Add roundtrip testing and bump format version

Cargo.lock

@@ -1,5 +1,7 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "addr2line"
 version = "0.14.0"
@@ -4568,6 +4570,7 @@ name = "rustdoc-json-types"
 version = "0.1.0"
 dependencies = [
  "serde",
+ "serde_json",
 ]
 
 [[package]]

src/librustdoc/json/mod.rs

@@ -242,7 +242,7 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
                     )
                 })
                 .collect(),
-            format_version: 4,
+            format_version: 5,
         };
         let mut p = self.out_path.clone();
         p.push(output.index.get(&output.root).unwrap().name.clone().unwrap());

src/rustdoc-json-types/Cargo.toml

@@ -9,3 +9,6 @@ path = "lib.rs"
 
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
+
+[dev-dependencies]
+serde_json = "1.0"

src/rustdoc-json-types/lib.rs

@@ -508,3 +508,47 @@ pub struct Static {
     pub mutable: bool,
     pub expr: String,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_struct_info_roundtrip() {
+        let s = ItemEnum::Struct(Struct {
+            struct_type: StructType::Plain,
+            generics: Generics {
+                params: vec![],
+                where_predicates: vec![]
+            },
+            fields_stripped: false,
+            fields: vec![],
+            impls: vec![],
+        });
+
+        let struct_json = serde_json::to_string(&s).unwrap();
+
+        let de_s = serde_json::from_str(&struct_json).unwrap();
+
+        assert_eq!(s, de_s);
+    }
+
+    #[test]
+    fn test_union_info_roundtrip() {
+        let u = ItemEnum::Union(Union {
+            generics: Generics {
+                params: vec![],
+                where_predicates: vec![]
+            },
+            fields_stripped: false,
+            fields: vec![],
+            impls: vec![],
+        });
+
+        let union_json = serde_json::to_string(&u).unwrap();
+
+        let de_u = serde_json::from_str(&union_json).unwrap();
+
+        assert_eq!(u, de_u);
+    }
+}