Merge #1501

1501: Infer for loop variable r=flodiebold a=unrealhoang

My take on https://github.com/rust-analyzer/rust-analyzer/issues/1425

Co-authored-by: Unreal Hoang <[email protected]>

5 files changed, 170 insertions, 35 deletions

diff --git a/crates/ra_hir/src/name.rs b/crates/ra_hir/src/name.rs
index 06a2dbc76..b71590560 100644
--- a/crates/ra_hir/src/name.rs
+++ b/crates/ra_hir/src/name.rs
@@ -86,6 +86,11 @@ impl Name {
             "Self" => KnownName::SelfType,
             "self" => KnownName::SelfParam,
             "macro_rules" => KnownName::MacroRules,
+
+            "std" => KnownName::Std,
+            "iter" => KnownName::Iter,
+            "IntoIterator" => KnownName::IntoIterator,
+            "Item" => KnownName::Item,
             _ => return None,
         };
         Some(name)
@@ -157,6 +162,11 @@ pub(crate) enum KnownName {
     SelfParam,
 
     MacroRules,
+
+    Std,
+    Iter,
+    IntoIterator,
+    Item,
 }
 
 impl AsName for KnownName {
@@ -182,6 +192,10 @@ impl AsName for KnownName {
             KnownName::SelfType => "Self",
             KnownName::SelfParam => "self",
             KnownName::MacroRules => "macro_rules",
+            KnownName::Std => "std",
+            KnownName::Iter => "iter",
+            KnownName::IntoIterator => "IntoIterator",
+            KnownName::Item => "Item",
         };
         Name::new(s.into())
     }
diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index e79e5e223..973de70df 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -28,24 +28,28 @@ use test_utils::tested_by;
 
 use super::{
     autoderef, method_resolution, op, primitive,
-    traits::{Guidance, Obligation, Solution},
-    ApplicationTy, CallableDef, Substs, TraitRef, Ty, TypableDef, TypeCtor,
+    traits::{Guidance, Obligation, ProjectionPredicate, Solution},
+    ApplicationTy, CallableDef, ProjectionTy, Substs, TraitRef, Ty, TypableDef, TypeCtor,
 };
 use crate::{
     adt::VariantDef,
+    code_model::{ModuleDef::Trait, TypeAlias},
     diagnostics::DiagnosticSink,
     expr::{
         self, Array, BinaryOp, BindingAnnotation, Body, Expr, ExprId, FieldPat, Literal, Pat,
         PatId, Statement, UnaryOp,
     },
     generics::{GenericParams, HasGenericParams},
-    nameres::Namespace,
-    path::{GenericArg, GenericArgs},
-    resolve::{Resolution, Resolver},
+    nameres::{Namespace, PerNs},
+    path::{GenericArg, GenericArgs, PathKind, PathSegment},
+    resolve::{
+        Resolution::{self, Def},
+        Resolver,
+    },
     ty::infer::diagnostics::InferenceDiagnostic,
     type_ref::{Mutability, TypeRef},
-    AdtDef, ConstData, DefWithBody, FnData, Function, HirDatabase, ImplItem, ModuleDef, Name, Path,
-    StructField,
+    AdtDef, AsName, ConstData, DefWithBody, FnData, Function, HirDatabase, ImplItem, KnownName,
+    ModuleDef, Name, Path, StructField,
 };
 
 mod unify;
@@ -323,34 +327,53 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn resolve_obligations_as_possible(&mut self) {
         let obligations = mem::replace(&mut self.obligations, Vec::new());
         for obligation in obligations {
-            let (solution, canonicalized) = match &obligation {
+            match &obligation {
                 Obligation::Trait(tr) => {
                     let canonicalized = self.canonicalizer().canonicalize_trait_ref(tr.clone());
-                    (
-                        self.db.implements(
-                            self.resolver.krate().unwrap(),
-                            canonicalized.value.clone(),
-                        ),
-                        canonicalized,
-                    )
-                }
-            };
-            match solution {
-                Some(Solution::Unique(substs)) => {
-                    canonicalized.apply_solution(self, substs.0);
-                }
-                Some(Solution::Ambig(Guidance::Definite(substs))) => {
-                    canonicalized.apply_solution(self, substs.0);
-                    self.obligations.push(obligation);
-                }
-                Some(_) => {
-                    // FIXME use this when trying to resolve everything at the end
-                    self.obligations.push(obligation);
+                    let solution = self
+                        .db
+                        .implements(self.resolver.krate().unwrap(), canonicalized.value.clone());
+                    match solution {
+                        Some(Solution::Unique(substs)) => {
+                            canonicalized.apply_solution(self, substs.0);
+                        }
+                        Some(Solution::Ambig(Guidance::Definite(substs))) => {
+                            canonicalized.apply_solution(self, substs.0);
+                            self.obligations.push(obligation);
+                        }
+                        Some(_) => {
+                            // FIXME use this when trying to resolve everything at the end
+                            self.obligations.push(obligation);
+                        }
+                        None => {
+                            // FIXME obligation cannot be fulfilled => diagnostic
+                        }
+                    };
                 }
-                None => {
-                    // FIXME obligation cannot be fulfilled => diagnostic
+                Obligation::Projection(pr) => {
+                    let canonicalized = self.canonicalizer().canonicalize_projection(pr.clone());
+                    let solution = self
+                        .db
+                        .normalize(self.resolver.krate().unwrap(), canonicalized.value.clone());
+
+                    match solution {
+                        Some(Solution::Unique(substs)) => {
+                            canonicalized.apply_solution(self, substs.0);
+                        }
+                        Some(Solution::Ambig(Guidance::Definite(substs))) => {
+                            canonicalized.apply_solution(self, substs.0);
+                            self.obligations.push(obligation);
+                        }
+                        Some(_) => {
+                            // FIXME use this when trying to resolve everything at the end
+                            self.obligations.push(obligation);
+                        }
+                        None => {
+                            // FIXME obligation cannot be fulfilled => diagnostic
+                        }
+                    };
                 }
-            }
+            };
         }
     }
 
@@ -967,8 +990,25 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 Ty::unit()
             }
             Expr::For { iterable, body, pat } => {
-                let _iterable_ty = self.infer_expr(*iterable, &Expectation::none());
-                self.infer_pat(*pat, &Ty::Unknown, BindingMode::default());
+                let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
+
+                let pat_ty = match self.resolve_into_iter_item() {
+                    Some(into_iter_item_alias) => {
+                        let pat_ty = self.new_type_var();
+                        let projection = ProjectionPredicate {
+                            ty: pat_ty.clone(),
+                            projection_ty: ProjectionTy {
+                                associated_ty: into_iter_item_alias,
+                                parameters: vec![iterable_ty].into(),
+                            },
+                        };
+                        self.obligations.push(Obligation::Projection(projection));
+                        self.resolve_ty_as_possible(&mut vec![], pat_ty)
+                    }
+                    None => Ty::Unknown,
+                };
+
+                self.infer_pat(*pat, &pat_ty, BindingMode::default());
                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
                 Ty::unit()
             }
@@ -1301,6 +1341,24 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn infer_body(&mut self) {
         self.infer_expr(self.body.body_expr(), &Expectation::has_type(self.return_ty.clone()));
     }
+
+    fn resolve_into_iter_item(&self) -> Option<TypeAlias> {
+        let into_iter_path = Path {
+            kind: PathKind::Abs,
+            segments: vec![
+                PathSegment { name: KnownName::Std.as_name(), args_and_bindings: None },
+                PathSegment { name: KnownName::Iter.as_name(), args_and_bindings: None },
+                PathSegment { name: KnownName::IntoIterator.as_name(), args_and_bindings: None },
+            ],
+        };
+
+        match self.resolver.resolve_path_segments(self.db, &into_iter_path).into_fully_resolved() {
+            PerNs { types: Some(Def(Trait(trait_))), .. } => {
+                Some(trait_.associated_type_by_name(self.db, KnownName::Item.as_name())?)
+            }
+            _ => None,
+        }
+    }
 }
 
 /// The ID of a type variable.
diff --git a/crates/ra_hir/src/ty/infer/unify.rs b/crates/ra_hir/src/ty/infer/unify.rs
index 49bf5b946..a24e5eb5c 100644
--- a/crates/ra_hir/src/ty/infer/unify.rs
+++ b/crates/ra_hir/src/ty/infer/unify.rs
@@ -2,7 +2,7 @@
 
 use super::InferenceContext;
 use crate::db::HirDatabase;
-use crate::ty::{Canonical, InferTy, TraitRef, Ty};
+use crate::ty::{Canonical, InferTy, ProjectionPredicate, ProjectionTy, TraitRef, Ty};
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     pub(super) fn canonicalizer<'b>(&'b mut self) -> Canonicalizer<'a, 'b, D>
@@ -86,6 +86,25 @@ where
         }
     }
 
+    fn do_canonicalize_projection_ty(&mut self, projection_ty: ProjectionTy) -> ProjectionTy {
+        let params = projection_ty
+            .parameters
+            .iter()
+            .map(|ty| self.do_canonicalize_ty(ty.clone()))
+            .collect::<Vec<_>>();
+        ProjectionTy { associated_ty: projection_ty.associated_ty, parameters: params.into() }
+    }
+
+    fn do_canonicalize_projection_predicate(
+        &mut self,
+        projection: ProjectionPredicate,
+    ) -> ProjectionPredicate {
+        let ty = self.do_canonicalize_ty(projection.ty);
+        let projection_ty = self.do_canonicalize_projection_ty(projection.projection_ty);
+
+        ProjectionPredicate { ty, projection_ty }
+    }
+
     pub fn canonicalize_ty(mut self, ty: Ty) -> Canonicalized<Ty> {
         let result = self.do_canonicalize_ty(ty);
         self.into_canonicalized(result)
@@ -95,6 +114,14 @@ where
         let result = self.do_canonicalize_trait_ref(trait_ref);
         self.into_canonicalized(result)
     }
+
+    pub fn canonicalize_projection(
+        mut self,
+        projection: ProjectionPredicate,
+    ) -> Canonicalized<ProjectionPredicate> {
+        let result = self.do_canonicalize_projection_predicate(projection);
+        self.into_canonicalized(result)
+    }
 }
 
 impl<T> Canonicalized<T> {
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index aacd94a26..fe5e89f2d 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -21,6 +21,42 @@ use crate::{
 // update the snapshots.
 
 #[test]
+fn infer_for_loop() {
+    let (mut db, pos) = MockDatabase::with_position(
+        r#"
+//- /main.rs
+struct Vec<T> {}
+impl<T> Vec<T> {
+    fn new() -> Self { Vec {} }
+    fn push(&mut self, t: T) { }
+}
+
+impl<T> ::std::iter::IntoIterator for Vec<T> {
+    type Item=T;
+}
+fn test() {
+    let v = Vec::new();
+    v.push("foo");
+    for x in v {
+        x<|>;
+    }
+}
+
+//- /lib.rs
+mod iter {
+    trait IntoIterator {
+        type Item;
+    }
+}
+"#,
+    );
+    db.set_crate_graph_from_fixture(crate_graph! {
+        "main": ("/main.rs", ["std"]),
+        "std": ("/lib.rs", []),
+    });
+    assert_eq!("&str", type_at_pos(&db, pos));
+}
+#[test]
 fn infer_basics() {
     assert_snapshot_matches!(
         infer(r#"
diff --git a/crates/ra_hir/src/ty/traits.rs b/crates/ra_hir/src/ty/traits.rs
index 23a26a971..3e28852b6 100644
--- a/crates/ra_hir/src/ty/traits.rs
+++ b/crates/ra_hir/src/ty/traits.rs
@@ -75,7 +75,7 @@ pub enum Obligation {
     /// Prove that a certain type implements a trait (the type is the `Self` type
     /// parameter to the `TraitRef`).
     Trait(TraitRef),
-    // Projection(ProjectionPredicate),
+    Projection(ProjectionPredicate),
 }
 
 impl Obligation {