Add partial deserialization support

Only externally tagged, only named fields or unit variants

tests/deserialize.rs

@@ -0,0 +1,23 @@
+use miniserde::{json, Deserialize};
+use miniserde_enum::Deserialize_enum;
+
+#[test]
+fn test_external() {
+    #[derive(Deserialize_enum, Debug, PartialEq)]
+    enum External {
+        // A(i32),
+        // #[serde(rename = "renamedB")]
+        // B(i32, String),
+        C {
+            x: i32,
+        },
+        // D,
+    }
+    use External::*;
+    // let example = r#"[{"A":21},{"renamedB":[42,"everything"]},{"C":{"x":2}},"D"]"#;
+    let example = r#"[{"C":{"x":2}}]"#;
+    let actual: Vec<External> = json::from_str(example).unwrap();
+    // let expected = [A(21), B(42, "everything".to_string()), C { x: 2 }, D];
+    let expected = vec![C { x: 2 }];
+    assert_eq!(actual, expected);
+}