rustc: evaluate fixed-length array length expressions lazily.

Author: eddyb

src/librustc/ich/impls_ty.rs

@@ -234,6 +234,10 @@ impl<'a, 'gcx, 'tcx> HashStable<StableHashingContext<'a, 'gcx, 'tcx>> for ty::Pr
                 def_id.hash_stable(hcx, hasher);
                 closure_kind.hash_stable(hcx, hasher);
             }
+            ty::Predicate::ConstEvaluatable(def_id, substs) => {
+                def_id.hash_stable(hcx, hasher);
+                substs.hash_stable(hcx, hasher);
+            }
         }
     }
 }
@@ -316,6 +320,10 @@ for ::middle::const_val::ConstVal<'gcx> {
                 value.hash_stable(hcx, hasher);
                 times.hash_stable(hcx, hasher);
             }
+            Unevaluated(def_id, substs) => {
+                def_id.hash_stable(hcx, hasher);
+                substs.hash_stable(hcx, hasher);
+            }
         }
     }
 }

src/librustc/infer/mod.rs

@@ -442,6 +442,7 @@ macro_rules! impl_trans_normalize {
 
 impl_trans_normalize!('gcx,
     Ty<'gcx>,
+    &'gcx ty::Const<'gcx>,
     &'gcx Substs<'gcx>,
     ty::FnSig<'gcx>,
     ty::PolyFnSig<'gcx>,
@@ -493,7 +494,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
         let param_env = ty::ParamEnv::empty(Reveal::All);
         let value = self.erase_regions(value);
 
-        if !value.has_projection_types() {
+        if !value.has_projections() {
             return value;
         }
 
@@ -515,7 +516,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
 
         let value = self.erase_regions(value);
 
-        if !value.has_projection_types() {
+        if !value.has_projections() {
             return value;
         }
 

src/librustc/middle/const_val.rs

@@ -41,6 +41,7 @@ pub enum ConstVal<'tcx> {
     Variant(DefId),
     Function(DefId, &'tcx Substs<'tcx>),
     Aggregate(ConstAggregate<'tcx>),
+    Unevaluated(DefId, &'tcx Substs<'tcx>),
 }
 
 #[derive(Copy, Clone, Debug, Hash, RustcEncodable, Eq, PartialEq)]

src/librustc/middle/free_region.rs

@@ -147,7 +147,8 @@ impl<'tcx> FreeRegionMap<'tcx> {
                 ty::Predicate::WellFormed(..) |
                 ty::Predicate::ObjectSafe(..) |
                 ty::Predicate::ClosureKind(..) |
-                ty::Predicate::TypeOutlives(..) => {
+                ty::Predicate::TypeOutlives(..) |
+                ty::Predicate::ConstEvaluatable(..) => {
                     // No region bounds here
                 }
                 ty::Predicate::RegionOutlives(ty::Binder(ty::OutlivesPredicate(r_a, r_b))) => {

src/librustc/middle/mem_categorization.rs

@@ -879,7 +879,8 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
 
         // Always promote `[T; 0]` (even when e.g. borrowed mutably).
         let promotable = match expr_ty.sty {
-            ty::TyArray(_, len) if len.val.to_const_int().unwrap().to_u64().unwrap() == 0 => true,
+            ty::TyArray(_, len) if
+                len.val.to_const_int().and_then(|i| i.to_u64()) == Some(0) => true,
             _ => promotable,
         };
 

src/librustc/mir/mod.rs

@@ -1539,6 +1539,7 @@ fn fmt_const_val<W: Write>(fmt: &mut W, const_val: &ConstVal) -> fmt::Result {
         Variant(def_id) |
         Function(def_id, _) => write!(fmt, "{}", item_path_str(def_id)),
         Aggregate(_) => bug!("`ConstVal::{:?}` should not be in MIR", const_val),
+        Unevaluated(..) => write!(fmt, "{:?}", const_val)
     }
 }
 

src/librustc/traits/error_reporting.rs

@@ -17,6 +17,7 @@ use super::{
     ObligationCauseCode,
     OutputTypeParameterMismatch,
     TraitNotObjectSafe,
+    ConstEvalFailure,
     PredicateObligation,
     Reveal,
     SelectionContext,
@@ -30,6 +31,7 @@ use hir;
 use hir::def_id::DefId;
 use infer::{self, InferCtxt};
 use infer::type_variable::TypeVariableOrigin;
+use middle::const_val;
 use rustc::lint::builtin::EXTRA_REQUIREMENT_IN_IMPL;
 use std::fmt;
 use syntax::ast;
@@ -712,6 +714,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         // (which may fail).
                         span_bug!(span, "WF predicate not satisfied for {:?}", ty);
                     }
+
+                    ty::Predicate::ConstEvaluatable(..) => {
+                        // Errors for `ConstEvaluatable` predicates show up as
+                        // `SelectionError::ConstEvalFailure`,
+                        // not `Unimplemented`.
+                        span_bug!(span,
+                            "const-evaluatable requirement gave wrong error: `{:?}`", obligation)
+                    }
                 }
             }
 
@@ -776,6 +786,13 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 self.tcx.report_object_safety_error(span, did,
                                                     violations)
             }
+
+            ConstEvalFailure(ref err) => {
+                if let const_val::ErrKind::TypeckError = err.kind {
+                    return;
+                }
+                err.struct_error(self.tcx, span, "constant expression")
+            }
         };
         self.note_obligation_cause(&mut err, obligation);
         err.emit();

src/librustc/traits/fulfill.rs

@@ -25,7 +25,7 @@ use super::{FulfillmentError, FulfillmentErrorCode};
 use super::{ObligationCause, PredicateObligation, Obligation};
 use super::project;
 use super::select::SelectionContext;
-use super::Unimplemented;
+use super::{Unimplemented, ConstEvalFailure};
 
 impl<'tcx> ForestObligation for PendingPredicateObligation<'tcx> {
     type Predicate = ty::Predicate<'tcx>;
@@ -540,6 +540,29 @@ fn process_predicate<'a, 'gcx, 'tcx>(
                 }
             }
         }
+
+        ty::Predicate::ConstEvaluatable(def_id, substs) => {
+            match selcx.tcx().lift_to_global(&obligation.param_env) {
+                None => {
+                    Ok(None)
+                }
+                Some(param_env) => {
+                    match selcx.tcx().lift_to_global(&substs) {
+                        None => {
+                            pending_obligation.stalled_on = substs.types().collect();
+                            Ok(None)
+                        }
+                        Some(substs) => {
+                            match selcx.tcx().at(obligation.cause.span)
+                                             .const_eval(param_env.and((def_id, substs))) {
+                                Ok(_) => Ok(Some(vec![])),
+                                Err(e) => Err(CodeSelectionError(ConstEvalFailure(e)))
+                            }
+                        }
+                    }
+                }
+            }
+        }
     }
 }
 

src/librustc/traits/mod.rs

@@ -17,6 +17,7 @@ pub use self::ObligationCauseCode::*;
 
 use hir;
 use hir::def_id::DefId;
+use middle::const_val::ConstEvalErr;
 use middle::region::RegionMaps;
 use middle::free_region::FreeRegionMap;
 use ty::subst::Substs;
@@ -217,6 +218,7 @@ pub enum SelectionError<'tcx> {
                                 ty::PolyTraitRef<'tcx>,
                                 ty::error::TypeError<'tcx>),
     TraitNotObjectSafe(DefId),
+    ConstEvalFailure(ConstEvalErr<'tcx>),
 }
 
 pub struct FulfillmentError<'tcx> {

src/librustc/traits/object_safety.rs

@@ -169,7 +169,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                     ty::Predicate::RegionOutlives(..) |
                     ty::Predicate::ClosureKind(..) |
                     ty::Predicate::Subtype(..) |
-                    ty::Predicate::Equate(..) => {
+                    ty::Predicate::Equate(..) |
+                    ty::Predicate::ConstEvaluatable(..) => {
                         false
                     }
                 }
@@ -203,7 +204,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                     ty::Predicate::WellFormed(..) |
                     ty::Predicate::ObjectSafe(..) |
                     ty::Predicate::ClosureKind(..) |
-                    ty::Predicate::TypeOutlives(..) => {
+                    ty::Predicate::TypeOutlives(..) |
+                    ty::Predicate::ConstEvaluatable(..) => {
                         false
                     }
                 }