Merge #3857

3857: Fix inference of function pointer return types r=flodiebold a=lnicola

Fixes #3852.

r? @flodiebold

Co-authored-by: Laurențiu Nicola <lnicola@dend.ro>

crates/ra_hir_def/src/type_ref.rs

@@ -93,7 +93,11 @@ impl TypeRef {
             }
             ast::TypeRef::PlaceholderType(_inner) => TypeRef::Placeholder,
             ast::TypeRef::FnPointerType(inner) => {
-                let ret_ty = TypeRef::from_ast_opt(inner.ret_type().and_then(|rt| rt.type_ref()));
+                let ret_ty = inner
+                    .ret_type()
+                    .and_then(|rt| rt.type_ref())
+                    .map(TypeRef::from_ast)
+                    .unwrap_or_else(|| TypeRef::Tuple(Vec::new()));
                 let mut params = if let Some(pl) = inner.param_list() {
                     pl.params().map(|p| p.ascribed_type()).map(TypeRef::from_ast_opt).collect()
                 } else {

crates/ra_hir_ty/src/tests/simple.rs

@@ -1729,3 +1729,29 @@ fn foo() -> u32 {
     "###
     );
 }
+
+#[test]
+fn fn_pointer_return() {
+    assert_snapshot!(
+        infer(r#"
+struct Vtable {
+    method: fn(),
+}
+
+fn main() {
+    let vtable = Vtable { method: || {} };
+    let m = vtable.method;
+}
+"#),
+        @r###"
+    [48; 121) '{     ...hod; }': ()
+    [58; 64) 'vtable': Vtable
+    [67; 91) 'Vtable...| {} }': Vtable
+    [84; 89) '|| {}': || -> ()
+    [87; 89) '{}': ()
+    [101; 102) 'm': fn() -> ()
+    [105; 111) 'vtable': Vtable
+    [105; 118) 'vtable.method': fn() -> ()
+    "###
+    );
+}