From 43df7c3d53198e8ae3509035eb5273d8a94f758b Mon Sep 17 00:00:00 2001
From: Florian Diebold <flodiebold@gmail.com>
Date: Tue, 11 Feb 2020 21:07:18 +0100
Subject: [PATCH] Don't let unknown match arms fall back to !

---
 crates/ra_hir_ty/src/infer/expr.rs       |  6 +++++-
 crates/ra_hir_ty/src/tests/never_type.rs | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index 186857b8b2..39d8bc0ca4 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -165,7 +165,11 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             Expr::Match { expr, arms } => {
                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 
-                let mut result_ty = self.table.new_maybe_never_type_var();
+                let mut result_ty = if arms.len() == 0 {
+                    Ty::simple(TypeCtor::Never)
+                } else {
+                    self.table.new_type_var()
+                };
 
                 for arm in arms {
                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
diff --git a/crates/ra_hir_ty/src/tests/never_type.rs b/crates/ra_hir_ty/src/tests/never_type.rs
index c202f545a3..a772094804 100644
--- a/crates/ra_hir_ty/src/tests/never_type.rs
+++ b/crates/ra_hir_ty/src/tests/never_type.rs
@@ -101,6 +101,7 @@ fn test() {
     );
     assert_eq!(t, "Option<i32>");
 }
+
 #[test]
 fn never_type_can_be_reinferred3() {
     let t = type_at(
@@ -137,6 +138,22 @@ fn test(a: Void) {
     assert_eq!(t, "!");
 }
 
+#[test]
+fn match_unknown_arm() {
+    let t = type_at(
+        r#"
+//- /main.rs
+fn test(a: Option) {
+    let t = match 0 {
+        _ => unknown,
+    };
+    t<|>;
+}
+"#,
+    );
+    assert_eq!(t, "{unknown}");
+}
+
 #[test]
 fn if_never() {
     let t = type_at(