3 files changed, 125 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index f6283ab6d..fe259371f 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -577,6 +577,42 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
         Some(struct_.into())
     }
+
+    fn resolve_range_full(&self) -> Option<AdtId> {
+        let path = known::std_ops_range_full();
+        let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range(&self) -> Option<AdtId> {
+        let path = known::std_ops_range();
+        let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_inclusive(&self) -> Option<AdtId> {
+        let path = known::std_ops_range_inclusive();
+        let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_from(&self) -> Option<AdtId> {
+        let path = known::std_ops_range_from();
+        let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_to(&self) -> Option<AdtId> {
+        let path = known::std_ops_range_to();
+        let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_to_inclusive(&self) -> Option<AdtId> {
+        let path = known::std_ops_range_to_inclusive();
+        let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
+        Some(struct_.into())
+    }
 }
 
 /// The ID of a type variable.
diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index 2f9ca4bbb..4014f4732 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -12,6 +12,7 @@ use hir_def::{
     AdtId, ContainerId, Lookup, StructFieldId,
 };
 use hir_expand::name::{self, Name};
+use ra_syntax::ast::RangeOp;
 
 use crate::{
     autoderef, db::HirDatabase, method_resolution, op, traits::InEnvironment, utils::variant_data,
@@ -415,6 +416,44 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 }
                 _ => Ty::Unknown,
             },
+            Expr::Range { lhs, rhs, range_type } => {
+                let lhs_ty = lhs.map(|e| self.infer_expr(e, &Expectation::none()));
+                let rhs_expect = lhs_ty
+                    .as_ref()
+                    .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
+                let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
+                match (range_type, lhs_ty, rhs_ty) {
+                    (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
+                        Some(adt) => Ty::simple(TypeCtor::Adt(adt)),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
+                        Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Inclusive, None, Some(ty)) => {
+                        match self.resolve_range_to_inclusive() {
+                            Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                            None => Ty::Unknown,
+                        }
+                    }
+                    (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
+                        Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Inclusive, Some(_), Some(ty)) => {
+                        match self.resolve_range_inclusive() {
+                            Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                            None => Ty::Unknown,
+                        }
+                    }
+                    (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
+                        Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Inclusive, _, None) => Ty::Unknown,
+                }
+            }
             Expr::Index { base, index } => {
                 let _base_ty = self.infer_expr(*base, &Expectation::none());
                 let _index_ty = self.infer_expr(*index, &Expectation::none());
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index abbc1546c..4ba87e667 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/crates/ra_hir_ty/src/tests.rs
@@ -222,6 +222,56 @@ mod collections {
 }
 
 #[test]
+fn infer_ranges() {
+    let (db, pos) = TestDB::with_position(
+        r#"
+//- /main.rs crate:main deps:std
+fn test() {
+    let a = ..;
+    let b = 1..;
+    let c = ..2u32;
+    let d = 1..2usize;
+    let e = ..=10;
+    let f = 'a'..='z';
+
+    let t = (a, b, c, d, e, f);
+    t<|>;
+}
+
+//- /std.rs crate:std
+#[prelude_import] use prelude::*;
+mod prelude {}
+
+pub mod ops {
+    pub struct Range<Idx> {
+        pub start: Idx,
+        pub end: Idx,
+    }
+    pub struct RangeFrom<Idx> {
+        pub start: Idx,
+    }
+    struct RangeFull;
+    pub struct RangeInclusive<Idx> {
+        start: Idx,
+        end: Idx,
+        is_empty: u8,
+    }
+    pub struct RangeTo<Idx> {
+        pub end: Idx,
+    }
+    pub struct RangeToInclusive<Idx> {
+        pub end: Idx,
+    }
+}
+"#,
+    );
+    assert_eq!(
+        "(RangeFull, RangeFrom<i32>, RangeTo<u32>, Range<usize>, RangeToInclusive<i32>, RangeInclusive<char>)",
+        type_at_pos(&db, pos),
+    );
+}
+
+#[test]
 fn infer_while_let() {
     let (db, pos) = TestDB::with_position(
         r#"