From 6d8903ae5f3d3a16a96e0a3e3f32ce88d7998392 Mon Sep 17 00:00:00 2001
From: Ryo Yoshida <low.ryoshida@gmail.com>
Date: Thu, 29 Sep 2022 18:44:45 +0900
Subject: [PATCH] fix: infer for-loop item type with `IntoIterator` and
 `Iterator`

---
 crates/hir-expand/src/name.rs     |  1 +
 crates/hir-ty/src/infer.rs        |  6 ++++++
 crates/hir-ty/src/infer/expr.rs   |  4 +++-
 crates/hir-ty/src/tests/traits.rs | 12 +++++++++++-
 crates/ide/src/inlay_hints.rs     |  9 ++++++++-
 5 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/crates/hir-expand/src/name.rs b/crates/hir-expand/src/name.rs
index 4ce21a57967..2679a1c3602 100644
--- a/crates/hir-expand/src/name.rs
+++ b/crates/hir-expand/src/name.rs
@@ -263,6 +263,7 @@ macro_rules! known_names {
         Iterator,
         IntoIterator,
         Item,
+        IntoIter,
         Try,
         Ok,
         Future,
diff --git a/crates/hir-ty/src/infer.rs b/crates/hir-ty/src/infer.rs
index 039824694ac..25179afaca7 100644
--- a/crates/hir-ty/src/infer.rs
+++ b/crates/hir-ty/src/infer.rs
@@ -883,6 +883,12 @@ fn resolve_lang_item(&self, name: Name) -> Option<LangItemTarget> {
     fn resolve_into_iter_item(&self) -> Option<TypeAliasId> {
         let path = path![core::iter::IntoIterator];
         let trait_ = self.resolver.resolve_known_trait(self.db.upcast(), &path)?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![IntoIter])
+    }
+
+    fn resolve_iterator_item(&self) -> Option<TypeAliasId> {
+        let path = path![core::iter::Iterator];
+        let trait_ = self.resolver.resolve_known_trait(self.db.upcast(), &path)?;
         self.db.trait_data(trait_).associated_type_by_name(&name![Item])
     }
 
diff --git a/crates/hir-ty/src/infer/expr.rs b/crates/hir-ty/src/infer/expr.rs
index e3d6be23e65..2643baf8a32 100644
--- a/crates/hir-ty/src/infer/expr.rs
+++ b/crates/hir-ty/src/infer/expr.rs
@@ -207,8 +207,10 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
             }
             &Expr::For { iterable, body, pat, label } => {
                 let iterable_ty = self.infer_expr(iterable, &Expectation::none());
-                let pat_ty =
+                let into_iter_ty =
                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
+                let pat_ty =
+                    self.resolve_associated_type(into_iter_ty, self.resolve_iterator_item());
 
                 self.infer_pat(pat, &pat_ty, BindingMode::default());
                 self.with_breakable_ctx(BreakableKind::Loop, self.err_ty(), label, |this| {
diff --git a/crates/hir-ty/src/tests/traits.rs b/crates/hir-ty/src/tests/traits.rs
index 21a86319763..555b6972fb7 100644
--- a/crates/hir-ty/src/tests/traits.rs
+++ b/crates/hir-ty/src/tests/traits.rs
@@ -279,6 +279,10 @@ fn test() {
 pub mod iter {
     pub trait IntoIterator {
         type Item;
+        type IntoIter: Iterator<Item = Self::Item>;
+    }
+    pub trait Iterator {
+        type Item;
     }
 }
 pub mod prelude {
@@ -297,7 +301,13 @@ pub fn push(&mut self, t: T) { }
     }
 
     impl<T> IntoIterator for Vec<T> {
-        type Item=T;
+        type Item = T;
+        type IntoIter = IntoIter<T>;
+    }
+
+    struct IntoIter<T> {}
+    impl<T> Iterator for IntoIter<T> {
+        type Item = T;
     }
 }
 "#,
diff --git a/crates/ide/src/inlay_hints.rs b/crates/ide/src/inlay_hints.rs
index 08363d21e89..34d8bf67a30 100644
--- a/crates/ide/src/inlay_hints.rs
+++ b/crates/ide/src/inlay_hints.rs
@@ -2024,7 +2024,14 @@ pub fn push(&mut self, t: T) {}
 }
 
 impl<T> IntoIterator for Vec<T> {
-    type Item=T;
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+}
+
+struct IntoIter<T> {}
+
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
 }
 
 fn main() {