1 files changed, 122 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..8ca7e957d
--- /dev/null
+++ b/crates/ra_hir/src/ty/infer/unify.rs
@@ -0,0 +1,122 @@
+//! Unification and canonicalization logic.
+
+use crate::db::HirDatabase;
+use crate::ty::{Ty, Canonical, TraitRef, InferTy};
+use super::InferenceContext;
+
+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(), var_stack: Vec::new() }
+    }
+}
+
+pub(super) struct Canonicalizer<'a, 'b, D: HirDatabase>
+where
+    'a: 'b,
+{
+    ctx: &'b mut InferenceContext<'a, D>,
+    free_vars: Vec<InferTy>,
+    /// A stack of type variables that is used to detect recursive types (which
+    /// are an error, but we need to protect against them to avoid stack
+    /// overflows).
+    var_stack: Vec<super::TypeVarId>,
+}
+
+pub(super) struct Canonicalized<T> {
+    pub value: Canonical<T>,
+    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
+        })
+    }
+
+    fn do_canonicalize_ty(&mut self, ty: Ty) -> Ty {
+        ty.fold(&mut |ty| match ty {
+            Ty::Infer(tv) => {
+                let inner = tv.to_inner();
+                if self.var_stack.contains(&inner) {
+                    // recursive type
+                    return tv.fallback_value();
+                }
+                if let Some(known_ty) = self.ctx.var_unification_table.probe_value(inner).known() {
+                    self.var_stack.push(inner);
+                    let result = self.do_canonicalize_ty(known_ty.clone());
+                    self.var_stack.pop();
+                    result
+                } 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,
+        })
+    }
+
+    fn do_canonicalize_trait_ref(&mut self, trait_ref: TraitRef) -> TraitRef {
+        let substs = trait_ref
+            .substs
+            .iter()
+            .map(|ty| self.do_canonicalize_ty(ty.clone()))
+            .collect::<Vec<_>>();
+        TraitRef { trait_: trait_ref.trait_, substs: substs.into() }
+    }
+
+    fn into_canonicalized<T>(self, result: T) -> Canonicalized<T> {
+        Canonicalized {
+            value: Canonical { value: result, num_vars: self.free_vars.len() },
+            free_vars: self.free_vars,
+        }
+    }
+
+    pub fn canonicalize_ty(mut self, ty: Ty) -> Canonicalized<Ty> {
+        let result = self.do_canonicalize_ty(ty);
+        self.into_canonicalized(result)
+    }
+
+    pub fn canonicalize_trait_ref(mut self, trait_ref: TraitRef) -> Canonicalized<TraitRef> {
+        let result = self.do_canonicalize_trait_ref(trait_ref);
+        self.into_canonicalized(result)
+    }
+}
+
+impl<T> Canonicalized<T> {
+    pub fn decanonicalize_ty(&self, ty: Ty) -> Ty {
+        ty.fold(&mut |ty| match ty {
+            Ty::Bound(idx) => {
+                if (idx as usize) < self.free_vars.len() {
+                    Ty::Infer(self.free_vars[idx as usize].clone())
+                } else {
+                    Ty::Bound(idx)
+                }
+            }
+            ty => ty,
+        })
+    }
+
+    pub fn apply_solution(
+        &self,
+        ctx: &mut InferenceContext<'_, impl HirDatabase>,
+        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(|_| ctx.new_type_var()).collect::<Vec<_>>().into();
+        for (i, ty) in solution.value.into_iter().enumerate() {
+            let var = self.free_vars[i].clone();
+            ctx.unify(&Ty::Infer(var), &ty.subst_bound_vars(&new_vars));
+        }
+    }
+}