Implement Chalk variable kinds

This means we need to keep track of the kinds (general/int/float) of variables
in `Canonical`, which requires some more ceremony. (It also exposes some places
where we're not really dealing with canonicalization correctly -- another thing
to be cleaned up when we switch to using Chalk's types directly.)

Should fix the last remaining issue of #2534.

7 files changed, 135 insertions, 66 deletions

diff --git a/crates/ra_hir_ty/src/autoderef.rs b/crates/ra_hir_ty/src/autoderef.rs
index 1b0f84c5c..c727012c6 100644
--- a/crates/ra_hir_ty/src/autoderef.rs
+++ b/crates/ra_hir_ty/src/autoderef.rs
@@ -37,7 +37,7 @@ pub(crate) fn deref(
     ty: InEnvironment<&Canonical<Ty>>,
 ) -> Option<Canonical<Ty>> {
     if let Some(derefed) = ty.value.value.builtin_deref() {
-        Some(Canonical { value: derefed, num_vars: ty.value.num_vars })
+        Some(Canonical { value: derefed, kinds: ty.value.kinds.clone() })
     } else {
         deref_by_trait(db, krate, ty)
     }
@@ -68,8 +68,8 @@ fn deref_by_trait(
 
     // Check that the type implements Deref at all
     let trait_ref = TraitRef { trait_: deref_trait, substs: parameters.clone() };
-    let implements_goal = super::Canonical {
-        num_vars: ty.value.num_vars,
+    let implements_goal = Canonical {
+        kinds: ty.value.kinds.clone(),
         value: InEnvironment {
             value: Obligation::Trait(trait_ref),
             environment: ty.environment.clone(),
@@ -81,7 +81,7 @@ fn deref_by_trait(
 
     // Now do the assoc type projection
     let projection = super::traits::ProjectionPredicate {
-        ty: Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, ty.value.num_vars)),
+        ty: Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, ty.value.kinds.len())),
         projection_ty: super::ProjectionTy { associated_ty: target, parameters },
     };
 
@@ -89,7 +89,8 @@ fn deref_by_trait(
 
     let in_env = InEnvironment { value: obligation, environment: ty.environment };
 
-    let canonical = super::Canonical { num_vars: 1 + ty.value.num_vars, value: in_env };
+    let canonical =
+        Canonical::new(in_env, ty.value.kinds.iter().copied().chain(Some(super::TyKind::General)));
 
     let solution = db.trait_solve(krate, canonical)?;
 
@@ -110,7 +111,7 @@ fn deref_by_trait(
             // assumptions will be broken. We would need to properly introduce
             // new variables in that case
 
-            for i in 1..vars.0.num_vars {
+            for i in 1..vars.0.kinds.len() {
                 if vars.0.value[i - 1] != Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, i - 1))
                 {
                     warn!("complex solution for derefing {:?}: {:?}, ignoring", ty.value, solution);
@@ -119,7 +120,7 @@ fn deref_by_trait(
             }
             Some(Canonical {
                 value: vars.0.value[vars.0.value.len() - 1].clone(),
-                num_vars: vars.0.num_vars,
+                kinds: vars.0.kinds.clone(),
             })
         }
         Solution::Ambig(_) => {
diff --git a/crates/ra_hir_ty/src/infer/unify.rs b/crates/ra_hir_ty/src/infer/unify.rs
index 269495ca0..2e895d911 100644
--- a/crates/ra_hir_ty/src/infer/unify.rs
+++ b/crates/ra_hir_ty/src/infer/unify.rs
@@ -9,7 +9,7 @@ use test_utils::mark;
 use super::{InferenceContext, Obligation};
 use crate::{
     BoundVar, Canonical, DebruijnIndex, GenericPredicate, InEnvironment, InferTy, Substs, Ty,
-    TypeCtor, TypeWalk,
+    TyKind, TypeCtor, TypeWalk,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -86,10 +86,20 @@ where
     }
 
     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,
-        }
+        let kinds = self
+            .free_vars
+            .iter()
+            .map(|v| match v {
+                // mapping MaybeNeverTypeVar to the same kind as general ones
+                // should be fine, because as opposed to int or float type vars,
+                // they don't restrict what kind of type can go into them, they
+                // just affect fallback.
+                InferTy::TypeVar(_) | InferTy::MaybeNeverTypeVar(_) => TyKind::General,
+                InferTy::IntVar(_) => TyKind::Integer,
+                InferTy::FloatVar(_) => TyKind::Float,
+            })
+            .collect();
+        Canonicalized { value: Canonical { value: result, kinds }, free_vars: self.free_vars }
     }
 
     pub(crate) fn canonicalize_ty(mut self, ty: Ty) -> Canonicalized<Ty> {
@@ -131,26 +141,41 @@ impl<T> Canonicalized<T> {
         ty
     }
 
-    pub fn apply_solution(&self, ctx: &mut InferenceContext<'_>, solution: Canonical<Vec<Ty>>) {
+    pub fn apply_solution(&self, ctx: &mut InferenceContext<'_>, solution: Canonical<Substs>) {
         // the solution may contain new variables, which we need to convert to new inference vars
-        let new_vars = Substs((0..solution.num_vars).map(|_| ctx.table.new_type_var()).collect());
+        let new_vars = Substs(
+            solution
+                .kinds
+                .iter()
+                .map(|k| match k {
+                    TyKind::General => ctx.table.new_type_var(),
+                    TyKind::Integer => ctx.table.new_integer_var(),
+                    TyKind::Float => ctx.table.new_float_var(),
+                })
+                .collect(),
+        );
         for (i, ty) in solution.value.into_iter().enumerate() {
             let var = self.free_vars[i];
             // eagerly replace projections in the type; we may be getting types
             // e.g. from where clauses where this hasn't happened yet
-            let ty = ctx.normalize_associated_types_in(ty.subst_bound_vars(&new_vars));
+            let ty = ctx.normalize_associated_types_in(ty.clone().subst_bound_vars(&new_vars));
             ctx.table.unify(&Ty::Infer(var), &ty);
         }
     }
 }
 
-pub fn unify(ty1: &Canonical<Ty>, ty2: &Canonical<Ty>) -> Option<Substs> {
+pub fn unify(tys: &Canonical<(Ty, Ty)>) -> Option<Substs> {
     let mut table = InferenceTable::new();
-    let num_vars = ty1.num_vars.max(ty2.num_vars);
-    let vars =
-        Substs::builder(num_vars).fill(std::iter::repeat_with(|| table.new_type_var())).build();
-    let ty1_with_vars = ty1.value.clone().subst_bound_vars(&vars);
-    let ty2_with_vars = ty2.value.clone().subst_bound_vars(&vars);
+    let vars = Substs(
+        tys.kinds
+            .iter()
+            // we always use type vars here because we want everything to
+            // fallback to Unknown in the end (kind of hacky, as below)
+            .map(|_| table.new_type_var())
+            .collect(),
+    );
+    let ty1_with_vars = tys.value.0.clone().subst_bound_vars(&vars);
+    let ty2_with_vars = tys.value.1.clone().subst_bound_vars(&vars);
     if !table.unify(&ty1_with_vars, &ty2_with_vars) {
         return None;
     }
@@ -162,7 +187,7 @@ pub fn unify(ty1: &Canonical<Ty>, ty2: &Canonical<Ty>) -> Option<Substs> {
         }
     }
     Some(
-        Substs::builder(ty1.num_vars)
+        Substs::builder(tys.kinds.len())
             .fill(vars.iter().map(|v| table.resolve_ty_completely(v.clone())))
             .build(),
     )
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index c9513b752..7f3f5e771 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -662,13 +662,27 @@ impl TypeWalk for GenericPredicate {
 
 /// Basically a claim (currently not validated / checked) that the contained
 /// type / trait ref contains no inference variables; any inference variables it
-/// contained have been replaced by bound variables, and `num_vars` tells us how
-/// many there are. This is used to erase irrelevant differences between types
-/// before using them in queries.
+/// contained have been replaced by bound variables, and `kinds` tells us how
+/// many there are and whether they were normal or float/int variables. This is
+/// used to erase irrelevant differences between types before using them in
+/// queries.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Canonical<T> {
     pub value: T,
-    pub num_vars: usize,
+    pub kinds: Arc<[TyKind]>,
+}
+
+impl<T> Canonical<T> {
+    pub fn new(value: T, kinds: impl IntoIterator<Item = TyKind>) -> Self {
+        Self { value, kinds: kinds.into_iter().collect() }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum TyKind {
+    General,
+    Integer,
+    Float,
 }
 
 /// A function signature as seen by type inference: Several parameter types and
diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
index c19519cf1..c3edd6885 100644
--- a/crates/ra_hir_ty/src/method_resolution.rs
+++ b/crates/ra_hir_ty/src/method_resolution.rs
@@ -2,7 +2,7 @@
 //! For details about how this works in rustc, see the method lookup page in the
 //! [rustc guide](https://rust-lang.github.io/rustc-guide/method-lookup.html)
 //! and the corresponding code mostly in librustc_typeck/check/method/probe.rs.
-use std::sync::Arc;
+use std::{iter, sync::Arc};
 
 use arrayvec::ArrayVec;
 use hir_def::{
@@ -17,7 +17,8 @@ use rustc_hash::{FxHashMap, FxHashSet};
 use super::Substs;
 use crate::{
     autoderef, db::HirDatabase, primitive::FloatBitness, utils::all_super_traits, ApplicationTy,
-    Canonical, DebruijnIndex, InEnvironment, TraitEnvironment, TraitRef, Ty, TypeCtor, TypeWalk,
+    Canonical, DebruijnIndex, InEnvironment, TraitEnvironment, TraitRef, Ty, TyKind, TypeCtor,
+    TypeWalk,
 };
 
 /// This is used as a key for indexing impls.
@@ -377,7 +378,7 @@ fn iterate_method_candidates_with_autoref(
         return true;
     }
     let refed = Canonical {
-        num_vars: deref_chain[0].num_vars,
+        kinds: deref_chain[0].kinds.clone(),
         value: Ty::apply_one(TypeCtor::Ref(Mutability::Shared), deref_chain[0].value.clone()),
     };
     if iterate_method_candidates_by_receiver(
@@ -393,7 +394,7 @@ fn iterate_method_candidates_with_autoref(
         return true;
     }
     let ref_muted = Canonical {
-        num_vars: deref_chain[0].num_vars,
+        kinds: deref_chain[0].kinds.clone(),
         value: Ty::apply_one(TypeCtor::Ref(Mutability::Mut), deref_chain[0].value.clone()),
     };
     if iterate_method_candidates_by_receiver(
@@ -612,18 +613,19 @@ pub(crate) fn inherent_impl_substs(
     // we create a var for each type parameter of the impl; we need to keep in
     // mind here that `self_ty` might have vars of its own
     let vars = Substs::build_for_def(db, impl_id)
-        .fill_with_bound_vars(DebruijnIndex::INNERMOST, self_ty.num_vars)
+        .fill_with_bound_vars(DebruijnIndex::INNERMOST, self_ty.kinds.len())
         .build();
     let self_ty_with_vars = db.impl_self_ty(impl_id).subst(&vars);
-    let self_ty_with_vars =
-        Canonical { num_vars: vars.len() + self_ty.num_vars, value: self_ty_with_vars };
-    let substs = super::infer::unify(&self_ty_with_vars, self_ty);
+    let mut kinds = self_ty.kinds.to_vec();
+    kinds.extend(iter::repeat(TyKind::General).take(vars.len()));
+    let tys = Canonical { kinds: kinds.into(), value: (self_ty_with_vars, self_ty.value.clone()) };
+    let substs = super::infer::unify(&tys);
     // We only want the substs for the vars we added, not the ones from self_ty.
     // Also, if any of the vars we added are still in there, we replace them by
     // Unknown. I think this can only really happen if self_ty contained
     // Unknown, and in that case we want the result to contain Unknown in those
     // places again.
-    substs.map(|s| fallback_bound_vars(s.suffix(vars.len()), self_ty.num_vars))
+    substs.map(|s| fallback_bound_vars(s.suffix(vars.len()), self_ty.kinds.len()))
 }
 
 /// This replaces any 'free' Bound vars in `s` (i.e. those with indices past
@@ -683,15 +685,15 @@ fn generic_implements_goal(
     trait_: TraitId,
     self_ty: Canonical<Ty>,
 ) -> Canonical<InEnvironment<super::Obligation>> {
-    let num_vars = self_ty.num_vars;
+    let mut kinds = self_ty.kinds.to_vec();
     let substs = super::Substs::build_for_def(db, trait_)
         .push(self_ty.value)
-        .fill_with_bound_vars(DebruijnIndex::INNERMOST, num_vars)
+        .fill_with_bound_vars(DebruijnIndex::INNERMOST, kinds.len())
         .build();
-    let num_vars = substs.len() - 1 + self_ty.num_vars;
+    kinds.extend(iter::repeat(TyKind::General).take(substs.len() - 1));
     let trait_ref = TraitRef { trait_, substs };
     let obligation = super::Obligation::Trait(trait_ref);
-    Canonical { num_vars, value: InEnvironment::new(env, obligation) }
+    Canonical { kinds: kinds.into(), value: InEnvironment::new(env, obligation) }
 }
 
 fn autoderef_method_receiver(
@@ -704,9 +706,9 @@ fn autoderef_method_receiver(
     if let Some(Ty::Apply(ApplicationTy { ctor: TypeCtor::Array, parameters })) =
         deref_chain.last().map(|ty| &ty.value)
     {
-        let num_vars = deref_chain.last().unwrap().num_vars;
+        let kinds = deref_chain.last().unwrap().kinds.clone();
         let unsized_ty = Ty::apply(TypeCtor::Slice, parameters.clone());
-        deref_chain.push(Canonical { value: unsized_ty, num_vars })
+        deref_chain.push(Canonical { value: unsized_ty, kinds })
     }
     deref_chain
 }
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index 01c919a7e..766790576 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -3029,3 +3029,21 @@ fn infer_dyn_fn_output() {
     "###
     );
 }
+
+#[test]
+fn variable_kinds() {
+    check_types(
+        r#"
+trait Trait<T> { fn get(self, t: T) -> T; }
+struct S;
+impl Trait<u128> for S {}
+impl Trait<f32> for S {}
+fn test() {
+    S.get(1);
+  //^^^^^^^^ u128
+    S.get(1.);
+  //^^^^^^^^ f32
+}
+        "#,
+    );
+}
diff --git a/crates/ra_hir_ty/src/traits.rs b/crates/ra_hir_ty/src/traits.rs
index 6f43c3a22..2a6d7faef 100644
--- a/crates/ra_hir_ty/src/traits.rs
+++ b/crates/ra_hir_ty/src/traits.rs
@@ -1,5 +1,5 @@
 //! Trait solving using Chalk.
-use std::{panic, sync::Arc};
+use std::sync::Arc;
 
 use chalk_ir::cast::Cast;
 use hir_def::{
@@ -8,7 +8,7 @@ use hir_def::{
 use ra_db::{impl_intern_key, salsa, CrateId};
 use ra_prof::profile;
 
-use crate::{db::HirDatabase, DebruijnIndex};
+use crate::{db::HirDatabase, DebruijnIndex, Substs};
 
 use super::{Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty, TypeWalk};
 
@@ -190,15 +190,7 @@ fn solution_from_chalk(
     solution: chalk_solve::Solution<Interner>,
 ) -> Solution {
     let convert_subst = |subst: chalk_ir::Canonical<chalk_ir::Substitution<Interner>>| {
-        let value = subst
-            .value
-            .iter(&Interner)
-            .map(|p| match p.ty(&Interner) {
-                Some(ty) => from_chalk(db, ty.clone()),
-                None => unimplemented!(),
-            })
-            .collect();
-        let result = Canonical { value, num_vars: subst.binders.len(&Interner) };
+        let result = from_chalk(db, subst);
         SolutionVariables(result)
     };
     match solution {
@@ -222,7 +214,7 @@ fn solution_from_chalk(
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub struct SolutionVariables(pub Canonical<Vec<Ty>>);
+pub struct SolutionVariables(pub Canonical<Substs>);
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 /// A (possible) solution for a proposed goal.
diff --git a/crates/ra_hir_ty/src/traits/chalk/mapping.rs b/crates/ra_hir_ty/src/traits/chalk/mapping.rs
index ac82ea831..433d6aa03 100644
--- a/crates/ra_hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/ra_hir_ty/src/traits/chalk/mapping.rs
@@ -17,7 +17,7 @@ use crate::{
     primitive::{FloatBitness, FloatTy, IntBitness, IntTy, Signedness},
     traits::{builtin, AssocTyValue, Canonical, Impl, Obligation},
     ApplicationTy, CallableDef, GenericPredicate, InEnvironment, OpaqueTy, OpaqueTyId,
-    ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TypeCtor,
+    ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeCtor,
 };
 
 use super::interner::*;
@@ -555,22 +555,39 @@ where
     type Chalk = chalk_ir::Canonical<T::Chalk>;
 
     fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Canonical<T::Chalk> {
-        let parameter = chalk_ir::CanonicalVarKind::new(
-            chalk_ir::VariableKind::Ty(chalk_ir::TyKind::General),
-            chalk_ir::UniverseIndex::ROOT,
-        );
+        let kinds = self
+            .kinds
+            .iter()
+            .map(|k| match k {
+                TyKind::General => chalk_ir::TyKind::General,
+                TyKind::Integer => chalk_ir::TyKind::Integer,
+                TyKind::Float => chalk_ir::TyKind::Float,
+            })
+            .map(|tk| {
+                chalk_ir::CanonicalVarKind::new(
+                    chalk_ir::VariableKind::Ty(tk),
+                    chalk_ir::UniverseIndex::ROOT,
+                )
+            });
         let value = self.value.to_chalk(db);
-        chalk_ir::Canonical {
-            value,
-            binders: chalk_ir::CanonicalVarKinds::from(&Interner, vec![parameter; self.num_vars]),
-        }
+        chalk_ir::Canonical { value, binders: chalk_ir::CanonicalVarKinds::from(&Interner, kinds) }
     }
 
     fn from_chalk(db: &dyn HirDatabase, canonical: chalk_ir::Canonical<T::Chalk>) -> Canonical<T> {
-        Canonical {
-            num_vars: canonical.binders.len(&Interner),
-            value: from_chalk(db, canonical.value),
-        }
+        let kinds = canonical
+            .binders
+            .iter(&Interner)
+            .map(|k| match k.kind {
+                chalk_ir::VariableKind::Ty(tk) => match tk {
+                    chalk_ir::TyKind::General => TyKind::General,
+                    chalk_ir::TyKind::Integer => TyKind::Integer,
+                    chalk_ir::TyKind::Float => TyKind::Float,
+                },
+                chalk_ir::VariableKind::Lifetime => panic!("unexpected lifetime from Chalk"),
+                chalk_ir::VariableKind::Const(_) => panic!("unexpected const from Chalk"),
+            })
+            .collect();
+        Canonical { kinds, value: from_chalk(db, canonical.value) }
     }
 }