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
131 // Find the name and index of the const parameter by indexing the generics of
132 // the parent item and construct a `ParamConst`.
133 let item_def_id = tcx.parent(def_id);
134 let generics = tcx.generics_of(item_def_id);
135 let index = generics.param_def_id_to_index[&def_id];
136 let name = tcx.item_name(def_id);
137 Some(tcx.mk_const(ty::ConstKind::Param(ty::ParamConst::new(index, name)), ty))
143 /// Interns the given value as a constant.
145 pub fn from_value(tcx: TyCtxt<'tcx>, val: ty::ValTree<'tcx>, ty: Ty<'tcx>) -> Self {
146 tcx.mk_const(ConstKind::Value(val), ty)
149 /// Panics if self.kind != ty::ConstKind::Value
150 pub fn to_valtree(self) -> ty::ValTree<'tcx> {
152 ty::ConstKind::Value(valtree) => valtree,
153 _ => bug!("expected ConstKind::Value, got {:?}", self.kind()),
157 pub fn from_scalar_int(tcx: TyCtxt<'tcx>, i: ScalarInt, ty: Ty<'tcx>) -> Self {
158 let valtree = ty::ValTree::from_scalar_int(i);
159 Self::from_value(tcx, valtree, ty)
163 /// Creates a constant with the given integer value and interns it.
164 pub fn from_bits(tcx: TyCtxt<'tcx>, bits: u128, ty: ParamEnvAnd<'tcx, Ty<'tcx>>) -> Self {
167 .unwrap_or_else(|e| panic!("could not compute layout for {:?}: {:?}", ty, e))
169 Self::from_scalar_int(tcx, ScalarInt::try_from_uint(bits, size).unwrap(), ty.value)
173 /// Creates an interned zst constant.
174 pub fn zero_sized(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
175 let valtree = ty::ValTree::zst();
176 Self::from_value(tcx, valtree, ty)
180 /// Creates an interned bool constant.
181 pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> Self {
182 Self::from_bits(tcx, v as u128, ParamEnv::empty().and(tcx.types.bool))
186 /// Creates an interned usize constant.
187 pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> Self {
188 Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
192 /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
193 /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
194 /// contains const generic parameters or pointers).
195 pub fn try_eval_bits(
198 param_env: ParamEnv<'tcx>,
201 assert_eq!(self.ty(), ty);
202 let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;
203 // if `ty` does not depend on generic parameters, use an empty param_env
204 self.kind().eval(tcx, param_env).try_to_bits(size)
208 pub fn try_eval_bool(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
209 self.kind().eval(tcx, param_env).try_to_bool()
213 pub fn try_eval_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<u64> {
214 self.kind().eval(tcx, param_env).try_to_machine_usize(tcx)
218 /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the
219 /// unevaluated constant.
220 pub fn eval(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Const<'tcx> {
221 if let Some(val) = self.kind().try_eval_for_typeck(tcx, param_env) {
223 Ok(val) => Const::from_value(tcx, val, self.ty()),
224 Err(guar) => tcx.const_error_with_guaranteed(self.ty(), guar),
227 // Either the constant isn't evaluatable or ValTree creation failed.
233 /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
234 pub fn eval_bits(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>) -> u128 {
235 self.try_eval_bits(tcx, param_env, ty)
236 .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", ty, self))
240 /// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
241 pub fn eval_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
242 self.try_eval_usize(tcx, param_env)
243 .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
246 pub fn is_ct_infer(self) -> bool {
247 matches!(self.kind(), ty::ConstKind::Infer(_))
251 pub fn const_param_default<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Const<'tcx> {
252 let default_def_id = match tcx.hir().get_by_def_id(def_id.expect_local()) {
253 hir::Node::GenericParam(hir::GenericParam {
254 kind: hir::GenericParamKind::Const { default: Some(ac), .. },
258 tcx.def_span(def_id),
259 "`const_param_default` expected a generic parameter with a constant"
262 Const::from_anon_const(tcx, default_def_id)