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

use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_session::lint;
use rustc_span::{Span, DUMMY_SP};
use tracing::{debug, instrument};

use super::{
    ErrorHandled, EvalToAllocationRawResult, EvalToConstValueResult, EvalToValTreeResult, GlobalId,
};
use crate::mir;
use crate::query::TyCtxtEnsure;
use crate::ty::visit::TypeVisitableExt;
use crate::ty::{self, GenericArgs, TyCtxt};

impl<'tcx> TyCtxt<'tcx> {
    /// Evaluates a constant without providing any generic parameters. This is useful to evaluate consts
    /// that can't take any generic arguments like 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 generic parameters within scope, but they aren't allowed
        // to be used. So we can't use `Instance::mono`, instead we feed unresolved generic parameters
        // 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, DUMMY_SP)
    }

    /// Evaluates a constant without providing any generic parameters. This is useful to evaluate consts
    /// that can't take any generic arguments like 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_to_alloc(self, def_id: DefId) -> EvalToAllocationRawResult<'tcx> {
        // In some situations def_id will have generic parameters within scope, but they aren't allowed
        // to be used. So we can't use `Instance::mono`, instead we feed unresolved generic parameters
        // 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);
        let inputs = self.erase_regions(param_env.and(cid));
        self.eval_to_allocation_raw(inputs)
    }

    /// Resolves and evaluates a constant.
    ///
    /// The constant can be located on a trait like `<A as B>::C`, in which case the given
    /// generic parameters and environment are used to resolve the constant. Alternatively if the
    /// constant has generic parameters in scope the generic parameters 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 instantiation for `T`, if the instantiation 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: 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::try_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: 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::try_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.node_span_lint(
                                lint::builtin::CONST_EVALUATABLE_UNCHECKED,
                                self.local_def_id_to_hir_id(local_def_id),
                                self.def_span(ct.def),
                                |lint| { lint.primary_message("cannot use constants which depend on generic parameters in types"); },
                            )
                        }
                    }
                })
            }
            // 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: 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: 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.with_reveal_all_normalized(self).and(cid));
        if !span.is_dummy() {
            // 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: 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.with_reveal_all_normalized(self).and(cid));
        debug!(?inputs);
        if !span.is_dummy() {
            // 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)
        }
    }
}

impl<'tcx> TyCtxtEnsure<'tcx> {
    /// Evaluates a constant without providing any generic parameters. This is useful to evaluate consts
    /// that can't take any generic arguments like 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 generic parameters within scope, but they aren't allowed
        // to be used. So we can't use `Instance::mono`, instead we feed unresolved generic parameters
        // 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)
    }
}