1 files changed, 152 insertions, 0 deletions
diff --git a/vendor/chalk-solve-0.87.0/src/infer/var.rs b/vendor/chalk-solve-0.87.0/src/infer/var.rs
new file mode 100644
index 000000000..3fbf92002
--- /dev/null
+++ b/vendor/chalk-solve-0.87.0/src/infer/var.rs
@@ -0,0 +1,152 @@
+use chalk_ir::cast::Cast;
+use chalk_ir::interner::Interner;
+use chalk_ir::*;
+use ena::unify::{UnifyKey, UnifyValue};
+use std::cmp::min;
+use std::fmt;
+use std::marker::PhantomData;
+use std::u32;
+
+/// Wrapper around `chalk_ir::InferenceVar` for coherence purposes.
+/// An inference variable represents an unknown term -- either a type
+/// or a lifetime. The variable itself is just an index into the
+/// unification table; the unification table maps it to an
+/// `InferenceValue`.
+///
+/// Inference variables can be in one of two states (represents by the variants
+/// of an `InferenceValue`):
+///
+/// - Unbound(`ui`). In this case, the value of the variable is not yet known. We carry
+///   along a universe index `ui` that tracks the universe in which the variable was
+///   created; this determines what names may appear in the variable's value.
+///   - In this state, we do **not** track the kind of this variable
+///     (i.e., whether it represents a type or a lifetime). There is
+///     no need: if it represents a lifetime, for example, then there
+///     should only ever be constraints that relate it to other
+///     lifetimes, or use it in lifetime position.
+/// - Bound. In this case, the value of the variable is known. We
+///   carry along the value. We discard the universe index in which
+///   the variable was created, since that was only needed to help us
+///   reject illegal values. Once the value of a variable is known, it
+///   can never change.
+///   - The value we actually store for variables is a
+///     `ir::GenericArg`, and hence it does carry along the kind of the
+///     variable via the enum variant. However, we should always know
+///     the kind of the variable from context, and hence we typically
+///     "downcast" the resulting variable using
+///     e.g. `value.ty().unwrap()`.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct EnaVariable<I: Interner> {
+    var: InferenceVar,
+    phantom: PhantomData<I>,
+}
+
+impl<I: Interner> From<InferenceVar> for EnaVariable<I> {
+    fn from(var: InferenceVar) -> EnaVariable<I> {
+        EnaVariable {
+            var,
+            phantom: PhantomData,
+        }
+    }
+}
+
+impl<I: Interner> From<EnaVariable<I>> for InferenceVar {
+    fn from(ena_var: EnaVariable<I>) -> InferenceVar {
+        ena_var.var
+    }
+}
+
+impl<I: Interner> EnaVariable<I> {
+    /// Convert this inference variable into a type. When using this
+    /// method, naturally you should know from context that the kind
+    /// of this inference variable is a type (we can't check it).
+    pub fn to_ty_with_kind(self, interner: I, kind: TyVariableKind) -> Ty<I> {
+        self.var.to_ty(interner, kind)
+    }
+
+    /// Same as `to_ty_with_kind`, but the kind is set to `TyVariableKind::General`.
+    /// This should be used instead of `to_ty_with_kind` when creating a new
+    /// inference variable (when the kind is not known).
+    pub fn to_ty(self, interner: I) -> Ty<I> {
+        self.var.to_ty(interner, TyVariableKind::General)
+    }
+
+    /// Convert this inference variable into a lifetime. When using this
+    /// method, naturally you should know from context that the kind
+    /// of this inference variable is a lifetime (we can't check it).
+    pub fn to_lifetime(self, interner: I) -> Lifetime<I> {
+        self.var.to_lifetime(interner)
+    }
+
+    /// Convert this inference variable into a const. When using this
+    /// method, naturally you should know from context that the kind
+    /// of this inference variable is a const (we can't check it).
+    pub fn to_const(self, interner: I, ty: Ty<I>) -> Const<I> {
+        self.var.to_const(interner, ty)
+    }
+}
+
+impl<I: Interner> UnifyKey for EnaVariable<I> {
+    type Value = InferenceValue<I>;
+
+    fn index(&self) -> u32 {
+        self.var.index()
+    }
+
+    fn from_index(u: u32) -> Self {
+        EnaVariable::from(InferenceVar::from(u))
+    }
+
+    fn tag() -> &'static str {
+        "EnaVariable"
+    }
+}
+
+/// The value of an inference variable. We start out as `Unbound` with a
+/// universe index; when the inference variable is assigned a value, it becomes
+/// bound and records that value. See `EnaVariable` for more details.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum InferenceValue<I: Interner> {
+    Unbound(UniverseIndex),
+    Bound(GenericArg<I>),
+}
+
+impl<I: Interner> InferenceValue<I> {
+    pub fn from_ty(interner: I, ty: Ty<I>) -> Self {
+        InferenceValue::Bound(ty.cast(interner))
+    }
+
+    pub fn from_lifetime(interner: I, lifetime: Lifetime<I>) -> Self {
+        InferenceValue::Bound(lifetime.cast(interner))
+    }
+
+    pub fn from_const(interner: I, constant: Const<I>) -> Self {
+        InferenceValue::Bound(constant.cast(interner))
+    }
+}
+
+impl<I: Interner> UnifyValue for InferenceValue<I> {
+    type Error = (InferenceValue<I>, InferenceValue<I>);
+
+    fn unify_values(
+        a: &InferenceValue<I>,
+        b: &InferenceValue<I>,
+    ) -> Result<InferenceValue<I>, (InferenceValue<I>, InferenceValue<I>)> {
+        match (a, b) {
+            (&InferenceValue::Unbound(ui_a), &InferenceValue::Unbound(ui_b)) => {
+                Ok(InferenceValue::Unbound(min(ui_a, ui_b)))
+            }
+            (bound @ &InferenceValue::Bound(_), &InferenceValue::Unbound(_))
+            | (&InferenceValue::Unbound(_), bound @ &InferenceValue::Bound(_)) => Ok(bound.clone()),
+            (&InferenceValue::Bound(_), &InferenceValue::Bound(_)) => {
+                panic!("we should not be asked to unify two bound things")
+            }
+        }
+    }
+}
+
+impl<I: Interner> fmt::Debug for EnaVariable<I> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", self.var)
+    }
+}