Auto merge of #41408 - eddyb:poly-const-eval, r=arielb1

rustc: generalize monomorphic_const_eval to polymorphic constants.

With the addition of `Substs` to the query key, we can now evaluate *and cache* polymorphic constants.

Fixes #23898 by replacing the crippled explicit-discriminant-only local-crate-only `lookup_variant_by_id` with `ConstVal::Variant` which can describe variants irrespective of their discriminant.

Fixes #41394 by fixing #23898 (for the original testcase) and by not looping past the first discriminant.

src/librustc/dep_graph/dep_node.rs

@@ -97,7 +97,7 @@ pub enum DepNode<D: Clone + Debug> {
     TypeckBodiesKrate,
     TypeckTables(D),
     UsedTraitImports(D),
-    MonomorphicConstEval(D),
+    ConstEval(D),
 
     // The set of impls for a given trait. Ultimately, it would be
     // nice to get more fine-grained here (e.g., to include a
@@ -233,7 +233,7 @@ impl<D: Clone + Debug> DepNode<D> {
             InherentImpls(ref d) => op(d).map(InherentImpls),
             TypeckTables(ref d) => op(d).map(TypeckTables),
             UsedTraitImports(ref d) => op(d).map(UsedTraitImports),
-            MonomorphicConstEval(ref d) => op(d).map(MonomorphicConstEval),
+            ConstEval(ref d) => op(d).map(ConstEval),
             TraitImpls(ref d) => op(d).map(TraitImpls),
             TraitItems(ref d) => op(d).map(TraitItems),
             ReprHints(ref d) => op(d).map(ReprHints),

src/librustc/ich/impls_ty.rs

@@ -273,6 +273,12 @@ for ::middle::const_val::ConstVal<'tcx> {
             ConstVal::Bool(value) => {
                 value.hash_stable(hcx, hasher);
             }
+            ConstVal::Char(value) => {
+                value.hash_stable(hcx, hasher);
+            }
+            ConstVal::Variant(def_id) => {
+                def_id.hash_stable(hcx, hasher);
+            }
             ConstVal::Function(def_id, substs) => {
                 def_id.hash_stable(hcx, hasher);
                 substs.hash_stable(hcx, hasher);
@@ -296,9 +302,6 @@ for ::middle::const_val::ConstVal<'tcx> {
                 value.hash_stable(hcx, hasher);
                 times.hash_stable(hcx, hasher);
             }
-            ConstVal::Char(value) => {
-                value.hash_stable(hcx, hasher);
-            }
         }
     }
 }

src/librustc/middle/const_val.rs

@@ -38,12 +38,13 @@ pub enum ConstVal<'tcx> {
     Str(InternedString),
     ByteStr(Rc<Vec<u8>>),
     Bool(bool),
+    Char(char),
+    Variant(DefId),
     Function(DefId, &'tcx Substs<'tcx>),
     Struct(BTreeMap<ast::Name, ConstVal<'tcx>>),
     Tuple(Vec<ConstVal<'tcx>>),
     Array(Vec<ConstVal<'tcx>>),
     Repeat(Box<ConstVal<'tcx>>, u64),
-    Char(char),
 }
 
 impl<'tcx> ConstVal<'tcx> {
@@ -54,12 +55,13 @@ impl<'tcx> ConstVal<'tcx> {
             Str(_) => "string literal",
             ByteStr(_) => "byte string literal",
             Bool(_) => "boolean",
+            Char(..) => "char",
+            Variant(_) => "enum variant",
             Struct(_) => "struct",
             Tuple(_) => "tuple",
             Function(..) => "function definition",
             Array(..) => "array",
             Repeat(..) => "repeat",
-            Char(..) => "char",
         }
     }
 
@@ -85,7 +87,6 @@ pub enum ErrKind<'tcx> {
     MissingStructField,
     NegateOn(ConstVal<'tcx>),
     NotOn(ConstVal<'tcx>),
-    CallOn(ConstVal<'tcx>),
 
     NonConstPath,
     UnimplementedConstVal(&'static str),
@@ -145,7 +146,6 @@ impl<'a, 'gcx, 'tcx> ConstEvalErr<'tcx> {
             CannotCast => simple!("can't cast this type"),
             NegateOn(ref const_val) => simple!("negate on {}", const_val.description()),
             NotOn(ref const_val) => simple!("not on {}", const_val.description()),
-            CallOn(ref const_val) => simple!("call on {}", const_val.description()),
 
             MissingStructField  => simple!("nonexistent struct field"),
             NonConstPath        => simple!("non-constant path in constant expression"),
@@ -227,7 +227,8 @@ pub fn eval_length(tcx: TyCtxt,
 {
     let count_expr = &tcx.hir.body(count).value;
     let count_def_id = tcx.hir.body_owner_def_id(count);
-    match ty::queries::monomorphic_const_eval::get(tcx, count_expr.span, count_def_id) {
+    let substs = Substs::empty();
+    match ty::queries::const_eval::get(tcx, count_expr.span, (count_def_id, substs)) {
         Ok(Integral(Usize(count))) => {
             let val = count.as_u64(tcx.sess.target.uint_type);
             assert_eq!(val as usize as u64, val);

src/librustc/middle/cstore.rs

@@ -249,8 +249,8 @@ pub trait CrateStore {
     fn load_macro(&self, did: DefId, sess: &Session) -> LoadedMacro;
 
     // misc. metadata
-    fn maybe_get_item_body<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, def: DefId)
-                                     -> Option<&'tcx hir::Body>;
+    fn item_body<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, def: DefId)
+                           -> &'tcx hir::Body;
     fn item_body_nested_bodies(&self, def: DefId) -> BTreeMap<hir::BodyId, hir::Body>;
     fn const_is_rvalue_promotable_to_static(&self, def: DefId) -> bool;
 
@@ -399,9 +399,9 @@ impl CrateStore for DummyCrateStore {
     fn load_macro(&self, did: DefId, sess: &Session) -> LoadedMacro { bug!("load_macro") }
 
     // misc. metadata
-    fn maybe_get_item_body<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, def: DefId)
-                                     -> Option<&'tcx hir::Body> {
-        bug!("maybe_get_item_body")
+    fn item_body<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, def: DefId)
+                           -> &'tcx hir::Body {
+        bug!("item_body")
     }
     fn item_body_nested_bodies(&self, def: DefId) -> BTreeMap<hir::BodyId, hir::Body> {
         bug!("item_body_nested_bodies")

src/librustc/mir/mod.rs

@@ -1307,10 +1307,11 @@ fn fmt_const_val<W: Write>(fmt: &mut W, const_val: &ConstVal) -> fmt::Result {
             write!(fmt, "b\"{}\"", escaped)
         }
         Bool(b) => write!(fmt, "{:?}", b),
+        Char(c) => write!(fmt, "{:?}", c),
+        Variant(def_id) |
         Function(def_id, _) => write!(fmt, "{}", item_path_str(def_id)),
         Struct(_) | Tuple(_) | Array(_) | Repeat(..) =>
             bug!("ConstVal `{:?}` should not be in MIR", const_val),
-        Char(c) => write!(fmt, "{:?}", c),
     }
 }
 

src/librustc/ty/maps.rs

@@ -16,6 +16,7 @@ use middle::privacy::AccessLevels;
 use mir;
 use session::CompileResult;
 use ty::{self, CrateInherentImpls, Ty, TyCtxt};
+use ty::subst::Substs;
 use util::nodemap::NodeSet;
 
 use rustc_data_structures::indexed_vec::IndexVec;
@@ -74,6 +75,15 @@ impl Key for (CrateNum, DefId) {
     }
 }
 
+impl<'tcx> Key for (DefId, &'tcx Substs<'tcx>) {
+    fn map_crate(&self) -> CrateNum {
+        self.0.krate
+    }
+    fn default_span(&self, tcx: TyCtxt) -> Span {
+        self.0.default_span(tcx)
+    }
+}
+
 trait Value<'tcx>: Sized {
     fn from_cycle_error<'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self;
 }
@@ -217,6 +227,13 @@ impl<'tcx> QueryDescription for queries::reachable_set<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription for queries::const_eval<'tcx> {
+    fn describe(tcx: TyCtxt, (def_id, _): (DefId, &'tcx Substs<'tcx>)) -> String {
+        format!("const-evaluating `{}`",
+                tcx.item_path_str(def_id))
+    }
+}
+
 macro_rules! define_maps {
     (<$tcx:tt>
      $($(#[$attr:meta])*
@@ -446,16 +463,17 @@ define_maps! { <'tcx>
     /// (Defined only for LOCAL_CRATE)
     pub crate_inherent_impls_overlap_check: crate_inherent_impls_dep_node(CrateNum) -> (),
 
-    /// Results of evaluating monomorphic constants embedded in
-    /// other items, such as enum variant explicit discriminants.
-    pub monomorphic_const_eval: MonomorphicConstEval(DefId) -> const_val::EvalResult<'tcx>,
+    /// Results of evaluating const items or constants embedded in
+    /// other items (such as enum variant explicit discriminants).
+    pub const_eval: const_eval_dep_node((DefId, &'tcx Substs<'tcx>))
+        -> const_val::EvalResult<'tcx>,
 
     /// Performs the privacy check and computes "access levels".
     pub privacy_access_levels: PrivacyAccessLevels(CrateNum) -> Rc<AccessLevels>,
 
     pub reachable_set: reachability_dep_node(CrateNum) -> Rc<NodeSet>,
 
-    pub mir_shims: mir_shim(ty::InstanceDef<'tcx>) -> &'tcx RefCell<mir::Mir<'tcx>>
+    pub mir_shims: mir_shim_dep_node(ty::InstanceDef<'tcx>) -> &'tcx RefCell<mir::Mir<'tcx>>
 }
 
 fn coherent_trait_dep_node((_, def_id): (CrateNum, DefId)) -> DepNode<DefId> {
@@ -470,10 +488,14 @@ fn reachability_dep_node(_: CrateNum) -> DepNode<DefId> {
     DepNode::Reachability
 }
 
-fn mir_shim(instance: ty::InstanceDef) -> DepNode<DefId> {
+fn mir_shim_dep_node(instance: ty::InstanceDef) -> DepNode<DefId> {
     instance.dep_node()
 }
 
 fn typeck_item_bodies_dep_node(_: CrateNum) -> DepNode<DefId> {
     DepNode::TypeckBodiesKrate
 }
+
+fn const_eval_dep_node((def_id, _): (DefId, &Substs)) -> DepNode<DefId> {
+    DepNode::ConstEval(def_id)
+}

src/librustc/ty/mod.rs

@@ -1693,6 +1693,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         }
     }
 
+    #[inline]
     pub fn discriminants(&'a self, tcx: TyCtxt<'a, 'gcx, 'tcx>)
                          -> impl Iterator<Item=ConstInt> + 'a {
         let repr_type = self.repr.discr_type();
@@ -1701,11 +1702,18 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         self.variants.iter().map(move |v| {
             let mut discr = prev_discr.map_or(initial, |d| d.wrap_incr());
             if let VariantDiscr::Explicit(expr_did) = v.discr {
-                match queries::monomorphic_const_eval::get(tcx, DUMMY_SP, expr_did) {
+                let substs = Substs::empty();
+                match queries::const_eval::get(tcx, DUMMY_SP, (expr_did, substs)) {
                     Ok(ConstVal::Integral(v)) => {
                         discr = v;
                     }
-                    _ => {}
+                    err => {
+                        if !expr_did.is_local() {
+                            span_bug!(tcx.def_span(expr_did),
+                                "variant discriminant evaluation succeeded \
+                                 in its crate but failed locally: {:?}", err);
+                        }
+                    }
                 }
             }
             prev_discr = Some(discr);
@@ -1733,12 +1741,21 @@ impl<'a, 'gcx, 'tcx> AdtDef {
                     explicit_index -= distance;
                 }
                 ty::VariantDiscr::Explicit(expr_did) => {
-                    match queries::monomorphic_const_eval::get(tcx, DUMMY_SP, expr_did) {
+                    let substs = Substs::empty();
+                    match queries::const_eval::get(tcx, DUMMY_SP, (expr_did, substs)) {
                         Ok(ConstVal::Integral(v)) => {
                             explicit_value = v;
                             break;
                         }
-                        _ => {
+                        err => {
+                            if !expr_did.is_local() {
+                                span_bug!(tcx.def_span(expr_did),
+                                    "variant discriminant evaluation succeeded \
+                                     in its crate but failed locally: {:?}", err);
+                            }
+                            if explicit_index == 0 {
+                                break;
+                            }
                             explicit_index -= 1;
                         }
                     }