Chalk integration

 - add proper canonicalization logic
 - add conversions from/to Chalk IR

1 files changed, 81 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/infer/unify.rs b/crates/ra_hir/src/ty/infer/unify.rs
new file mode 100644
index 000000000..7918b007b
--- /dev/null
+++ b/crates/ra_hir/src/ty/infer/unify.rs
@@ -0,0 +1,81 @@
+//! Unification and canonicalization logic.
+
+use super::{InferenceContext, Ty, TraitRef, InferTy, HirDatabase};
+
+impl<'a, D: HirDatabase> InferenceContext<'a, D> {
+    pub(super) fn canonicalizer<'b>(&'b mut self) -> Canonicalizer<'a, 'b, D>
+    where
+        'a: 'b,
+    {
+        Canonicalizer { ctx: self, free_vars: Vec::new() }
+    }
+}
+
+// TODO improve the interface of this
+
+// TODO move further up?
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub(crate) struct Canonical<T> {
+    pub value: T,
+    pub num_vars: usize,
+}
+
+pub(super) struct Canonicalizer<'a, 'b, D: HirDatabase>
+where
+    'a: 'b,
+{
+    pub ctx: &'b mut InferenceContext<'a, D>,
+    pub free_vars: Vec<InferTy>,
+}
+
+impl<'a, 'b, D: HirDatabase> Canonicalizer<'a, 'b, D>
+where
+    'a: 'b,
+{
+    fn add(&mut self, free_var: InferTy) -> usize {
+        self.free_vars.iter().position(|&v| v == free_var).unwrap_or_else(|| {
+            let next_index = self.free_vars.len();
+            self.free_vars.push(free_var);
+            next_index
+        })
+    }
+
+    pub fn canonicalize_ty(&mut self, ty: Ty) -> Canonical<Ty> {
+        let value = ty.fold(&mut |ty| match ty {
+            Ty::Infer(tv) => {
+                let inner = tv.to_inner();
+                // TODO prevent infinite loops? => keep var stack
+                if let Some(known_ty) = self.ctx.var_unification_table.probe_value(inner).known() {
+                    self.canonicalize_ty(known_ty.clone()).value
+                } else {
+                    let free_var = InferTy::TypeVar(self.ctx.var_unification_table.find(inner));
+                    let position = self.add(free_var);
+                    Ty::Bound(position as u32)
+                }
+            }
+            _ => ty,
+        });
+        Canonical { value, num_vars: self.free_vars.len() }
+    }
+
+    pub fn canonicalize_trait_ref(&mut self, trait_ref: TraitRef) -> Canonical<TraitRef> {
+        let substs = trait_ref
+            .substs
+            .0
+            .iter()
+            .map(|ty| self.canonicalize_ty(ty.clone()).value)
+            .collect::<Vec<_>>();
+        let value = TraitRef { trait_: trait_ref.trait_, substs: substs.into() };
+        Canonical { value, num_vars: self.free_vars.len() }
+    }
+
+    pub fn apply_solution(&mut self, solution: Canonical<Vec<Ty>>) {
+        // the solution may contain new variables, which we need to convert to new inference vars
+        let new_vars =
+            (0..solution.num_vars).map(|_| self.ctx.new_type_var()).collect::<Vec<_>>().into();
+        for (i, ty) in solution.value.into_iter().enumerate() {
+            let var = self.free_vars[i].clone();
+            self.ctx.unify(&Ty::Infer(var), &ty.subst_bound_vars(&new_vars));
+        }
+    }
+}