1 files changed, 162 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/infer/unify_key.rs b/compiler/rustc_middle/src/infer/unify_key.rs
new file mode 100644
index 000000000..f2627885d
--- /dev/null
+++ b/compiler/rustc_middle/src/infer/unify_key.rs
@@ -0,0 +1,162 @@
+use crate::ty::{self, Ty, TyCtxt};
+use rustc_data_structures::unify::{NoError, UnifyKey, UnifyValue};
+use rustc_span::def_id::DefId;
+use rustc_span::symbol::Symbol;
+use rustc_span::Span;
+use std::cmp;
+use std::marker::PhantomData;
+
+pub trait ToType {
+    fn to_type<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
+}
+
+#[derive(PartialEq, Copy, Clone, Debug)]
+pub struct UnifiedRegion<'tcx>(pub Option<ty::Region<'tcx>>);
+
+#[derive(PartialEq, Copy, Clone, Debug)]
+pub struct RegionVidKey<'tcx> {
+    pub vid: ty::RegionVid,
+    pub phantom: PhantomData<UnifiedRegion<'tcx>>,
+}
+
+impl<'tcx> From<ty::RegionVid> for RegionVidKey<'tcx> {
+    fn from(vid: ty::RegionVid) -> Self {
+        RegionVidKey { vid, phantom: PhantomData }
+    }
+}
+
+impl<'tcx> UnifyKey for RegionVidKey<'tcx> {
+    type Value = UnifiedRegion<'tcx>;
+    #[inline]
+    fn index(&self) -> u32 {
+        self.vid.as_u32()
+    }
+    #[inline]
+    fn from_index(i: u32) -> Self {
+        RegionVidKey::from(ty::RegionVid::from_u32(i))
+    }
+    fn tag() -> &'static str {
+        "RegionVidKey"
+    }
+}
+
+impl<'tcx> UnifyValue for UnifiedRegion<'tcx> {
+    type Error = NoError;
+
+    fn unify_values(value1: &Self, value2: &Self) -> Result<Self, NoError> {
+        Ok(match (value1.0, value2.0) {
+            // Here we can just pick one value, because the full constraints graph
+            // will be handled later. Ideally, we might want a `MultipleValues`
+            // variant or something. For now though, this is fine.
+            (Some(_), Some(_)) => *value1,
+
+            (Some(_), _) => *value1,
+            (_, Some(_)) => *value2,
+
+            (None, None) => *value1,
+        })
+    }
+}
+
+impl ToType for ty::IntVarValue {
+    fn to_type<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        match *self {
+            ty::IntType(i) => tcx.mk_mach_int(i),
+            ty::UintType(i) => tcx.mk_mach_uint(i),
+        }
+    }
+}
+
+impl ToType for ty::FloatVarValue {
+    fn to_type<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        tcx.mk_mach_float(self.0)
+    }
+}
+
+// Generic consts.
+
+#[derive(Copy, Clone, Debug)]
+pub struct ConstVariableOrigin {
+    pub kind: ConstVariableOriginKind,
+    pub span: Span,
+}
+
+/// Reasons to create a const inference variable
+#[derive(Copy, Clone, Debug)]
+pub enum ConstVariableOriginKind {
+    MiscVariable,
+    ConstInference,
+    ConstParameterDefinition(Symbol, DefId),
+    SubstitutionPlaceholder,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum ConstVariableValue<'tcx> {
+    Known { value: ty::Const<'tcx> },
+    Unknown { universe: ty::UniverseIndex },
+}
+
+impl<'tcx> ConstVariableValue<'tcx> {
+    /// If this value is known, returns the const it is known to be.
+    /// Otherwise, `None`.
+    pub fn known(&self) -> Option<ty::Const<'tcx>> {
+        match *self {
+            ConstVariableValue::Unknown { .. } => None,
+            ConstVariableValue::Known { value } => Some(value),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct ConstVarValue<'tcx> {
+    pub origin: ConstVariableOrigin,
+    pub val: ConstVariableValue<'tcx>,
+}
+
+impl<'tcx> UnifyKey for ty::ConstVid<'tcx> {
+    type Value = ConstVarValue<'tcx>;
+    #[inline]
+    fn index(&self) -> u32 {
+        self.index
+    }
+    #[inline]
+    fn from_index(i: u32) -> Self {
+        ty::ConstVid { index: i, phantom: PhantomData }
+    }
+    fn tag() -> &'static str {
+        "ConstVid"
+    }
+}
+
+impl<'tcx> UnifyValue for ConstVarValue<'tcx> {
+    type Error = (ty::Const<'tcx>, ty::Const<'tcx>);
+
+    fn unify_values(&value1: &Self, &value2: &Self) -> Result<Self, Self::Error> {
+        Ok(match (value1.val, value2.val) {
+            (ConstVariableValue::Known { .. }, ConstVariableValue::Known { .. }) => {
+                bug!("equating two const variables, both of which have known values")
+            }
+
+            // If one side is known, prefer that one.
+            (ConstVariableValue::Known { .. }, ConstVariableValue::Unknown { .. }) => value1,
+            (ConstVariableValue::Unknown { .. }, ConstVariableValue::Known { .. }) => value2,
+
+            // If both sides are *unknown*, it hardly matters, does it?
+            (
+                ConstVariableValue::Unknown { universe: universe1 },
+                ConstVariableValue::Unknown { universe: universe2 },
+            ) => {
+                // If we unify two unbound variables, ?T and ?U, then whatever
+                // value they wind up taking (which must be the same value) must
+                // be nameable by both universes. Therefore, the resulting
+                // universe is the minimum of the two universes, because that is
+                // the one which contains the fewest names in scope.
+                let universe = cmp::min(universe1, universe2);
+                ConstVarValue {
+                    val: ConstVariableValue::Unknown { universe },
+                    origin: value1.origin,
+                }
+            }
+        })
+    }
+}