1 // Not in interpret to make sure we do not use private implementation details
5 use std::borrow::{Borrow, Cow};
7 use std::collections::hash_map::Entry;
9 use rustc::hir::{self, def_id::DefId};
10 use rustc::hir::def::Def;
11 use rustc::mir::interpret::{ConstEvalErr, ErrorHandled};
13 use rustc::ty::{self, TyCtxt, Instance, query::TyCtxtAt};
14 use rustc::ty::layout::{self, LayoutOf, TyLayout, VariantIdx};
15 use rustc::ty::subst::Subst;
16 use rustc::traits::Reveal;
17 use rustc_data_structures::indexed_vec::IndexVec;
18 use rustc_data_structures::fx::FxHashMap;
19 use rustc::util::common::ErrorReported;
21 use syntax::ast::Mutability;
22 use syntax::source_map::{Span, DUMMY_SP};
24 use crate::interpret::{self,
25 PlaceTy, MPlaceTy, MemPlace, OpTy, Operand, Immediate, Scalar, RawConst, ConstValue, Pointer,
26 EvalResult, EvalError, EvalErrorKind, GlobalId, EvalContext, StackPopCleanup,
27 Allocation, AllocId, MemoryKind,
28 snapshot, RefTracking,
31 /// Number of steps until the detector even starts doing anything.
32 /// Also, a warning is shown to the user when this number is reached.
33 const STEPS_UNTIL_DETECTOR_ENABLED: isize = 1_000_000;
34 /// The number of steps between loop detector snapshots.
35 /// Should be a power of two for performance reasons.
36 const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
38 /// Warning: do not use this function if you expect to start interpreting the given `Mir`.
39 /// The `EvalContext` is only meant to be used to query values from constants and statics.
41 /// This function is used during const propagation. We cannot use `mk_eval_cx`, because copy
42 /// propagation happens *during* the computation of the MIR of the current function. So if we
43 /// tried to call the `optimized_mir` query, we'd get a cycle error because we are (transitively)
44 /// inside the `optimized_mir` query of the `Instance` given.
46 /// Since we are looking at the MIR of the function in an abstract manner, we don't have a
47 /// `ParamEnv` available to us. This function creates a `ParamEnv` for the given instance.
48 pub fn mk_borrowck_eval_cx<'a, 'mir, 'tcx>(
49 tcx: TyCtxt<'a, 'tcx, 'tcx>,
50 instance: Instance<'tcx>,
51 mir: &'mir mir::Mir<'tcx>,
53 ) -> EvalResult<'tcx, CompileTimeEvalContext<'a, 'mir, 'tcx>> {
54 debug!("mk_borrowck_eval_cx: {:?}", instance);
55 let param_env = tcx.param_env(instance.def_id());
56 mk_eval_cx_inner(tcx, instance, mir, span, param_env)
59 /// This is just a helper function to reduce code duplication between `mk_borrowck_eval_cx` and
60 /// `mk_eval_cx`. Do not call this function directly.
61 fn mk_eval_cx_inner<'a, 'mir, 'tcx>(
62 tcx: TyCtxt<'a, 'tcx, 'tcx>,
63 instance: Instance<'tcx>,
64 mir: &'mir mir::Mir<'tcx>,
66 param_env: ty::ParamEnv<'tcx>,
67 ) -> EvalResult<'tcx, CompileTimeEvalContext<'a, 'mir, 'tcx>> {
68 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
69 // Insert a stack frame so any queries have the correct substs.
70 // We also avoid all the extra work performed by push_stack_frame,
71 // like initializing local variables
72 ecx.stack.push(interpret::Frame {
73 block: mir::START_BLOCK,
74 locals: IndexVec::new(),
79 return_to_block: StackPopCleanup::Goto(None), // never pop
86 /// Warning: do not use this function if you expect to start interpreting the given `Mir`.
87 /// The `EvalContext` is only meant to be used to do field and index projections into constants for
88 /// `simd_shuffle` and const patterns in match arms.
90 /// The function containing the `match` that is currently being analyzed may have generic bounds
91 /// that inform us about the generic bounds of the constant. E.g. using an associated constant
92 /// of a function's generic parameter will require knowledge about the bounds on the generic
93 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
94 fn mk_eval_cx<'a, 'tcx>(
95 tcx: TyCtxt<'a, 'tcx, 'tcx>,
96 instance: Instance<'tcx>,
97 param_env: ty::ParamEnv<'tcx>,
98 ) -> EvalResult<'tcx, CompileTimeEvalContext<'a, 'tcx, 'tcx>> {
99 debug!("mk_eval_cx: {:?}, {:?}", instance, param_env);
100 let span = tcx.def_span(instance.def_id());
101 let mir = tcx.optimized_mir(instance.def.def_id());
102 mk_eval_cx_inner(tcx, instance, mir, span, param_env)
105 pub(crate) fn eval_promoted<'a, 'mir, 'tcx>(
106 tcx: TyCtxt<'a, 'tcx, 'tcx>,
108 mir: &'mir mir::Mir<'tcx>,
109 param_env: ty::ParamEnv<'tcx>,
110 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
111 let mut ecx = mk_borrowck_eval_cx(tcx, cid.instance, mir, DUMMY_SP).unwrap();
112 eval_body_using_ecx(&mut ecx, cid, Some(mir), param_env)
115 // FIXME: These two conversion functions are bad hacks. We should just always use allocations.
116 pub fn op_to_const<'tcx>(
117 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
120 ) -> EvalResult<'tcx, ty::Const<'tcx>> {
121 // We do not normalize just any data. Only scalar layout and fat pointers.
122 let normalize = may_normalize
123 && match op.layout.abi {
124 layout::Abi::Scalar(..) => true,
125 layout::Abi::ScalarPair(..) => {
126 // Must be a fat pointer
127 op.layout.ty.builtin_deref(true).is_some()
131 let normalized_op = if normalize {
132 ecx.try_read_immediate(op)?
135 Operand::Indirect(mplace) => Err(mplace),
136 Operand::Immediate(val) => Ok(val)
139 let val = match normalized_op {
140 Err(MemPlace { ptr, align, meta }) => {
141 // extract alloc-offset pair
142 assert!(meta.is_none());
143 let ptr = ptr.to_ptr()?;
144 let alloc = ecx.memory.get(ptr.alloc_id)?;
145 assert!(alloc.align >= align);
146 assert!(alloc.bytes.len() as u64 - ptr.offset.bytes() >= op.layout.size.bytes());
147 let mut alloc = alloc.clone();
149 // FIXME shouldn't it be the case that `mark_static_initialized` has already
150 // interned this? I thought that is the entire point of that `FinishStatic` stuff?
151 let alloc = ecx.tcx.intern_const_alloc(alloc);
152 ConstValue::ByRef(ptr.alloc_id, alloc, ptr.offset)
154 Ok(Immediate::Scalar(x)) =>
155 ConstValue::Scalar(x.not_undef()?),
156 Ok(Immediate::ScalarPair(a, b)) =>
157 ConstValue::ScalarPair(a.not_undef()?, b.not_undef()?),
159 Ok(ty::Const { val, ty: op.layout.ty })
162 pub fn lazy_const_to_op<'tcx>(
163 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
164 cnst: ty::LazyConst<'tcx>,
166 ) -> EvalResult<'tcx, OpTy<'tcx>> {
167 let op = ecx.const_value_to_op(cnst)?;
168 Ok(OpTy { op, layout: ecx.layout_of(ty)? })
171 fn eval_body_and_ecx<'a, 'mir, 'tcx>(
172 tcx: TyCtxt<'a, 'tcx, 'tcx>,
174 mir: Option<&'mir mir::Mir<'tcx>>,
175 param_env: ty::ParamEnv<'tcx>,
176 ) -> (EvalResult<'tcx, MPlaceTy<'tcx>>, CompileTimeEvalContext<'a, 'mir, 'tcx>) {
177 // we start out with the best span we have
178 // and try improving it down the road when more information is available
179 let span = tcx.def_span(cid.instance.def_id());
180 let span = mir.map(|mir| mir.span).unwrap_or(span);
181 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
182 let r = eval_body_using_ecx(&mut ecx, cid, mir, param_env);
186 // Returns a pointer to where the result lives
187 fn eval_body_using_ecx<'mir, 'tcx>(
188 ecx: &mut CompileTimeEvalContext<'_, 'mir, 'tcx>,
190 mir: Option<&'mir mir::Mir<'tcx>>,
191 param_env: ty::ParamEnv<'tcx>,
192 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
193 debug!("eval_body_using_ecx: {:?}, {:?}", cid, param_env);
194 let tcx = ecx.tcx.tcx;
195 let mut mir = match mir {
197 None => ecx.load_mir(cid.instance.def)?,
199 if let Some(index) = cid.promoted {
200 mir = &mir.promoted[index];
202 let layout = ecx.layout_of(mir.return_ty().subst(tcx, cid.instance.substs))?;
203 assert!(!layout.is_unsized());
204 let ret = ecx.allocate(layout, MemoryKind::Stack);
206 let name = ty::tls::with(|tcx| tcx.item_path_str(cid.instance.def_id()));
207 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
208 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
209 assert!(mir.arg_count == 0);
210 ecx.push_stack_frame(
215 StackPopCleanup::None { cleanup: false },
218 // The main interpreter loop.
222 let internally_mutable = !layout.ty.is_freeze(tcx, param_env, mir.span);
223 let is_static = tcx.is_static(cid.instance.def_id());
224 let mutability = if is_static == Some(hir::Mutability::MutMutable) || internally_mutable {
227 Mutability::Immutable
229 ecx.memory.intern_static(ret.ptr.to_ptr()?.alloc_id, mutability)?;
231 debug!("eval_body_using_ecx done: {:?}", *ret);
235 impl<'tcx> Into<EvalError<'tcx>> for ConstEvalError {
236 fn into(self) -> EvalError<'tcx> {
237 EvalErrorKind::MachineError(self.to_string()).into()
241 #[derive(Clone, Debug)]
242 enum ConstEvalError {
246 impl fmt::Display for ConstEvalError {
247 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
248 use self::ConstEvalError::*;
250 NeedsRfc(ref msg) => {
253 "\"{}\" needs an rfc before being allowed inside constants",
261 impl Error for ConstEvalError {
262 fn description(&self) -> &str {
263 use self::ConstEvalError::*;
265 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
269 fn cause(&self) -> Option<&dyn Error> {
274 // Extra machine state for CTFE, and the Machine instance
275 pub struct CompileTimeInterpreter<'a, 'mir, 'tcx: 'a+'mir> {
276 /// When this value is negative, it indicates the number of interpreter
277 /// steps *until* the loop detector is enabled. When it is positive, it is
278 /// the number of steps after the detector has been enabled modulo the loop
280 pub(super) steps_since_detector_enabled: isize,
282 /// Extra state to detect loops.
283 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'a, 'mir, 'tcx>,
286 impl<'a, 'mir, 'tcx> CompileTimeInterpreter<'a, 'mir, 'tcx> {
288 CompileTimeInterpreter {
289 loop_detector: Default::default(),
290 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
295 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
297 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
300 FxHashMap::contains_key(self, k)
304 fn insert(&mut self, k: K, v: V) -> Option<V>
306 FxHashMap::insert(self, k, v)
310 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
313 FxHashMap::remove(self, k)
317 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
319 .filter_map(move |(k, v)| f(k, &*v))
327 vacant: impl FnOnce() -> Result<V, E>
334 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
343 vacant: impl FnOnce() -> Result<V, E>
344 ) -> Result<&mut V, E>
346 match self.entry(k) {
347 Entry::Occupied(e) => Ok(e.into_mut()),
348 Entry::Vacant(e) => {
356 type CompileTimeEvalContext<'a, 'mir, 'tcx> =
357 EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>;
359 impl interpret::MayLeak for ! {
361 fn may_leak(self) -> bool {
362 // `self` is uninhabited
367 impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
368 for CompileTimeInterpreter<'a, 'mir, 'tcx>
370 type MemoryKinds = !;
371 type PointerTag = ();
373 type FrameExtra = ();
374 type MemoryExtra = ();
375 type AllocExtra = ();
377 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
379 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
382 fn enforce_validity(_ecx: &EvalContext<'a, 'mir, 'tcx, Self>) -> bool {
383 false // for now, we don't enforce validity
387 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
388 instance: ty::Instance<'tcx>,
390 dest: Option<PlaceTy<'tcx>>,
391 ret: Option<mir::BasicBlock>,
392 ) -> EvalResult<'tcx, Option<&'mir mir::Mir<'tcx>>> {
393 debug!("eval_fn_call: {:?}", instance);
394 // Execution might have wandered off into other crates, so we cannot to a stability-
395 // sensitive check here. But we can at least rule out functions that are not const
397 if !ecx.tcx.is_const_fn_raw(instance.def_id()) {
398 // Some functions we support even if they are non-const -- but avoid testing
399 // that for const fn! We certainly do *not* want to actually call the fn
400 // though, so be sure we return here.
401 return if ecx.hook_fn(instance, args, dest)? {
402 ecx.goto_block(ret)?; // fully evaluated and done
405 err!(MachineError(format!("calling non-const function `{}`", instance)))
408 // This is a const fn. Call it.
409 Ok(Some(match ecx.load_mir(instance.def) {
412 if let EvalErrorKind::NoMirFor(ref path) = err.kind {
414 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
424 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
425 instance: ty::Instance<'tcx>,
428 ) -> EvalResult<'tcx> {
429 if ecx.emulate_intrinsic(instance, args, dest)? {
432 // An intrinsic that we do not support
433 let intrinsic_name = &ecx.tcx.item_name(instance.def_id()).as_str()[..];
435 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
440 _ecx: &EvalContext<'a, 'mir, 'tcx, Self>,
443 _left_layout: TyLayout<'tcx>,
445 _right_layout: TyLayout<'tcx>,
446 ) -> EvalResult<'tcx, (Scalar, bool)> {
448 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
452 fn find_foreign_static(
454 _tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
456 ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
457 err!(ReadForeignStatic)
461 fn adjust_static_allocation<'b>(
462 alloc: &'b Allocation,
464 ) -> Cow<'b, Allocation<Self::PointerTag>> {
465 // We do not use a tag so we can just cheaply forward the reference
470 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
471 _dest: PlaceTy<'tcx>,
472 ) -> EvalResult<'tcx> {
474 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
478 fn before_terminator(ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>) -> EvalResult<'tcx> {
480 let steps = &mut ecx.machine.steps_since_detector_enabled;
487 *steps %= DETECTOR_SNAPSHOT_PERIOD;
493 let span = ecx.frame().span;
494 ecx.machine.loop_detector.observe_and_analyze(
503 fn tag_new_allocation(
504 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
506 _kind: MemoryKind<Self::MemoryKinds>,
513 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
514 ) -> EvalResult<'tcx> {
518 /// Called immediately before a stack frame gets popped
521 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
523 ) -> EvalResult<'tcx> {
528 /// Project to a field of a (variant of a) const
529 pub fn const_field<'a, 'tcx>(
530 tcx: TyCtxt<'a, 'tcx, 'tcx>,
531 param_env: ty::ParamEnv<'tcx>,
532 instance: ty::Instance<'tcx>,
533 variant: Option<VariantIdx>,
535 value: ty::Const<'tcx>,
536 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
537 trace!("const_field: {:?}, {:?}, {:?}", instance, field, value);
538 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
540 // get the operand again
541 let op = lazy_const_to_op(&ecx, ty::LazyConst::Evaluated(value), value.ty)?;
543 let down = match variant {
545 Some(variant) => ecx.operand_downcast(op, variant)?
548 let field = ecx.operand_field(down, field.index() as u64)?;
549 // and finally move back to the const world, always normalizing because
550 // this is not called for statics.
551 op_to_const(&ecx, field, true)
553 result.map_err(|error| {
554 let err = error_to_const_error(&ecx, error);
555 err.report_as_error(ecx.tcx, "could not access field of constant");
556 ErrorHandled::Reported
560 pub fn const_variant_index<'a, 'tcx>(
561 tcx: TyCtxt<'a, 'tcx, 'tcx>,
562 param_env: ty::ParamEnv<'tcx>,
563 instance: ty::Instance<'tcx>,
564 val: ty::Const<'tcx>,
565 ) -> EvalResult<'tcx, VariantIdx> {
566 trace!("const_variant_index: {:?}, {:?}", instance, val);
567 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
568 let op = lazy_const_to_op(&ecx, ty::LazyConst::Evaluated(val), val.ty)?;
569 Ok(ecx.read_discriminant(op)?.1)
572 pub fn error_to_const_error<'a, 'mir, 'tcx>(
573 ecx: &EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>,
574 mut error: EvalError<'tcx>
575 ) -> ConstEvalErr<'tcx> {
576 error.print_backtrace();
577 let stacktrace = ecx.generate_stacktrace(None);
578 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
581 fn validate_and_turn_into_const<'a, 'tcx>(
582 tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
583 constant: RawConst<'tcx>,
584 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
585 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
587 let ecx = mk_eval_cx(tcx, cid.instance, key.param_env).unwrap();
589 let op = ecx.raw_const_to_mplace(constant)?.into();
590 // FIXME: Once the visitor infrastructure landed, change validation to
591 // work directly on `MPlaceTy`.
592 let mut ref_tracking = RefTracking::new(op);
593 while let Some((op, path)) = ref_tracking.todo.pop() {
594 ecx.validate_operand(
597 Some(&mut ref_tracking),
598 /* const_mode */ true,
601 // Now that we validated, turn this into a proper constant
602 let def_id = cid.instance.def.def_id();
603 let normalize = tcx.is_static(def_id).is_none() && cid.promoted.is_none();
604 op_to_const(&ecx, op, normalize)
607 val.map_err(|error| {
608 let err = error_to_const_error(&ecx, error);
609 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
611 diag.note("The rules on what exactly is undefined behavior aren't clear, \
612 so this check might be overzealous. Please open an issue on the rust compiler \
613 repository if you believe it should not be considered undefined behavior",
616 ErrorHandled::Reported
623 pub fn const_eval_provider<'a, 'tcx>(
624 tcx: TyCtxt<'a, 'tcx, 'tcx>,
625 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
626 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
627 // see comment in const_eval_provider for what we're doing here
628 if key.param_env.reveal == Reveal::All {
629 let mut key = key.clone();
630 key.param_env.reveal = Reveal::UserFacing;
631 match tcx.const_eval(key) {
632 // try again with reveal all as requested
633 Err(ErrorHandled::TooGeneric) => {
634 // Promoteds should never be "too generic" when getting evaluated.
635 // They either don't get evaluated, or we are in a monomorphic context
636 assert!(key.value.promoted.is_none());
639 other => return other,
642 tcx.const_eval_raw(key).and_then(|val| {
643 validate_and_turn_into_const(tcx, val, key)
647 pub fn const_eval_raw_provider<'a, 'tcx>(
648 tcx: TyCtxt<'a, 'tcx, 'tcx>,
649 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
650 ) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
651 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
652 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
653 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
654 // computed. For a large percentage of constants that will already have succeeded. Only
655 // associated constants of generic functions will fail due to not enough monomorphization
656 // information being available.
658 // In case we fail in the `UserFacing` variant, we just do the real computation.
659 if key.param_env.reveal == Reveal::All {
660 let mut key = key.clone();
661 key.param_env.reveal = Reveal::UserFacing;
662 match tcx.const_eval_raw(key) {
663 // try again with reveal all as requested
664 Err(ErrorHandled::TooGeneric) => {},
666 other => return other,
669 // the first trace is for replicating an ice
670 // There's no tracking issue, but the next two lines concatenated link to the discussion on
671 // zulip. It's not really possible to test this, because it doesn't show up in diagnostics
673 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
674 // subject/anon_const_instance_printing/near/135980032
675 trace!("const eval: {}", key.value.instance);
676 trace!("const eval: {:?}", key);
679 let def_id = cid.instance.def.def_id();
681 if let Some(id) = tcx.hir().as_local_node_id(def_id) {
682 let tables = tcx.typeck_tables_of(def_id);
684 // Do match-check before building MIR
685 if let Err(ErrorReported) = tcx.check_match(def_id) {
686 return Err(ErrorHandled::Reported)
689 if let hir::BodyOwnerKind::Const = tcx.hir().body_owner_kind(id) {
690 tcx.mir_const_qualif(def_id);
693 // Do not continue into miri if typeck errors occurred; it will fail horribly
694 if tables.tainted_by_errors {
695 return Err(ErrorHandled::Reported)
699 let (res, ecx) = eval_body_and_ecx(tcx, cid, None, key.param_env);
700 res.and_then(|place| {
702 alloc_id: place.to_ptr().expect("we allocated this ptr!").alloc_id,
706 let err = error_to_const_error(&ecx, error);
707 // errors in statics are always emitted as fatal errors
708 if tcx.is_static(def_id).is_some() {
709 let reported_err = err.report_as_error(ecx.tcx,
710 "could not evaluate static initializer");
711 // Ensure that if the above error was either `TooGeneric` or `Reported`
712 // an error must be reported.
713 if tcx.sess.err_count() == 0 {
714 tcx.sess.delay_span_bug(err.span,
715 &format!("static eval failure did not emit an error: {:#?}",
719 } else if def_id.is_local() {
720 // constant defined in this crate, we can figure out a lint level!
721 match tcx.describe_def(def_id) {
722 // constants never produce a hard error at the definition site. Anything else is
723 // a backwards compatibility hazard (and will break old versions of winapi for sure)
725 // note that validation may still cause a hard error on this very same constant,
726 // because any code that existed before validation could not have failed validation
727 // thus preventing such a hard error from being a backwards compatibility hazard
728 Some(Def::Const(_)) | Some(Def::AssociatedConst(_)) => {
729 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
731 tcx.at(tcx.def_span(def_id)),
732 "any use of this value will cause an error",
736 // promoting runtime code is only allowed to error if it references broken constants
737 // any other kind of error will be reported to the user as a deny-by-default lint
738 _ => if let Some(p) = cid.promoted {
739 let span = tcx.optimized_mir(def_id).promoted[p].span;
740 if let EvalErrorKind::ReferencedConstant = err.error {
743 "evaluation of constant expression failed",
748 "reaching this expression at runtime will panic or abort",
749 tcx.hir().as_local_node_id(def_id).unwrap(),
752 // anything else (array lengths, enum initializers, constant patterns) are reported
757 "evaluation of constant value failed",
762 // use of broken constant from other crate
763 err.report_as_error(ecx.tcx, "could not evaluate constant")