Fix never in if expressions

2 files changed, 51 insertions, 4 deletions

diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index b310bf6bd..d01063766 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -987,14 +987,21 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 let then_ty = self.infer_expr(*then_branch, expected);
                 match else_branch {
                     Some(else_branch) => {
-                        self.infer_expr(*else_branch, expected);
+                        let else_ty = self.infer_expr(*else_branch, expected);
+                        if Self::is_never(&then_ty) {
+                            tested_by!(if_never);
+                            else_ty
+                        } else {
+                            tested_by!(if_else_never);
+                            then_ty
+                        }
                     }
                     None => {
                         // no else branch -> unit
                         self.unify(&then_ty, &Ty::unit()); // actually coerce
+                        then_ty
                     }
-                };
-                then_ty
+                }
             }
             Expr::Block { statements, tail } => self.infer_block(statements, *tail, expected),
             Expr::TryBlock { body } => {
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 7ec834836..94b0fe3b3 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -3595,7 +3595,7 @@ fn no_such_field_diagnostics() {
     );
 }
 
-mod match_with_never_tests {
+mod branching_with_never_tests {
     use super::type_at;
     use test_utils::covers;
 
@@ -3645,6 +3645,46 @@ fn test(a: i32) {
     }
 
     #[test]
+    fn if_never() {
+        covers!(if_never);
+        let t = type_at(
+            r#"
+//- /main.rs
+fn test() {
+    let i = if true {
+        loop {}
+    } else {
+        3.0
+    };
+    i<|>
+    ()
+}
+"#,
+        );
+        assert_eq!(t, "f64");
+    }
+
+    #[test]
+    fn if_else_never() {
+        covers!(if_else_never);
+        let t = type_at(
+            r#"
+//- /main.rs
+fn test(input: bool) {
+    let i = if input {
+        2.0
+    } else {
+        return
+    };
+    i<|>
+    ()
+}
+"#,
+        );
+        assert_eq!(t, "f64");
+    }
+
+    #[test]
     fn match_second_arm_never() {
         covers!(match_second_arm_never);
         let t = type_at(