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
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, &'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::from_const_value(ecx.tcx.tcx, val, op.layout.ty))
161 pub fn const_to_op<'tcx>(
162 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
163 cnst: &ty::Const<'tcx>,
164 ) -> EvalResult<'tcx, OpTy<'tcx>> {
165 let op = ecx.const_value_to_op(cnst.val)?;
166 Ok(OpTy { op, layout: ecx.layout_of(cnst.ty)? })
169 fn eval_body_and_ecx<'a, 'mir, 'tcx>(
170 tcx: TyCtxt<'a, 'tcx, 'tcx>,
172 mir: Option<&'mir mir::Mir<'tcx>>,
173 param_env: ty::ParamEnv<'tcx>,
174 ) -> (EvalResult<'tcx, MPlaceTy<'tcx>>, CompileTimeEvalContext<'a, 'mir, 'tcx>) {
175 // we start out with the best span we have
176 // and try improving it down the road when more information is available
177 let span = tcx.def_span(cid.instance.def_id());
178 let span = mir.map(|mir| mir.span).unwrap_or(span);
179 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
180 let r = eval_body_using_ecx(&mut ecx, cid, mir, param_env);
184 // Returns a pointer to where the result lives
185 fn eval_body_using_ecx<'mir, 'tcx>(
186 ecx: &mut CompileTimeEvalContext<'_, 'mir, 'tcx>,
188 mir: Option<&'mir mir::Mir<'tcx>>,
189 param_env: ty::ParamEnv<'tcx>,
190 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
191 debug!("eval_body_using_ecx: {:?}, {:?}", cid, param_env);
192 let tcx = ecx.tcx.tcx;
193 let mut mir = match mir {
195 None => ecx.load_mir(cid.instance.def)?,
197 if let Some(index) = cid.promoted {
198 mir = &mir.promoted[index];
200 let layout = ecx.layout_of(mir.return_ty().subst(tcx, cid.instance.substs))?;
201 assert!(!layout.is_unsized());
202 let ret = ecx.allocate(layout, MemoryKind::Stack);
204 let name = ty::tls::with(|tcx| tcx.item_path_str(cid.instance.def_id()));
205 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
206 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
207 assert!(mir.arg_count == 0);
208 ecx.push_stack_frame(
213 StackPopCleanup::None { cleanup: false },
216 // The main interpreter loop.
220 let internally_mutable = !layout.ty.is_freeze(tcx, param_env, mir.span);
221 let is_static = tcx.is_static(cid.instance.def_id());
222 let mutability = if is_static == Some(hir::Mutability::MutMutable) || internally_mutable {
225 Mutability::Immutable
227 ecx.memory.intern_static(ret.ptr.to_ptr()?.alloc_id, mutability)?;
229 debug!("eval_body_using_ecx done: {:?}", *ret);
233 impl<'tcx> Into<EvalError<'tcx>> for ConstEvalError {
234 fn into(self) -> EvalError<'tcx> {
235 EvalErrorKind::MachineError(self.to_string()).into()
239 #[derive(Clone, Debug)]
240 enum ConstEvalError {
244 impl fmt::Display for ConstEvalError {
245 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
246 use self::ConstEvalError::*;
248 NeedsRfc(ref msg) => {
251 "\"{}\" needs an rfc before being allowed inside constants",
259 impl Error for ConstEvalError {
260 fn description(&self) -> &str {
261 use self::ConstEvalError::*;
263 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
267 fn cause(&self) -> Option<&dyn Error> {
272 // Extra machine state for CTFE, and the Machine instance
273 pub struct CompileTimeInterpreter<'a, 'mir, 'tcx: 'a+'mir> {
274 /// When this value is negative, it indicates the number of interpreter
275 /// steps *until* the loop detector is enabled. When it is positive, it is
276 /// the number of steps after the detector has been enabled modulo the loop
278 pub(super) steps_since_detector_enabled: isize,
280 /// Extra state to detect loops.
281 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'a, 'mir, 'tcx>,
284 impl<'a, 'mir, 'tcx> CompileTimeInterpreter<'a, 'mir, 'tcx> {
286 CompileTimeInterpreter {
287 loop_detector: Default::default(),
288 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
293 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
295 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
298 FxHashMap::contains_key(self, k)
302 fn insert(&mut self, k: K, v: V) -> Option<V>
304 FxHashMap::insert(self, k, v)
308 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
311 FxHashMap::remove(self, k)
315 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
317 .filter_map(move |(k, v)| f(k, &*v))
325 vacant: impl FnOnce() -> Result<V, E>
332 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
341 vacant: impl FnOnce() -> Result<V, E>
342 ) -> Result<&mut V, E>
344 match self.entry(k) {
345 Entry::Occupied(e) => Ok(e.into_mut()),
346 Entry::Vacant(e) => {
354 type CompileTimeEvalContext<'a, 'mir, 'tcx> =
355 EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>;
357 impl interpret::MayLeak for ! {
359 fn may_leak(self) -> bool {
360 // `self` is uninhabited
365 impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
366 for CompileTimeInterpreter<'a, 'mir, 'tcx>
368 type MemoryKinds = !;
369 type PointerTag = ();
371 type FrameExtra = ();
372 type MemoryExtra = ();
373 type AllocExtra = ();
375 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
377 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
380 fn enforce_validity(_ecx: &EvalContext<'a, 'mir, 'tcx, Self>) -> bool {
381 false // for now, we don't enforce validity
385 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
386 instance: ty::Instance<'tcx>,
388 dest: Option<PlaceTy<'tcx>>,
389 ret: Option<mir::BasicBlock>,
390 ) -> EvalResult<'tcx, Option<&'mir mir::Mir<'tcx>>> {
391 debug!("eval_fn_call: {:?}", instance);
392 // Execution might have wandered off into other crates, so we cannot to a stability-
393 // sensitive check here. But we can at least rule out functions that are not const
395 if !ecx.tcx.is_const_fn_raw(instance.def_id()) {
396 // Some functions we support even if they are non-const -- but avoid testing
397 // that for const fn! We certainly do *not* want to actually call the fn
398 // though, so be sure we return here.
399 return if ecx.hook_fn(instance, args, dest)? {
400 ecx.goto_block(ret)?; // fully evaluated and done
403 err!(MachineError(format!("calling non-const function `{}`", instance)))
406 // This is a const fn. Call it.
407 Ok(Some(match ecx.load_mir(instance.def) {
410 if let EvalErrorKind::NoMirFor(ref path) = err.kind {
412 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
422 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
423 instance: ty::Instance<'tcx>,
426 ) -> EvalResult<'tcx> {
427 if ecx.emulate_intrinsic(instance, args, dest)? {
430 // An intrinsic that we do not support
431 let intrinsic_name = &ecx.tcx.item_name(instance.def_id()).as_str()[..];
433 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
438 _ecx: &EvalContext<'a, 'mir, 'tcx, Self>,
441 _left_layout: TyLayout<'tcx>,
443 _right_layout: TyLayout<'tcx>,
444 ) -> EvalResult<'tcx, (Scalar, bool)> {
446 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
450 fn find_foreign_static(
452 _tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
454 ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
455 err!(ReadForeignStatic)
459 fn adjust_static_allocation<'b>(
460 alloc: &'b Allocation,
462 ) -> Cow<'b, Allocation<Self::PointerTag>> {
463 // We do not use a tag so we can just cheaply forward the reference
468 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
469 _dest: PlaceTy<'tcx>,
470 ) -> EvalResult<'tcx> {
472 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
476 fn before_terminator(ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>) -> EvalResult<'tcx> {
478 let steps = &mut ecx.machine.steps_since_detector_enabled;
485 *steps %= DETECTOR_SNAPSHOT_PERIOD;
491 let span = ecx.frame().span;
492 ecx.machine.loop_detector.observe_and_analyze(
501 fn tag_new_allocation(
502 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
504 _kind: MemoryKind<Self::MemoryKinds>,
511 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
512 ) -> EvalResult<'tcx> {
516 /// Called immediately before a stack frame gets popped
519 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
521 ) -> EvalResult<'tcx> {
526 /// Project to a field of a (variant of a) const
527 pub fn const_field<'a, 'tcx>(
528 tcx: TyCtxt<'a, 'tcx, 'tcx>,
529 param_env: ty::ParamEnv<'tcx>,
530 instance: ty::Instance<'tcx>,
531 variant: Option<VariantIdx>,
533 value: &'tcx ty::Const<'tcx>,
534 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
535 trace!("const_field: {:?}, {:?}, {:?}", instance, field, value);
536 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
538 // get the operand again
539 let op = const_to_op(&ecx, value)?;
541 let down = match variant {
543 Some(variant) => ecx.operand_downcast(op, variant)?
546 let field = ecx.operand_field(down, field.index() as u64)?;
547 // and finally move back to the const world, always normalizing because
548 // this is not called for statics.
549 op_to_const(&ecx, field, true)
551 result.map_err(|error| {
552 let err = error_to_const_error(&ecx, error);
553 err.report_as_error(ecx.tcx, "could not access field of constant");
554 ErrorHandled::Reported
558 pub fn const_variant_index<'a, 'tcx>(
559 tcx: TyCtxt<'a, 'tcx, 'tcx>,
560 param_env: ty::ParamEnv<'tcx>,
561 instance: ty::Instance<'tcx>,
562 val: &'tcx ty::Const<'tcx>,
563 ) -> EvalResult<'tcx, VariantIdx> {
564 trace!("const_variant_index: {:?}, {:?}", instance, val);
565 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
566 let op = const_to_op(&ecx, val)?;
567 Ok(ecx.read_discriminant(op)?.1)
570 pub fn error_to_const_error<'a, 'mir, 'tcx>(
571 ecx: &EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>,
572 mut error: EvalError<'tcx>
573 ) -> ConstEvalErr<'tcx> {
574 error.print_backtrace();
575 let stacktrace = ecx.generate_stacktrace(None);
576 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
579 fn validate_and_turn_into_const<'a, 'tcx>(
580 tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
581 constant: RawConst<'tcx>,
582 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
583 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
585 let ecx = mk_eval_cx(tcx, cid.instance, key.param_env).unwrap();
587 let op = ecx.raw_const_to_mplace(constant)?.into();
588 // FIXME: Once the visitor infrastructure landed, change validation to
589 // work directly on `MPlaceTy`.
590 let mut ref_tracking = RefTracking::new(op);
591 while let Some((op, path)) = ref_tracking.todo.pop() {
592 ecx.validate_operand(
595 Some(&mut ref_tracking),
596 /* const_mode */ true,
599 // Now that we validated, turn this into a proper constant
600 let def_id = cid.instance.def.def_id();
601 let normalize = tcx.is_static(def_id).is_none() && cid.promoted.is_none();
602 op_to_const(&ecx, op, normalize)
605 val.map_err(|error| {
606 let err = error_to_const_error(&ecx, error);
607 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
609 diag.note("The rules on what exactly is undefined behavior aren't clear, \
610 so this check might be overzealous. Please open an issue on the rust compiler \
611 repository if you believe it should not be considered undefined behavior",
614 ErrorHandled::Reported
621 pub fn const_eval_provider<'a, 'tcx>(
622 tcx: TyCtxt<'a, 'tcx, 'tcx>,
623 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
624 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
625 // see comment in const_eval_provider for what we're doing here
626 if key.param_env.reveal == Reveal::All {
627 let mut key = key.clone();
628 key.param_env.reveal = Reveal::UserFacing;
629 match tcx.const_eval(key) {
630 // try again with reveal all as requested
631 Err(ErrorHandled::TooGeneric) => {
632 // Promoteds should never be "too generic" when getting evaluated.
633 // They either don't get evaluated, or we are in a monomorphic context
634 assert!(key.value.promoted.is_none());
637 other => return other,
640 tcx.const_eval_raw(key).and_then(|val| {
641 validate_and_turn_into_const(tcx, val, key)
645 pub fn const_eval_raw_provider<'a, 'tcx>(
646 tcx: TyCtxt<'a, 'tcx, 'tcx>,
647 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
648 ) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
649 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
650 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
651 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
652 // computed. For a large percentage of constants that will already have succeeded. Only
653 // associated constants of generic functions will fail due to not enough monomorphization
654 // information being available.
656 // In case we fail in the `UserFacing` variant, we just do the real computation.
657 if key.param_env.reveal == Reveal::All {
658 let mut key = key.clone();
659 key.param_env.reveal = Reveal::UserFacing;
660 match tcx.const_eval_raw(key) {
661 // try again with reveal all as requested
662 Err(ErrorHandled::TooGeneric) => {},
664 other => return other,
667 // the first trace is for replicating an ice
668 // There's no tracking issue, but the next two lines concatenated link to the discussion on
669 // zulip. It's not really possible to test this, because it doesn't show up in diagnostics
671 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
672 // subject/anon_const_instance_printing/near/135980032
673 trace!("const eval: {}", key.value.instance);
674 trace!("const eval: {:?}", key);
677 let def_id = cid.instance.def.def_id();
679 if let Some(id) = tcx.hir().as_local_node_id(def_id) {
680 let tables = tcx.typeck_tables_of(def_id);
682 // Do match-check before building MIR
683 if let Err(ErrorReported) = tcx.check_match(def_id) {
684 return Err(ErrorHandled::Reported)
687 if let hir::BodyOwnerKind::Const = tcx.hir().body_owner_kind(id) {
688 tcx.mir_const_qualif(def_id);
691 // Do not continue into miri if typeck errors occurred; it will fail horribly
692 if tables.tainted_by_errors {
693 return Err(ErrorHandled::Reported)
697 let (res, ecx) = eval_body_and_ecx(tcx, cid, None, key.param_env);
698 res.and_then(|place| {
700 alloc_id: place.to_ptr().expect("we allocated this ptr!").alloc_id,
704 let err = error_to_const_error(&ecx, error);
705 // errors in statics are always emitted as fatal errors
706 if tcx.is_static(def_id).is_some() {
707 let reported_err = err.report_as_error(ecx.tcx,
708 "could not evaluate static initializer");
709 // Ensure that if the above error was either `TooGeneric` or `Reported`
710 // an error must be reported.
711 if tcx.sess.err_count() == 0 {
712 tcx.sess.delay_span_bug(err.span,
713 &format!("static eval failure did not emit an error: {:#?}",
717 } else if def_id.is_local() {
718 // constant defined in this crate, we can figure out a lint level!
719 match tcx.describe_def(def_id) {
720 // constants never produce a hard error at the definition site. Anything else is
721 // a backwards compatibility hazard (and will break old versions of winapi for sure)
723 // note that validation may still cause a hard error on this very same constant,
724 // because any code that existed before validation could not have failed validation
725 // thus preventing such a hard error from being a backwards compatibility hazard
726 Some(Def::Const(_)) | Some(Def::AssociatedConst(_)) => {
727 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
729 tcx.at(tcx.def_span(def_id)),
730 "any use of this value will cause an error",
734 // promoting runtime code is only allowed to error if it references broken constants
735 // any other kind of error will be reported to the user as a deny-by-default lint
736 _ => if let Some(p) = cid.promoted {
737 let span = tcx.optimized_mir(def_id).promoted[p].span;
738 if let EvalErrorKind::ReferencedConstant = err.error {
741 "evaluation of constant expression failed",
746 "reaching this expression at runtime will panic or abort",
747 tcx.hir().as_local_node_id(def_id).unwrap(),
750 // anything else (array lengths, enum initializers, constant patterns) are reported
755 "evaluation of constant value failed",
760 // use of broken constant from other crate
761 err.report_as_error(ecx.tcx, "could not evaluate constant")