Add regression test

src/test/ui/issues/issue-78115.rs

@@ -0,0 +1,19 @@
+// Regression test for issue #78115: "ICE: variable should be placed in scope earlier"
+
+// check-pass
+// edition:2018
+
+#[allow(dead_code)]
+struct Foo {
+    a: ()
+}
+
+async fn _bar() {
+    let foo = Foo { a: () };
+    match foo {
+        Foo { a: _a } | Foo { a: _a } if true => {}
+        _ => {}
+    }
+}
+
+fn main() {}