Make type walking infrastructure a bit nicer

If/when we switch to using Chalk's Ty, we'll need to replace this by its `Fold`
trait, but I didn't want to import the whole thing just yet.

10 files changed, 134 insertions, 135 deletions

diff --git a/crates/ra_cli/src/analysis_stats.rs b/crates/ra_cli/src/analysis_stats.rs
index 5c0a9dd98..1fad5b233 100644
--- a/crates/ra_cli/src/analysis_stats.rs
+++ b/crates/ra_cli/src/analysis_stats.rs
@@ -1,7 +1,7 @@
 use std::{collections::HashSet, fmt::Write, path::Path, time::Instant};
 
 use ra_db::SourceDatabase;
-use ra_hir::{Crate, HasBodySource, HasSource, HirDisplay, ImplItem, ModuleDef, Ty};
+use ra_hir::{Crate, HasBodySource, HasSource, HirDisplay, ImplItem, ModuleDef, Ty, TypeWalk};
 use ra_syntax::AstNode;
 
 use crate::Result;
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index 752653ad7..c3e589921 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -69,7 +69,9 @@ pub use self::{
     resolve::Resolution,
     source_binder::{PathResolution, ScopeEntryWithSyntax, SourceAnalyzer},
     source_id::{AstIdMap, ErasedFileAstId},
-    ty::{display::HirDisplay, ApplicationTy, CallableDef, Substs, TraitRef, Ty, TypeCtor},
+    ty::{
+        display::HirDisplay, ApplicationTy, CallableDef, Substs, TraitRef, Ty, TypeCtor, TypeWalk,
+    },
     type_ref::Mutability,
 };
 
diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index c0c609d78..a3df08827 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -130,12 +130,14 @@ impl ProjectionTy {
             substs: self.parameters.clone(),
         }
     }
+}
 
-    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+impl TypeWalk for ProjectionTy {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
         self.parameters.walk(f);
     }
 
-    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
         self.parameters.walk_mut(f);
     }
 }
@@ -146,12 +148,12 @@ pub struct UnselectedProjectionTy {
     pub parameters: Substs,
 }
 
-impl UnselectedProjectionTy {
-    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+impl TypeWalk for UnselectedProjectionTy {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
         self.parameters.walk(f);
     }
 
-    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
         self.parameters.walk_mut(f);
     }
 }
@@ -312,20 +314,14 @@ impl TraitRef {
     pub fn self_ty(&self) -> &Ty {
         &self.substs[0]
     }
+}
 
-    pub fn subst(mut self, substs: &Substs) -> TraitRef {
-        self.substs.walk_mut(&mut |ty_mut| {
-            let ty = mem::replace(ty_mut, Ty::Unknown);
-            *ty_mut = ty.subst(substs);
-        });
-        self
-    }
-
-    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+impl TypeWalk for TraitRef {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
         self.substs.walk(f);
     }
 
-    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
         self.substs.walk_mut(f);
     }
 }
@@ -365,20 +361,10 @@ impl GenericPredicate {
             GenericPredicate::Error => None,
         }
     }
+}
 
-    pub fn subst(self, substs: &Substs) -> GenericPredicate {
-        match self {
-            GenericPredicate::Implemented(trait_ref) => {
-                GenericPredicate::Implemented(trait_ref.subst(substs))
-            }
-            GenericPredicate::Projection(projection_predicate) => {
-                GenericPredicate::Projection(projection_predicate.subst(substs))
-            }
-            GenericPredicate::Error => self,
-        }
-    }
-
-    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+impl TypeWalk for GenericPredicate {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
         match self {
             GenericPredicate::Implemented(trait_ref) => trait_ref.walk(f),
             GenericPredicate::Projection(projection_pred) => projection_pred.walk(f),
@@ -386,7 +372,7 @@ impl GenericPredicate {
         }
     }
 
-    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
         match self {
             GenericPredicate::Implemented(trait_ref) => trait_ref.walk_mut(f),
             GenericPredicate::Projection(projection_pred) => projection_pred.walk_mut(f),
@@ -430,16 +416,16 @@ impl FnSig {
     pub fn ret(&self) -> &Ty {
         &self.params_and_return[self.params_and_return.len() - 1]
     }
+}
 
-    /// Applies the given substitutions to all types in this signature and
-    /// returns the result.
-    pub fn subst(&self, substs: &Substs) -> FnSig {
-        let result: Vec<_> =
-            self.params_and_return.iter().map(|ty| ty.clone().subst(substs)).collect();
-        FnSig { params_and_return: result.into() }
+impl TypeWalk for FnSig {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
+        for t in self.params_and_return.iter() {
+            t.walk(f);
+        }
     }
 
-    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
         // Without an Arc::make_mut_slice, we can't avoid the clone here:
         let mut v: Vec<_> = self.params_and_return.iter().cloned().collect();
         for t in &mut v {
@@ -463,64 +449,6 @@ impl Ty {
         Ty::apply(TypeCtor::Tuple { cardinality: 0 }, Substs::empty())
     }
 
-    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
-        match self {
-            Ty::Apply(a_ty) => {
-                for t in a_ty.parameters.iter() {
-                    t.walk(f);
-                }
-            }
-            Ty::Projection(p_ty) => {
-                for t in p_ty.parameters.iter() {
-                    t.walk(f);
-                }
-            }
-            Ty::UnselectedProjection(p_ty) => {
-                for t in p_ty.parameters.iter() {
-                    t.walk(f);
-                }
-            }
-            Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
-                for p in predicates.iter() {
-                    p.walk(f);
-                }
-            }
-            Ty::Param { .. } | Ty::Bound(_) | Ty::Infer(_) | Ty::Unknown => {}
-        }
-        f(self);
-    }
-
-    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
-        match self {
-            Ty::Apply(a_ty) => {
-                a_ty.parameters.walk_mut(f);
-            }
-            Ty::Projection(p_ty) => {
-                p_ty.parameters.walk_mut(f);
-            }
-            Ty::UnselectedProjection(p_ty) => {
-                p_ty.parameters.walk_mut(f);
-            }
-            Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
-                let mut v: Vec<_> = predicates.iter().cloned().collect();
-                for p in &mut v {
-                    p.walk_mut(f);
-                }
-                *predicates = v.into();
-            }
-            Ty::Param { .. } | Ty::Bound(_) | Ty::Infer(_) | Ty::Unknown => {}
-        }
-        f(self);
-    }
-
-    fn fold(mut self, f: &mut impl FnMut(Ty) -> Ty) -> Ty {
-        self.walk_mut(&mut |ty_mut| {
-            let ty = mem::replace(ty_mut, Ty::Unknown);
-            *ty_mut = f(ty);
-        });
-        self
-    }
-
     pub fn as_reference(&self) -> Option<(&Ty, Mutability)> {
         match self {
             Ty::Apply(ApplicationTy { ctor: TypeCtor::Ref(mutability), parameters }) => {
@@ -596,10 +524,53 @@ impl Ty {
         }
     }
 
+    /// Returns the type parameters of this type if it has some (i.e. is an ADT
+    /// or function); so if `self` is `Option<u32>`, this returns the `u32`.
+    pub fn substs(&self) -> Option<Substs> {
+        match self {
+            Ty::Apply(ApplicationTy { parameters, .. }) => Some(parameters.clone()),
+            _ => None,
+        }
+    }
+
+    /// If this is an `impl Trait` or `dyn Trait`, returns that trait.
+    pub fn inherent_trait(&self) -> Option<Trait> {
+        match self {
+            Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
+                predicates.iter().find_map(|pred| match pred {
+                    GenericPredicate::Implemented(tr) => Some(tr.trait_),
+                    _ => None,
+                })
+            }
+            _ => None,
+        }
+    }
+}
+
+/// This allows walking structures that contain types to do something with those
+/// types, similar to Chalk's `Fold` trait.
+pub trait TypeWalk {
+    fn walk(&self, f: &mut impl FnMut(&Ty));
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty));
+
+    fn fold(mut self, f: &mut impl FnMut(Ty) -> Ty) -> Self
+    where
+        Self: Sized,
+    {
+        self.walk_mut(&mut |ty_mut| {
+            let ty = mem::replace(ty_mut, Ty::Unknown);
+            *ty_mut = f(ty);
+        });
+        self
+    }
+
     /// Replaces type parameters in this type using the given `Substs`. (So e.g.
     /// if `self` is `&[T]`, where type parameter T has index 0, and the
     /// `Substs` contain `u32` at index 0, we'll have `&[u32]` afterwards.)
-    pub fn subst(self, substs: &Substs) -> Ty {
+    fn subst(self, substs: &Substs) -> Self
+    where
+        Self: Sized,
+    {
         self.fold(&mut |ty| match ty {
             Ty::Param { idx, name } => {
                 substs.get(idx as usize).cloned().unwrap_or(Ty::Param { idx, name })
@@ -609,24 +580,21 @@ impl Ty {
     }
 
     /// Substitutes `Ty::Bound` vars (as opposed to type parameters).
-    pub fn subst_bound_vars(self, substs: &Substs) -> Ty {
+    fn subst_bound_vars(self, substs: &Substs) -> Self
+    where
+        Self: Sized,
+    {
         self.fold(&mut |ty| match ty {
             Ty::Bound(idx) => substs.get(idx as usize).cloned().unwrap_or_else(|| Ty::Bound(idx)),
             ty => ty,
         })
     }
 
-    /// Returns the type parameters of this type if it has some (i.e. is an ADT
-    /// or function); so if `self` is `Option<u32>`, this returns the `u32`.
-    pub fn substs(&self) -> Option<Substs> {
-        match self {
-            Ty::Apply(ApplicationTy { parameters, .. }) => Some(parameters.clone()),
-            _ => None,
-        }
-    }
-
     /// Shifts up `Ty::Bound` vars by `n`.
-    pub fn shift_bound_vars(self, n: i32) -> Ty {
+    fn shift_bound_vars(self, n: i32) -> Self
+    where
+        Self: Sized,
+    {
         self.fold(&mut |ty| match ty {
             Ty::Bound(idx) => {
                 assert!(idx as i32 >= -n);
@@ -635,18 +603,57 @@ impl Ty {
             ty => ty,
         })
     }
+}
 
-    /// If this is an `impl Trait` or `dyn Trait`, returns that trait.
-    pub fn inherent_trait(&self) -> Option<Trait> {
+impl TypeWalk for Ty {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
         match self {
+            Ty::Apply(a_ty) => {
+                for t in a_ty.parameters.iter() {
+                    t.walk(f);
+                }
+            }
+            Ty::Projection(p_ty) => {
+                for t in p_ty.parameters.iter() {
+                    t.walk(f);
+                }
+            }
+            Ty::UnselectedProjection(p_ty) => {
+                for t in p_ty.parameters.iter() {
+                    t.walk(f);
+                }
+            }
             Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
-                predicates.iter().find_map(|pred| match pred {
-                    GenericPredicate::Implemented(tr) => Some(tr.trait_),
-                    _ => None,
-                })
+                for p in predicates.iter() {
+                    p.walk(f);
+                }
             }
-            _ => None,
+            Ty::Param { .. } | Ty::Bound(_) | Ty::Infer(_) | Ty::Unknown => {}
+        }
+        f(self);
+    }
+
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+        match self {
+            Ty::Apply(a_ty) => {
+                a_ty.parameters.walk_mut(f);
+            }
+            Ty::Projection(p_ty) => {
+                p_ty.parameters.walk_mut(f);
+            }
+            Ty::UnselectedProjection(p_ty) => {
+                p_ty.parameters.walk_mut(f);
+            }
+            Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
+                let mut v: Vec<_> = predicates.iter().cloned().collect();
+                for p in &mut v {
+                    p.walk_mut(f);
+                }
+                *predicates = v.into();
+            }
+            Ty::Param { .. } | Ty::Bound(_) | Ty::Infer(_) | Ty::Unknown => {}
         }
+        f(self);
     }
 }
 
diff --git a/crates/ra_hir/src/ty/autoderef.rs b/crates/ra_hir/src/ty/autoderef.rs
index 2535d4ae7..08f52a53b 100644
--- a/crates/ra_hir/src/ty/autoderef.rs
+++ b/crates/ra_hir/src/ty/autoderef.rs
@@ -7,7 +7,7 @@ use std::iter::successors;
 
 use log::{info, warn};
 
-use super::{traits::Solution, Canonical, Ty};
+use super::{traits::Solution, Canonical, Ty, TypeWalk};
 use crate::{HasGenericParams, HirDatabase, Name, Resolver};
 
 const AUTODEREF_RECURSION_LIMIT: usize = 10;
diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index b89a40b4b..ec3b7ffef 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -30,7 +30,7 @@ use super::{
     autoderef, lower, method_resolution, op, primitive,
     traits::{Guidance, Obligation, ProjectionPredicate, Solution},
     ApplicationTy, CallableDef, InEnvironment, ProjectionTy, Substs, TraitEnvironment, TraitRef,
-    Ty, TypableDef, TypeCtor,
+    Ty, TypableDef, TypeCtor, TypeWalk,
 };
 use crate::{
     adt::VariantDef,
diff --git a/crates/ra_hir/src/ty/infer/unify.rs b/crates/ra_hir/src/ty/infer/unify.rs
index e7e8825d1..9a0d2d8f9 100644
--- a/crates/ra_hir/src/ty/infer/unify.rs
+++ b/crates/ra_hir/src/ty/infer/unify.rs
@@ -3,7 +3,7 @@
 use super::{InferenceContext, Obligation};
 use crate::db::HirDatabase;
 use crate::ty::{
-    Canonical, InEnvironment, InferTy, ProjectionPredicate, ProjectionTy, TraitRef, Ty,
+    Canonical, InEnvironment, InferTy, ProjectionPredicate, ProjectionTy, TraitRef, Ty, TypeWalk,
 };
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
diff --git a/crates/ra_hir/src/ty/lower.rs b/crates/ra_hir/src/ty/lower.rs
index 0011c06b4..f6f0137cf 100644
--- a/crates/ra_hir/src/ty/lower.rs
+++ b/crates/ra_hir/src/ty/lower.rs
@@ -10,6 +10,7 @@ use std::sync::Arc;
 
 use super::{
     FnSig, GenericPredicate, ProjectionPredicate, ProjectionTy, Substs, TraitRef, Ty, TypeCtor,
+    TypeWalk,
 };
 use crate::{
     adt::VariantDef,
diff --git a/crates/ra_hir/src/ty/traits.rs b/crates/ra_hir/src/ty/traits.rs
index 25316bc02..6e0271a96 100644
--- a/crates/ra_hir/src/ty/traits.rs
+++ b/crates/ra_hir/src/ty/traits.rs
@@ -8,7 +8,7 @@ use ra_db::salsa;
 use ra_prof::profile;
 use rustc_hash::FxHashSet;
 
-use super::{Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty};
+use super::{Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty, TypeWalk};
 use crate::{db::HirDatabase, Crate, ImplBlock, Trait};
 
 use self::chalk::{from_chalk, ToChalk};
@@ -138,25 +138,13 @@ pub struct ProjectionPredicate {
     pub ty: Ty,
 }
 
-impl ProjectionPredicate {
-    pub fn subst(mut self, substs: &super::Substs) -> ProjectionPredicate {
-        self.walk_mut(&mut |ty| match ty {
-            Ty::Param { idx, .. } => {
-                if let Some(t) = substs.get(*idx as usize).cloned() {
-                    *ty = t;
-                }
-            }
-            _ => {}
-        });
-        self
-    }
-
-    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+impl TypeWalk for ProjectionPredicate {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
         self.projection_ty.walk(f);
         self.ty.walk(f);
     }
 
-    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
         self.projection_ty.walk_mut(f);
         self.ty.walk_mut(f);
     }
diff --git a/crates/ra_hir/src/ty/traits/chalk.rs b/crates/ra_hir/src/ty/traits/chalk.rs
index 3ab5b7cca..c201c5e50 100644
--- a/crates/ra_hir/src/ty/traits/chalk.rs
+++ b/crates/ra_hir/src/ty/traits/chalk.rs
@@ -19,6 +19,7 @@ use crate::{
     ty::display::HirDisplay,
     ty::{
         ApplicationTy, CallableDef, GenericPredicate, ProjectionTy, Substs, TraitRef, Ty, TypeCtor,
+        TypeWalk,
     },
     Crate, HasGenericParams, ImplBlock, ImplItem, Trait, TypeAlias,
 };
diff --git a/crates/ra_ide_api/src/completion/presentation.rs b/crates/ra_ide_api/src/completion/presentation.rs
index f19eec9b7..db7e8348e 100644
--- a/crates/ra_ide_api/src/completion/presentation.rs
+++ b/crates/ra_ide_api/src/completion/presentation.rs
@@ -1,5 +1,5 @@
 //! This modules takes care of rendering various defenitions as completion items.
-use hir::{Docs, HasSource, HirDisplay, PerNs, Resolution, Ty};
+use hir::{Docs, HasSource, HirDisplay, PerNs, Resolution, Ty, TypeWalk};
 use join_to_string::join;
 use ra_syntax::ast::NameOwner;
 use test_utils::tested_by;