Add a test to track known bugs for ron-rs#508

tests/508_value_adjacently_tagged_bug.rs

@@ -0,0 +1,59 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", content = "value")]
+enum TheEnum {
+    Variant([f32; 3]),
+}
+
+#[test]
+fn roundtrip_through_value() {
+    let value = TheEnum::Variant([0.1, 0.1, 0.1]);
+
+    let ron = ron::to_string(&value).unwrap();
+    assert_eq!(ron, "(type:Variant,value:(0.1,0.1,0.1))");
+
+    let de = ron::from_str::<TheEnum>(&ron).unwrap();
+    assert_eq!(de, value);
+
+    let ron_value = ron::from_str::<ron::Value>(&ron).unwrap();
+
+    // Known bug: ron::Value only stores a unit, cannot find a variant
+    let err = ron_value.into_rust::<TheEnum>().unwrap_err();
+    assert_eq!(
+        err,
+        ron::Error::InvalidValueForType {
+            expected: String::from("variant of enum TheEnum"),
+            found: String::from("a unit value")
+        }
+    );
+
+    let old_serde_ron: &str = "(type:\"Variant\",value:(0.1,0.1,0.1))";
+
+    // Known bug: serde no longer uses strings in > v1.0.180 to deserialize the variant
+    let err = ron::from_str::<TheEnum>(&old_serde_ron).unwrap_err();
+    assert_eq!(
+        err,
+        ron::error::SpannedError {
+            code: ron::Error::ExpectedIdentifier,
+            position: ron::error::Position { line: 1, col: 7 },
+        }
+    );
+
+    let ron_value = ron::from_str::<ron::Value>(&old_serde_ron).unwrap();
+
+    // Known bug: ron::Value is asked for an enum but has no special handling for it (yet)
+    let err = ron_value.into_rust::<TheEnum>().unwrap_err();
+    assert_eq!(
+        err,
+        ron::Error::InvalidValueForType {
+            expected: String::from("variant of enum TheEnum"),
+            found: String::from("the string \"Variant\"")
+        }
+    );
+
+    // This still works, but is a bug as well
+    let ron_value = ron::from_str::<ron::Value>("(\"Variant\",(0.1,0.1,0.1))").unwrap();
+    let de: TheEnum = ron_value.into_rust::<TheEnum>().unwrap();
+    assert_eq!(de, value);
+}