Merge #1721 #1723

1721: Impl/dyn trait r=flodiebold a=flodiebold

This adds support for `impl Trait` and `dyn Trait` types as far as possible without Chalk. So we can represent them in the type system, and handle them in method resolution, but Chalk doesn't know about them yet. There's a small temporary hack here where we bypass Chalk during method resolution, so we can handle simple method calls on them and completion works.

Fixes #1608.

1723: Make sysroot use `RUST_SRC_PATH` if set r=matklad a=bkchr



Co-authored-by: Florian Diebold <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>

Author: 3 people

crates/ra_hir/src/generics.rs

@@ -11,7 +11,7 @@ use crate::{
     db::{AstDatabase, DefDatabase, HirDatabase},
     name::SELF_TYPE,
     path::Path,
-    type_ref::TypeRef,
+    type_ref::{TypeBound, TypeRef},
     AdtDef, AsName, Container, Enum, EnumVariant, Function, HasSource, ImplBlock, Name, Struct,
     Trait, TypeAlias, Union,
 };
@@ -35,10 +35,12 @@ pub struct GenericParams {
 
 /// A single predicate from a where clause, i.e. `where Type: Trait`. Combined
 /// where clauses like `where T: Foo + Bar` are turned into multiple of these.
+/// It might still result in multiple actual predicates though, because of
+/// associated type bindings like `Iterator<Item = u32>`.
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct WherePredicate {
     pub(crate) type_ref: TypeRef,
-    pub(crate) trait_ref: Path,
+    pub(crate) bound: TypeBound,
 }
 
 // FIXME: consts can have type parameters from their parents (i.e. associated consts of traits)
@@ -143,18 +145,8 @@ impl GenericParams {
             // FIXME: remove this bound
             return;
         }
-        let path = bound
-            .type_ref()
-            .and_then(|tr| match tr {
-                ast::TypeRef::PathType(path) => path.path(),
-                _ => None,
-            })
-            .and_then(Path::from_ast);
-        let path = match path {
-            Some(p) => p,
-            None => return,
-        };
-        self.where_predicates.push(WherePredicate { type_ref, trait_ref: path });
+        let bound = TypeBound::from_ast(bound);
+        self.where_predicates.push(WherePredicate { type_ref, bound });
     }
 
     pub(crate) fn find_by_name(&self, name: &Name) -> Option<&GenericParam> {

crates/ra_hir/src/ty.rs

@@ -161,14 +161,28 @@ pub enum Ty {
         name: Name,
     },
 
-    /// A bound type variable. Only used during trait resolution to represent
-    /// Chalk variables.
+    /// A bound type variable. Used during trait resolution to represent Chalk
+    /// variables, and in `Dyn` and `Opaque` bounds to represent the `Self` type.
     Bound(u32),
 
     /// A type variable used during type checking. Not to be confused with a
     /// type parameter.
     Infer(InferTy),
 
+    /// A trait object (`dyn Trait` or bare `Trait` in pre-2018 Rust).
+    ///
+    /// The predicates are quantified over the `Self` type, i.e. `Ty::Bound(0)`
+    /// represents the `Self` type inside the bounds. This is currently
+    /// implicit; Chalk has the `Binders` struct to make it explicit, but it
+    /// didn't seem worth the overhead yet.
+    Dyn(Arc<[GenericPredicate]>),
+
+    /// An opaque type (`impl Trait`).
+    ///
+    /// The predicates are quantified over the `Self` type; see `Ty::Dyn` for
+    /// more.
+    Opaque(Arc<[GenericPredicate]>),
+
     /// A placeholder for a type which could not be computed; this is propagated
     /// to avoid useless error messages. Doubles as a placeholder where type
     /// variables are inserted before type checking, since we want to try to
@@ -194,6 +208,12 @@ impl Substs {
         Substs(self.0.iter().cloned().take(n).collect::<Vec<_>>().into())
     }
 
+    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+        for t in self.0.iter() {
+            t.walk(f);
+        }
+    }
+
     pub 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.0.iter().cloned().collect();
@@ -270,6 +290,14 @@ impl TraitRef {
         });
         self
     }
+
+    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+        self.substs.walk(f);
+    }
+
+    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+        self.substs.walk_mut(f);
+    }
 }
 
 /// Like `generics::WherePredicate`, but with resolved types: A condition on the
@@ -299,6 +327,20 @@ impl GenericPredicate {
             GenericPredicate::Error => self,
         }
     }
+
+    pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
+        match self {
+            GenericPredicate::Implemented(trait_ref) => trait_ref.walk(f),
+            GenericPredicate::Error => {}
+        }
+    }
+
+    pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
+        match self {
+            GenericPredicate::Implemented(trait_ref) => trait_ref.walk_mut(f),
+            GenericPredicate::Error => {}
+        }
+    }
 }
 
 /// Basically a claim (currently not validated / checked) that the contained
@@ -386,6 +428,11 @@ impl Ty {
                     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);
@@ -402,6 +449,13 @@ impl Ty {
             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);
@@ -529,6 +583,19 @@ impl Ty {
             ty => ty,
         })
     }
+
+    /// 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,
+        }
+    }
 }
 
 impl HirDisplay for &Ty {
@@ -669,21 +736,45 @@ impl HirDisplay for Ty {
             Ty::UnselectedProjection(p_ty) => p_ty.hir_fmt(f)?,
             Ty::Param { name, .. } => write!(f, "{}", name)?,
             Ty::Bound(idx) => write!(f, "?{}", idx)?,
+            Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
+                match self {
+                    Ty::Dyn(_) => write!(f, "dyn ")?,
+                    Ty::Opaque(_) => write!(f, "impl ")?,
+                    _ => unreachable!(),
+                };
+                // looping by hand here just to format the bounds in a slightly nicer way
+                let mut first = true;
+                for p in predicates.iter() {
+                    if !first {
+                        write!(f, " + ")?;
+                    }
+                    first = false;
+                    match p {
+                        // don't show the $0 self type
+                        GenericPredicate::Implemented(trait_ref) => {
+                            trait_ref.hir_fmt_ext(f, false)?
+                        }
+                        GenericPredicate::Error => p.hir_fmt(f)?,
+                    }
+                }
+            }
             Ty::Unknown => write!(f, "{{unknown}}")?,
             Ty::Infer(..) => write!(f, "_")?,
         }
         Ok(())
     }
 }
 
-impl HirDisplay for TraitRef {
-    fn hir_fmt(&self, f: &mut HirFormatter<impl HirDatabase>) -> fmt::Result {
-        write!(
-            f,
-            "{}: {}",
-            self.substs[0].display(f.db),
-            self.trait_.name(f.db).unwrap_or_else(Name::missing)
-        )?;
+impl TraitRef {
+    fn hir_fmt_ext(
+        &self,
+        f: &mut HirFormatter<impl HirDatabase>,
+        with_self_ty: bool,
+    ) -> fmt::Result {
+        if with_self_ty {
+            write!(f, "{}: ", self.substs[0].display(f.db),)?;
+        }
+        write!(f, "{}", self.trait_.name(f.db).unwrap_or_else(Name::missing))?;
         if self.substs.len() > 1 {
             write!(f, "<")?;
             f.write_joined(&self.substs[1..], ", ")?;
@@ -693,6 +784,28 @@ impl HirDisplay for TraitRef {
     }
 }
 
+impl HirDisplay for TraitRef {
+    fn hir_fmt(&self, f: &mut HirFormatter<impl HirDatabase>) -> fmt::Result {
+        self.hir_fmt_ext(f, true)
+    }
+}
+
+impl HirDisplay for &GenericPredicate {
+    fn hir_fmt(&self, f: &mut HirFormatter<impl HirDatabase>) -> fmt::Result {
+        HirDisplay::hir_fmt(*self, f)
+    }
+}
+
+impl HirDisplay for GenericPredicate {
+    fn hir_fmt(&self, f: &mut HirFormatter<impl HirDatabase>) -> fmt::Result {
+        match self {
+            GenericPredicate::Implemented(trait_ref) => trait_ref.hir_fmt(f)?,
+            GenericPredicate::Error => write!(f, "{{error}}")?,
+        }
+        Ok(())
+    }
+}
+
 impl HirDisplay for Obligation {
     fn hir_fmt(&self, f: &mut HirFormatter<impl HirDatabase>) -> fmt::Result {
         match self {

crates/ra_hir/src/ty/lower.rs

@@ -17,7 +17,7 @@ use crate::{
     path::{GenericArg, PathSegment},
     resolve::{Resolution, Resolver},
     ty::AdtDef,
-    type_ref::TypeRef,
+    type_ref::{TypeBound, TypeRef},
     BuiltinType, Const, Enum, EnumVariant, Function, HirDatabase, ModuleDef, Path, Static, Struct,
     StructField, Trait, TypeAlias, Union,
 };
@@ -58,6 +58,22 @@ impl Ty {
                 let sig = Substs(inner_tys.into());
                 Ty::apply(TypeCtor::FnPtr { num_args: sig.len() as u16 - 1 }, sig)
             }
+            TypeRef::DynTrait(bounds) => {
+                let self_ty = Ty::Bound(0);
+                let predicates = bounds
+                    .iter()
+                    .map(|b| GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone()))
+                    .collect::<Vec<_>>();
+                Ty::Dyn(predicates.into())
+            }
+            TypeRef::ImplTrait(bounds) => {
+                let self_ty = Ty::Bound(0);
+                let predicates = bounds
+                    .iter()
+                    .map(|b| GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone()))
+                    .collect::<Vec<_>>();
+                Ty::Opaque(predicates.into())
+            }
             TypeRef::Error => Ty::Unknown,
         }
     }
@@ -310,13 +326,46 @@ impl TraitRef {
         TraitRef { trait_, substs }
     }
 
-    pub(crate) fn for_where_predicate(
+    pub(crate) fn from_where_predicate(
         db: &impl HirDatabase,
         resolver: &Resolver,
         pred: &WherePredicate,
     ) -> Option<TraitRef> {
         let self_ty = Ty::from_hir(db, resolver, &pred.type_ref);
-        TraitRef::from_path(db, resolver, &pred.trait_ref, Some(self_ty))
+        TraitRef::from_type_bound(db, resolver, &pred.bound, self_ty)
+    }
+
+    pub(crate) fn from_type_bound(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        bound: &TypeBound,
+        self_ty: Ty,
+    ) -> Option<TraitRef> {
+        match bound {
+            TypeBound::Path(path) => TraitRef::from_path(db, resolver, path, Some(self_ty)),
+            TypeBound::Error => None,
+        }
+    }
+}
+
+impl GenericPredicate {
+    pub(crate) fn from_where_predicate(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        where_predicate: &WherePredicate,
+    ) -> GenericPredicate {
+        TraitRef::from_where_predicate(db, &resolver, where_predicate)
+            .map_or(GenericPredicate::Error, GenericPredicate::Implemented)
+    }
+
+    pub(crate) fn from_type_bound(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        bound: &TypeBound,
+        self_ty: Ty,
+    ) -> GenericPredicate {
+        TraitRef::from_type_bound(db, &resolver, bound, self_ty)
+            .map_or(GenericPredicate::Error, GenericPredicate::Implemented)
     }
 }
 
@@ -376,10 +425,7 @@ pub(crate) fn trait_env(
 ) -> Arc<super::TraitEnvironment> {
     let predicates = resolver
         .where_predicates_in_scope()
-        .map(|pred| {
-            TraitRef::for_where_predicate(db, &resolver, pred)
-                .map_or(GenericPredicate::Error, GenericPredicate::Implemented)
-        })
+        .map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
         .collect::<Vec<_>>();
 
     Arc::new(super::TraitEnvironment { predicates })
@@ -393,10 +439,7 @@ pub(crate) fn generic_predicates_query(
     let resolver = def.resolver(db);
     let predicates = resolver
         .where_predicates_in_scope()
-        .map(|pred| {
-            TraitRef::for_where_predicate(db, &resolver, pred)
-                .map_or(GenericPredicate::Error, GenericPredicate::Implemented)
-        })
+        .map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
         .collect::<Vec<_>>();
     predicates.into()
 }

crates/ra_hir/src/ty/method_resolution.rs

@@ -211,12 +211,19 @@ fn iterate_trait_method_candidates<T>(
     let krate = resolver.krate()?;
     // FIXME: maybe put the trait_env behind a query (need to figure out good input parameters for that)
     let env = lower::trait_env(db, resolver);
-    'traits: for t in resolver.traits_in_scope(db) {
+    // if ty is `impl Trait` or `dyn Trait`, the trait doesn't need to be in scope
+    let traits = ty.value.inherent_trait().into_iter().chain(resolver.traits_in_scope(db));
+    'traits: for t in traits {
         let data = t.trait_data(db);
+
+        // FIXME this is a bit of a hack, since Chalk should say the same thing
+        // anyway, but currently Chalk doesn't implement `dyn/impl Trait` yet
+        let inherently_implemented = ty.value.inherent_trait() == Some(t);
+
         // we'll be lazy about checking whether the type implements the
         // trait, but if we find out it doesn't, we'll skip the rest of the
         // iteration
-        let mut known_implemented = false;
+        let mut known_implemented = inherently_implemented;
         for item in data.items() {
             if let TraitItem::Function(m) = *item {
                 let data = m.data(db);
@@ -271,6 +278,11 @@ pub(crate) fn implements_trait(
     krate: Crate,
     trait_: Trait,
 ) -> bool {
+    if ty.value.inherent_trait() == Some(trait_) {
+        // FIXME this is a bit of a hack, since Chalk should say the same thing
+        // anyway, but currently Chalk doesn't implement `dyn/impl Trait` yet
+        return true;
+    }
     let env = lower::trait_env(db, resolver);
     let goal = generic_implements_goal(db, env.clone(), trait_, ty.clone());
     let solution = db.trait_solve(krate, goal);