6 files changed, 172 insertions, 11 deletions

diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index bbbc391c4..e97b81473 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -196,7 +196,12 @@ struct InferenceContext<'a, D: HirDatabase> {
     trait_env: Arc<TraitEnvironment>,
     obligations: Vec<Obligation>,
     result: InferenceResult,
-    /// The return type of the function being inferred.
+    /// The return type of the function being inferred, or the closure if we're
+    /// currently within one.
+    ///
+    /// We might consider using a nested inference context for checking
+    /// closures, but currently this is the only field that will change there,
+    /// so it doesn't make sense.
     return_ty: Ty,
 
     /// Impls of `CoerceUnsized` used in coercion.
@@ -455,7 +460,7 @@ 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()));
+        self.infer_expr_coerce(self.body.body_expr, &Expectation::has_type(self.return_ty.clone()));
     }
 
     fn resolve_into_iter_item(&self) -> Option<TypeAliasId> {
diff --git a/crates/ra_hir_ty/src/infer/coerce.rs b/crates/ra_hir_ty/src/infer/coerce.rs
index 0f4dac45e..83c0c2c3f 100644
--- a/crates/ra_hir_ty/src/infer/coerce.rs
+++ b/crates/ra_hir_ty/src/infer/coerce.rs
@@ -134,6 +134,10 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 }
             }
 
+            (ty_app!(TypeCtor::Closure { .. }, params), ty_app!(TypeCtor::FnPtr { .. })) => {
+                from_ty = params[0].clone();
+            }
+
             _ => {}
         }
 
diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index 8be567917..3af05394c 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -41,7 +41,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
 
     /// Infer type of expression with possibly implicit coerce to the expected type.
     /// Return the type after possible coercion.
-    fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
+    pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
         let ty = self.infer_expr_inner(expr, &expected);
         let ty = if !self.coerce(&ty, &expected.ty) {
             self.result
@@ -102,7 +102,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
                 Ty::unit()
             }
-            Expr::Lambda { body, args, arg_types } => {
+            Expr::Lambda { body, args, ret_type, arg_types } => {
                 assert_eq!(args.len(), arg_types.len());
 
                 let mut sig_tys = Vec::new();
@@ -118,7 +118,10 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 }
 
                 // add return type
-                let ret_ty = self.table.new_type_var();
+                let ret_ty = match ret_type {
+                    Some(type_ref) => self.make_ty(type_ref),
+                    None => self.table.new_type_var(),
+                };
                 sig_tys.push(ret_ty.clone());
                 let sig_ty = Ty::apply(
                     TypeCtor::FnPtr { num_args: sig_tys.len() as u16 - 1 },
@@ -134,7 +137,12 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 // infer the body.
                 self.coerce(&closure_ty, &expected.ty);
 
-                self.infer_expr(*body, &Expectation::has_type(ret_ty));
+                let prev_ret_ty = std::mem::replace(&mut self.return_ty, ret_ty.clone());
+
+                self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
+
+                self.return_ty = prev_ret_ty;
+
                 closure_ty
             }
             Expr::Call { callee, args } => {
@@ -192,6 +200,9 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             Expr::Return { expr } => {
                 if let Some(expr) = expr {
                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
+                } else {
+                    let unit = Ty::unit();
+                    self.coerce(&unit, &self.return_ty.clone());
                 }
                 Ty::simple(TypeCtor::Never)
             }
diff --git a/crates/ra_hir_ty/src/tests/coercion.rs b/crates/ra_hir_ty/src/tests/coercion.rs
index ac9e3872a..7e99a42ed 100644
--- a/crates/ra_hir_ty/src/tests/coercion.rs
+++ b/crates/ra_hir_ty/src/tests/coercion.rs
@@ -370,6 +370,22 @@ fn test() {
 }
 
 #[test]
+fn return_coerce_unknown() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+fn foo() -> u32 {
+    return unknown;
+}
+"#, true),
+        @r###"
+    [17; 40) '{     ...own; }': !
+    [23; 37) 'return unknown': !
+    [30; 37) 'unknown': u32
+    "###
+    );
+}
+
+#[test]
 fn coerce_autoderef() {
     assert_snapshot!(
         infer_with_mismatches(r#"
@@ -440,3 +456,73 @@ fn test() {
     "###
     );
 }
+
+#[test]
+fn closure_return_coerce() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+fn foo() {
+    let x = || {
+        if true {
+            return &1u32;
+        }
+        &&1u32
+    };
+}
+"#, true),
+        @r###"
+    [10; 106) '{     ...  }; }': ()
+    [20; 21) 'x': || -> &u32
+    [24; 103) '|| {  ...     }': || -> &u32
+    [27; 103) '{     ...     }': &u32
+    [37; 82) 'if tru...     }': ()
+    [40; 44) 'true': bool
+    [45; 82) '{     ...     }': !
+    [59; 71) 'return &1u32': !
+    [66; 71) '&1u32': &u32
+    [67; 71) '1u32': u32
+    [91; 97) '&&1u32': &&u32
+    [92; 97) '&1u32': &u32
+    [93; 97) '1u32': u32
+    "###
+    );
+}
+
+#[test]
+fn coerce_fn_item_to_fn_ptr() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+fn foo(x: u32) -> isize { 1 }
+fn test() {
+    let f: fn(u32) -> isize = foo;
+}
+"#, true),
+        @r###"
+    [8; 9) 'x': u32
+    [25; 30) '{ 1 }': isize
+    [27; 28) '1': isize
+    [41; 79) '{     ...foo; }': ()
+    [51; 52) 'f': fn(u32) -> isize
+    [73; 76) 'foo': fn foo(u32) -> isize
+    "###
+    );
+}
+
+#[test]
+fn coerce_closure_to_fn_ptr() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+fn test() {
+    let f: fn(u32) -> isize = |x| { 1 };
+}
+"#, true),
+        @r###"
+    [11; 55) '{     ...1 }; }': ()
+    [21; 22) 'f': fn(u32) -> isize
+    [43; 52) '|x| { 1 }': |u32| -> isize
+    [44; 45) 'x': u32
+    [47; 52) '{ 1 }': isize
+    [49; 50) '1': isize
+    "###
+    );
+}
diff --git a/crates/ra_hir_ty/src/tests/simple.rs b/crates/ra_hir_ty/src/tests/simple.rs
index 18976c9ae..6fe647a5e 100644
--- a/crates/ra_hir_ty/src/tests/simple.rs
+++ b/crates/ra_hir_ty/src/tests/simple.rs
@@ -1606,3 +1606,58 @@ fn main() {
     );
     assert_eq!(t, "u32");
 }
+
+#[test]
+fn closure_return() {
+    assert_snapshot!(
+        infer(r#"
+fn foo() -> u32 {
+    let x = || -> usize { return 1; };
+}
+"#),
+        @r###"
+    [17; 59) '{     ...; }; }': ()
+    [27; 28) 'x': || -> usize
+    [31; 56) '|| -> ...n 1; }': || -> usize
+    [43; 56) '{ return 1; }': !
+    [45; 53) 'return 1': !
+    [52; 53) '1': usize
+    "###
+    );
+}
+
+#[test]
+fn closure_return_unit() {
+    assert_snapshot!(
+        infer(r#"
+fn foo() -> u32 {
+    let x = || { return; };
+}
+"#),
+        @r###"
+    [17; 48) '{     ...; }; }': ()
+    [27; 28) 'x': || -> ()
+    [31; 45) '|| { return; }': || -> ()
+    [34; 45) '{ return; }': !
+    [36; 42) 'return': !
+    "###
+    );
+}
+
+#[test]
+fn closure_return_inferred() {
+    assert_snapshot!(
+        infer(r#"
+fn foo() -> u32 {
+    let x = || { "test" };
+}
+"#),
+        @r###"
+    [17; 47) '{     ..." }; }': ()
+    [27; 28) 'x': || -> &str
+    [31; 44) '|| { "test" }': || -> &str
+    [34; 44) '{ "test" }': &str
+    [36; 42) '"test"': &str
+    "###
+    );
+}
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index 2d92a5eec..76e2198b6 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -393,11 +393,11 @@ fn test() -> u64 {
     [54; 55) 'a': S
     [58; 59) 'S': S(fn(u32) -> u64) -> S
     [58; 68) 'S(|i| 2*i)': S
-    [60; 67) '|i| 2*i': |i32| -> i32
-    [61; 62) 'i': i32
-    [64; 65) '2': i32
-    [64; 67) '2*i': i32
-    [66; 67) 'i': i32
+    [60; 67) '|i| 2*i': |u32| -> u64
+    [61; 62) 'i': u32
+    [64; 65) '2': u32
+    [64; 67) '2*i': u32
+    [66; 67) 'i': u32
     [78; 79) 'b': u64
     [82; 83) 'a': S
     [82; 85) 'a.0': fn(u32) -> u64