Remove ty::BrFresh and new_bound

[rust.git] / src / librustc / infer / unify_key.rs

diff --git a/src/librustc/infer/unify_key.rs b/src/librustc/infer/unify_key.rs
index 09f800d9f9bfc97d8fce3c80dfacc95279a77928..678a45a84e9eafc9dac86a21ca8555b311fc23e4 100644 (file)
--- a/src/librustc/infer/unify_key.rs
+++ b/src/librustc/infer/unify_key.rs
@@ -1,5 +1,13 @@
-use crate::ty::{self, FloatVarValue, IntVarValue, Ty, TyCtxt};
-use rustc_data_structures::unify::{NoError, EqUnifyValue, UnifyKey, UnifyValue};
+use crate::ty::{self, FloatVarValue, IntVarValue, Ty, TyCtxt, InferConst};
+use crate::mir::interpret::ConstValue;
+use rustc_data_structures::unify::{NoError, EqUnifyValue, UnifyKey, UnifyValue, UnificationTable};
+use rustc_data_structures::unify::InPlace;
+use syntax_pos::{Span, DUMMY_SP};
+use syntax::symbol::InternedString;
+
+use std::cmp;
+use std::marker::PhantomData;
+use std::cell::RefMut;
 
 pub trait ToType {
     fn to_type<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx>;
@@ -12,8 +20,7 @@ fn from_index(i: u32) -> ty::IntVid { ty::IntVid { index: i } }
     fn tag() -> &'static str { "IntVid" }
 }
 
-impl EqUnifyValue for IntVarValue {
-}
+impl EqUnifyValue for IntVarValue {}
 
 #[derive(PartialEq, Copy, Clone, Debug)]
 pub struct RegionVidKey {
@@ -62,11 +69,114 @@ fn from_index(i: u32) -> ty::FloatVid { ty::FloatVid { index: i } }
     fn tag() -> &'static str { "FloatVid" }
 }
 
-impl EqUnifyValue for FloatVarValue {
-}
+impl EqUnifyValue for FloatVarValue {}
 
 impl ToType for FloatVarValue {
     fn to_type<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
         tcx.mk_mach_float(self.0)
     }
 }
+
+// Generic consts.
+
+/// Reasons to create a const inference variable
+#[derive(Copy, Clone, Debug)]
+pub enum ConstVariableOrigin {
+    MiscVariable(Span),
+    ConstInference(Span),
+    ConstParameterDefinition(Span, InternedString),
+    SubstitutionPlaceholder(Span),
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum ConstVariableValue<'tcx> {
+    Known { value: &'tcx 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<&'tcx ty::Const<'tcx>> {
+        match *self {
+            ConstVariableValue::Unknown { .. } => None,
+            ConstVariableValue::Known { value } => Some(value),
+        }
+    }
+
+    pub fn is_unknown(&self) -> bool {
+        match *self {
+            ConstVariableValue::Unknown { .. } => true,
+            ConstVariableValue::Known { .. } => false,
+        }
+    }
+}
+
+#[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>;
+    fn index(&self) -> u32 { self.index }
+    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 = (&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>);
+
+    fn unify_values(value1: &Self, value2: &Self) -> Result<Self, Self::Error> {
+        let val = 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 { .. }) => {
+                Ok(value1.val)
+            }
+            (ConstVariableValue::Unknown { .. }, ConstVariableValue::Known { .. }) => {
+                Ok(value2.val)
+            }
+
+            // 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);
+                Ok(ConstVariableValue::Unknown { universe })
+            }
+        }?;
+
+        Ok(ConstVarValue {
+            origin: ConstVariableOrigin::ConstInference(DUMMY_SP),
+            val,
+        })
+    }
+}
+
+impl<'tcx> EqUnifyValue for &'tcx ty::Const<'tcx> {}
+
+pub fn replace_if_possible(
+    mut table: RefMut<'_, UnificationTable<InPlace<ty::ConstVid<'tcx>>>>,
+    c: &'tcx ty::Const<'tcx>
+) -> &'tcx ty::Const<'tcx> {
+    if let ty::Const { val: ConstValue::Infer(InferConst::Var(vid)), .. } = c {
+        match table.probe_value(*vid).val.known() {
+            Some(c) => c,
+            None => c,
+        }
+    } else {
+        c
+    }
+}