1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
use crate::middle::resolve_bound_vars as rbv;
use crate::mir::interpret::{ErrorHandled, LitToConstInput, Scalar};
use crate::ty::{self, GenericArgs, ParamEnv, ParamEnvAnd, Ty, TyCtxt, TypeVisitableExt};
use rustc_data_structures::intern::Interned;
use rustc_error_messages::MultiSpan;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::LocalDefId;
use rustc_macros::HashStable;
use rustc_type_ir::ConstKind as IrConstKind;
use rustc_type_ir::{ConstTy, IntoKind, TypeFlags, WithCachedTypeInfo};

mod int;
mod kind;
mod valtree;

pub use int::*;
pub use kind::*;
use rustc_span::Span;
use rustc_span::DUMMY_SP;
pub use valtree::*;

pub type ConstKind<'tcx> = IrConstKind<TyCtxt<'tcx>>;

/// Use this rather than `ConstData`, whenever possible.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, HashStable)]
#[rustc_pass_by_value]
pub struct Const<'tcx>(pub(super) Interned<'tcx, WithCachedTypeInfo<ConstData<'tcx>>>);

impl<'tcx> IntoKind for Const<'tcx> {
    type Kind = ConstKind<'tcx>;

    fn kind(self) -> ConstKind<'tcx> {
        self.kind()
    }
}

impl<'tcx> rustc_type_ir::visit::Flags for Const<'tcx> {
    fn flags(&self) -> TypeFlags {
        self.0.flags
    }

    fn outer_exclusive_binder(&self) -> rustc_type_ir::DebruijnIndex {
        self.0.outer_exclusive_binder
    }
}

impl<'tcx> ConstTy<TyCtxt<'tcx>> for Const<'tcx> {
    fn ty(self) -> Ty<'tcx> {
        self.ty()
    }
}

/// Typed constant value.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[derive(HashStable, TyEncodable, TyDecodable)]
pub struct ConstData<'tcx> {
    pub ty: Ty<'tcx>,
    pub kind: ConstKind<'tcx>,
}

#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
static_assert_size!(ConstData<'_>, 40);

impl<'tcx> Const<'tcx> {
    #[inline]
    pub fn ty(self) -> Ty<'tcx> {
        self.0.ty
    }

    #[inline]
    pub fn kind(self) -> ConstKind<'tcx> {
        self.0.kind
    }

    // FIXME(compiler-errors): Think about removing this.
    #[inline]
    pub fn flags(self) -> TypeFlags {
        self.0.flags
    }

    // FIXME(compiler-errors): Think about removing this.
    #[inline]
    pub fn outer_exclusive_binder(self) -> ty::DebruijnIndex {
        self.0.outer_exclusive_binder
    }

    #[inline]
    pub fn new(tcx: TyCtxt<'tcx>, kind: ty::ConstKind<'tcx>, ty: Ty<'tcx>) -> Const<'tcx> {
        tcx.mk_ct_from_kind(kind, ty)
    }

    #[inline]
    pub fn new_param(tcx: TyCtxt<'tcx>, param: ty::ParamConst, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Param(param), ty)
    }

    #[inline]
    pub fn new_var(tcx: TyCtxt<'tcx>, infer: ty::ConstVid, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Infer(ty::InferConst::Var(infer)), ty)
    }

    #[inline]
    pub fn new_fresh(tcx: TyCtxt<'tcx>, fresh: u32, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Infer(ty::InferConst::Fresh(fresh)), ty)
    }

    #[inline]
    pub fn new_infer(tcx: TyCtxt<'tcx>, infer: ty::InferConst, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Infer(infer), ty)
    }

    #[inline]
    pub fn new_bound(
        tcx: TyCtxt<'tcx>,
        debruijn: ty::DebruijnIndex,
        var: ty::BoundVar,
        ty: Ty<'tcx>,
    ) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Bound(debruijn, var), ty)
    }

    #[inline]
    pub fn new_placeholder(
        tcx: TyCtxt<'tcx>,
        placeholder: ty::PlaceholderConst,
        ty: Ty<'tcx>,
    ) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Placeholder(placeholder), ty)
    }

    #[inline]
    pub fn new_unevaluated(
        tcx: TyCtxt<'tcx>,
        uv: ty::UnevaluatedConst<'tcx>,
        ty: Ty<'tcx>,
    ) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Unevaluated(uv), ty)
    }

    #[inline]
    pub fn new_value(tcx: TyCtxt<'tcx>, val: ty::ValTree<'tcx>, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Value(val), ty)
    }

    #[inline]
    pub fn new_expr(tcx: TyCtxt<'tcx>, expr: ty::Expr<'tcx>, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Expr(expr), ty)
    }

    #[inline]
    pub fn new_error(tcx: TyCtxt<'tcx>, e: ty::ErrorGuaranteed, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new(tcx, ty::ConstKind::Error(e), ty)
    }

    /// Like [Ty::new_error] but for constants.
    #[track_caller]
    pub fn new_misc_error(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Const<'tcx> {
        Const::new_error_with_message(
            tcx,
            ty,
            DUMMY_SP,
            "ty::ConstKind::Error constructed but no error reported",
        )
    }

    /// Like [Ty::new_error_with_message] but for constants.
    #[track_caller]
    pub fn new_error_with_message<S: Into<MultiSpan>>(
        tcx: TyCtxt<'tcx>,
        ty: Ty<'tcx>,
        span: S,
        msg: &'static str,
    ) -> Const<'tcx> {
        let reported = tcx.dcx().span_delayed_bug(span, msg);
        Const::new_error(tcx, reported, ty)
    }
}

impl<'tcx> rustc_type_ir::new::Const<TyCtxt<'tcx>> for Const<'tcx> {
    fn new_anon_bound(
        tcx: TyCtxt<'tcx>,
        debruijn: ty::DebruijnIndex,
        var: ty::BoundVar,
        ty: Ty<'tcx>,
    ) -> Self {
        Const::new_bound(tcx, debruijn, var, ty)
    }
}

impl<'tcx> Const<'tcx> {
    /// 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,
            _ => span_bug!(
                tcx.def_span(def.to_def_id()),
                "from_anon_const can only process anonymous constants"
            ),
        };

        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_or_param(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()),
                },
                ty,
            ),
        }
    }

    #[instrument(skip(tcx), level = "debug")]
    fn try_from_lit_or_param(
        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,
        };

        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(e) => {
                    tcx.dcx().span_delayed_bug(
                        expr.span,
                        format!("Const::from_anon_const: couldn't lit_to_const {e:?}"),
                    );
                }
            }
        }

        // FIXME(const_generics): We currently have to special case parameters because `min_const_generics`
        // does not provide the parents generics to anonymous constants. We still allow generic const
        // parameters by themselves however, e.g. `N`. These constants would cause an ICE if we were to
        // ever try to instantiate the generic parameters in their bodies.
        match expr.kind {
            hir::ExprKind::Path(hir::QPath::Resolved(
                _,
                &hir::Path { res: Res::Def(DefKind::ConstParam, def_id), .. },
            )) => {
                // Use the type from the param's definition, since we can resolve it,
                // not the expected parameter type from WithOptConstParam.
                let param_ty = tcx.type_of(def_id).instantiate_identity();
                match tcx.named_bound_var(expr.hir_id) {
                    Some(rbv::ResolvedArg::EarlyBound(_)) => {
                        // Find the name and index of the const parameter by indexing the generics of
                        // the parent item and construct a `ParamConst`.
                        let item_def_id = tcx.parent(def_id);
                        let generics = tcx.generics_of(item_def_id);
                        let index = generics.param_def_id_to_index[&def_id];
                        let name = tcx.item_name(def_id);
                        Some(ty::Const::new_param(tcx, ty::ParamConst::new(index, name), param_ty))
                    }
                    Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => {
                        Some(ty::Const::new_bound(
                            tcx,
                            debruijn,
                            ty::BoundVar::from_u32(index),
                            param_ty,
                        ))
                    }
                    Some(rbv::ResolvedArg::Error(guar)) => {
                        Some(ty::Const::new_error(tcx, guar, param_ty))
                    }
                    arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", expr.hir_id),
                }
            }
            _ => None,
        }
    }

    #[inline]
    /// Creates a constant with the given integer value and interns it.
    pub fn from_bits(tcx: TyCtxt<'tcx>, bits: u128, ty: ParamEnvAnd<'tcx, Ty<'tcx>>) -> Self {
        let size = tcx
            .layout_of(ty)
            .unwrap_or_else(|e| panic!("could not compute layout for {ty:?}: {e:?}"))
            .size;
        ty::Const::new_value(
            tcx,
            ty::ValTree::from_scalar_int(ScalarInt::try_from_uint(bits, size).unwrap()),
            ty.value,
        )
    }

    #[inline]
    /// Creates an interned zst constant.
    pub fn zero_sized(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
        ty::Const::new_value(tcx, ty::ValTree::zst(), ty)
    }

    #[inline]
    /// Creates an interned bool constant.
    pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> Self {
        Self::from_bits(tcx, v as u128, ParamEnv::empty().and(tcx.types.bool))
    }

    #[inline]
    /// Creates an interned usize constant.
    pub fn from_target_usize(tcx: TyCtxt<'tcx>, n: u64) -> Self {
        Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
    }

    /// Returns the evaluated constant
    #[inline]
    pub fn eval(
        self,
        tcx: TyCtxt<'tcx>,
        param_env: ParamEnv<'tcx>,
        span: Option<Span>,
    ) -> Result<ValTree<'tcx>, ErrorHandled> {
        assert!(!self.has_escaping_bound_vars(), "escaping vars in {self:?}");
        match self.kind() {
            ConstKind::Unevaluated(unevaluated) => {
                // FIXME(eddyb) maybe the `const_eval_*` methods should take
                // `ty::ParamEnvAnd` instead of having them separate.
                let (param_env, unevaluated) = unevaluated.prepare_for_eval(tcx, param_env);
                // try to resolve e.g. associated constants to their definition on an impl, and then
                // evaluate the const.
                let Some(c) = tcx.const_eval_resolve_for_typeck(param_env, unevaluated, span)?
                else {
                    // This can happen when we run on ill-typed code.
                    let e = tcx.dcx().span_delayed_bug(
                        span.unwrap_or(DUMMY_SP),
                        "`ty::Const::eval` called on a non-valtree-compatible type",
                    );
                    return Err(e.into());
                };
                Ok(c)
            }
            ConstKind::Value(val) => Ok(val),
            ConstKind::Error(g) => Err(g.into()),
            ConstKind::Param(_)
            | ConstKind::Infer(_)
            | ConstKind::Bound(_, _)
            | ConstKind::Placeholder(_)
            | ConstKind::Expr(_) => Err(ErrorHandled::TooGeneric(span.unwrap_or(DUMMY_SP))),
        }
    }

    /// Normalizes the constant to a value or an error if possible.
    #[inline]
    pub fn normalize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Self {
        match self.eval(tcx, param_env, None) {
            Ok(val) => Self::new_value(tcx, val, self.ty()),
            Err(ErrorHandled::Reported(r, _span)) => Self::new_error(tcx, r.into(), self.ty()),
            Err(ErrorHandled::TooGeneric(_span)) => self,
        }
    }

    #[inline]
    pub fn try_eval_scalar(
        self,
        tcx: TyCtxt<'tcx>,
        param_env: ty::ParamEnv<'tcx>,
    ) -> Option<Scalar> {
        self.eval(tcx, param_env, None).ok()?.try_to_scalar()
    }

    #[inline]
    /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
    /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
    /// contains const generic parameters or pointers).
    pub fn try_eval_scalar_int(
        self,
        tcx: TyCtxt<'tcx>,
        param_env: ParamEnv<'tcx>,
    ) -> Option<ScalarInt> {
        self.try_eval_scalar(tcx, param_env)?.try_to_int().ok()
    }

    #[inline]
    /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
    /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
    /// contains const generic parameters or pointers).
    pub fn try_eval_bits(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<u128> {
        let int = self.try_eval_scalar_int(tcx, param_env)?;
        let size =
            tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(self.ty())).ok()?.size;
        // if `ty` does not depend on generic parameters, use an empty param_env
        int.to_bits(size).ok()
    }

    #[inline]
    /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
    pub fn eval_bits(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u128 {
        self.try_eval_bits(tcx, param_env)
            .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", self.ty(), self))
    }

    #[inline]
    pub fn try_eval_target_usize(
        self,
        tcx: TyCtxt<'tcx>,
        param_env: ParamEnv<'tcx>,
    ) -> Option<u64> {
        self.try_eval_scalar_int(tcx, param_env)?.try_to_target_usize(tcx).ok()
    }

    #[inline]
    pub fn try_eval_bool(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
        self.try_eval_scalar_int(tcx, param_env)?.try_into().ok()
    }

    #[inline]
    /// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
    pub fn eval_target_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
        self.try_eval_target_usize(tcx, param_env)
            .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
    }

    /// Panics if self.kind != ty::ConstKind::Value
    pub fn to_valtree(self) -> ty::ValTree<'tcx> {
        match self.kind() {
            ty::ConstKind::Value(valtree) => valtree,
            _ => bug!("expected ConstKind::Value, got {:?}", self.kind()),
        }
    }

    /// Attempts to convert to a `ValTree`
    pub fn try_to_valtree(self) -> Option<ty::ValTree<'tcx>> {
        match self.kind() {
            ty::ConstKind::Value(valtree) => Some(valtree),
            _ => None,
        }
    }

    #[inline]
    pub fn try_to_scalar(self) -> Option<Scalar> {
        self.try_to_valtree()?.try_to_scalar()
    }

    #[inline]
    pub fn try_to_target_usize(self, tcx: TyCtxt<'tcx>) -> Option<u64> {
        self.try_to_valtree()?.try_to_target_usize(tcx)
    }

    pub fn is_ct_infer(self) -> bool {
        matches!(self.kind(), ty::ConstKind::Infer(_))
    }
}

pub fn const_param_default(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Const<'_>> {
    let default_def_id = match tcx.hir_node_by_def_id(def_id) {
        hir::Node::GenericParam(hir::GenericParam {
            kind: hir::GenericParamKind::Const { default: Some(ac), .. },
            ..
        }) => ac.def_id,
        _ => span_bug!(
            tcx.def_span(def_id),
            "`const_param_default` expected a generic parameter with a constant"
        ),
    };
    ty::EarlyBinder::bind(Const::from_anon_const(tcx, default_def_id))
}