1 use crate::mir::interpret::LitToConstInput;
2 use crate::mir::ConstantKind;
3 use crate::ty::{self, InternalSubsts, ParamEnv, ParamEnvAnd, Ty, TyCtxt};
4 use rustc_data_structures::intern::Interned;
5 use rustc_errors::ErrorGuaranteed;
7 use rustc_hir::def_id::{DefId, LocalDefId};
8 use rustc_macros::HashStable;
19 /// Use this rather than `ConstS`, whenever possible.
20 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, HashStable)]
21 #[rustc_pass_by_value]
22 pub struct Const<'tcx>(pub Interned<'tcx, ConstS<'tcx>>);
24 impl<'tcx> fmt::Debug for Const<'tcx> {
25 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
26 // This reflects what `Const` looked liked before `Interned` was
27 // introduced. We print it like this to avoid having to update expected
28 // output in a lot of tests.
29 write!(f, "Const {{ ty: {:?}, kind: {:?} }}", self.ty(), self.kind())
33 /// Typed constant value.
34 #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, HashStable, TyEncodable, TyDecodable)]
35 pub struct ConstS<'tcx> {
37 pub kind: ConstKind<'tcx>,
40 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
41 static_assert_size!(ConstS<'_>, 40);
43 impl<'tcx> Const<'tcx> {
45 pub fn ty(self) -> Ty<'tcx> {
50 pub fn kind(self) -> ConstKind<'tcx> {
54 /// Literals and const generic parameters are eagerly converted to a constant, everything else
55 /// becomes `Unevaluated`.
56 pub fn from_anon_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
57 Self::from_opt_const_arg_anon_const(tcx, ty::WithOptConstParam::unknown(def_id))
60 #[instrument(skip(tcx), level = "debug")]
61 pub fn from_opt_const_arg_anon_const(
63 def: ty::WithOptConstParam<LocalDefId>,
65 let body_id = match tcx.hir().get_by_def_id(def.did) {
66 hir::Node::AnonConst(ac) => ac.body,
68 tcx.def_span(def.did.to_def_id()),
69 "from_anon_const can only process anonymous constants"
73 let expr = &tcx.hir().body(body_id).value;
76 let ty = tcx.type_of(def.def_id_for_type_of());
78 match Self::try_eval_lit_or_param(tcx, ty, expr) {
80 None => tcx.mk_const(ty::ConstS {
81 kind: ty::ConstKind::Unevaluated(ty::UnevaluatedConst {
83 substs: InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
90 #[instrument(skip(tcx), level = "debug")]
91 fn try_eval_lit_or_param(
94 expr: &'tcx hir::Expr<'tcx>,
96 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
97 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
98 let expr = match &expr.kind {
99 hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
100 block.expr.as_ref().unwrap()
105 let lit_input = match expr.kind {
106 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
107 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => match expr.kind {
108 hir::ExprKind::Lit(ref lit) => {
109 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
116 if let Some(lit_input) = lit_input {
117 // If an error occurred, ignore that it's a literal and leave reporting the error up to
119 match tcx.at(expr.span).lit_to_const(lit_input) {
120 Ok(c) => return Some(c),
122 tcx.sess.delay_span_bug(
124 &format!("Const::from_anon_const: couldn't lit_to_const {:?}", e),
130 use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
132 ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
133 // Find the name and index of the const parameter by indexing the generics of
134 // the parent item and construct a `ParamConst`.
135 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
136 let item_id = tcx.hir().get_parent_node(hir_id);
137 let item_def_id = tcx.hir().local_def_id(item_id);
138 let generics = tcx.generics_of(item_def_id.to_def_id());
139 let index = generics.param_def_id_to_index[&def_id];
140 let name = tcx.hir().name(hir_id);
141 Some(tcx.mk_const(ty::ConstS {
142 kind: ty::ConstKind::Param(ty::ParamConst::new(index, name)),
150 /// Interns the given value as a constant.
152 pub fn from_value(tcx: TyCtxt<'tcx>, val: ty::ValTree<'tcx>, ty: Ty<'tcx>) -> Self {
153 tcx.mk_const(ConstS { kind: ConstKind::Value(val), ty })
156 /// Panics if self.kind != ty::ConstKind::Value
157 pub fn to_valtree(self) -> ty::ValTree<'tcx> {
159 ty::ConstKind::Value(valtree) => valtree,
160 _ => bug!("expected ConstKind::Value, got {:?}", self.kind()),
164 pub fn from_scalar_int(tcx: TyCtxt<'tcx>, i: ScalarInt, ty: Ty<'tcx>) -> Self {
165 let valtree = ty::ValTree::from_scalar_int(i);
166 Self::from_value(tcx, valtree, ty)
170 /// Creates a constant with the given integer value and interns it.
171 pub fn from_bits(tcx: TyCtxt<'tcx>, bits: u128, ty: ParamEnvAnd<'tcx, Ty<'tcx>>) -> Self {
174 .unwrap_or_else(|e| panic!("could not compute layout for {:?}: {:?}", ty, e))
176 Self::from_scalar_int(tcx, ScalarInt::try_from_uint(bits, size).unwrap(), ty.value)
180 /// Creates an interned zst constant.
181 pub fn zero_sized(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
182 let valtree = ty::ValTree::zst();
183 Self::from_value(tcx, valtree, ty)
187 /// Creates an interned bool constant.
188 pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> Self {
189 Self::from_bits(tcx, v as u128, ParamEnv::empty().and(tcx.types.bool))
193 /// Creates an interned usize constant.
194 pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> Self {
195 Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
199 /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
200 /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
201 /// contains const generic parameters or pointers).
202 pub fn try_eval_bits(
205 param_env: ParamEnv<'tcx>,
208 assert_eq!(self.ty(), ty);
209 let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;
210 // if `ty` does not depend on generic parameters, use an empty param_env
211 self.kind().eval(tcx, param_env).try_to_bits(size)
215 pub fn try_eval_bool(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
216 self.kind().eval(tcx, param_env).try_to_bool()
220 pub fn try_eval_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<u64> {
221 self.kind().eval(tcx, param_env).try_to_machine_usize(tcx)
225 /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the
226 /// unevaluated constant.
227 pub fn eval(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Const<'tcx> {
228 if let Some(val) = self.kind().try_eval_for_typeck(tcx, param_env) {
230 Ok(val) => Const::from_value(tcx, val, self.ty()),
231 Err(ErrorGuaranteed { .. }) => tcx.const_error(self.ty()),
234 // Either the constant isn't evaluatable or ValTree creation failed.
240 /// Tries to evaluate the constant if it is `Unevaluated` and creates a ConstValue if the
241 /// evaluation succeeds. If it doesn't succeed, returns the unevaluated constant.
242 pub fn eval_for_mir(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> ConstantKind<'tcx> {
243 if let Some(val) = self.kind().try_eval_for_mir(tcx, param_env) {
245 Ok(const_val) => ConstantKind::from_value(const_val, self.ty()),
246 Err(ErrorGuaranteed { .. }) => ConstantKind::Ty(tcx.const_error(self.ty())),
249 ConstantKind::Ty(self)
254 /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
255 pub fn eval_bits(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>) -> u128 {
256 self.try_eval_bits(tcx, param_env, ty)
257 .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", ty, self))
261 /// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
262 pub fn eval_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
263 self.try_eval_usize(tcx, param_env)
264 .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
268 pub fn const_param_default<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Const<'tcx> {
269 let default_def_id = match tcx.hir().get_by_def_id(def_id.expect_local()) {
270 hir::Node::GenericParam(hir::GenericParam {
271 kind: hir::GenericParamKind::Const { ty: _, default: Some(ac) },
273 }) => tcx.hir().local_def_id(ac.hir_id),
275 tcx.def_span(def_id),
276 "`const_param_default` expected a generic parameter with a constant"
279 Const::from_anon_const(tcx, default_def_id)