Fix annoying 'invalid type: unit value, expected struct Settings' error

Author: tyranron

src/config.rs

@@ -10,7 +10,7 @@ use ser::ConfigSerializer;
 use source::Source;
 
 use path;
-use value::{Value, ValueKind, ValueWithKey};
+use value::{Table, Value, ValueKind, ValueWithKey};
 
 #[derive(Clone, Debug)]
 enum ConfigKind {
@@ -49,7 +49,12 @@ pub struct Config {
 
 impl Config {
     pub fn new() -> Self {
-        Config::default()
+        Self {
+            kind: ConfigKind::default(),
+            // Config root should be instantiated as an empty table
+            // to avoid deserialization errors.
+            cache: Value::new(None, Table::new()),
+        }
     }
 
     /// Merge in a configuration property source.

tests/empty.rs

@@ -0,0 +1,21 @@
+extern crate config;
+
+#[macro_use]
+extern crate serde_derive;
+
+use config::*;
+
+#[derive(Debug, Serialize, Deserialize)]
+struct Settings {
+    #[serde(skip)]
+    foo: isize,
+    #[serde(skip)]
+    bar: u8,
+}
+
+#[test]
+fn empty_deserializes() {
+    let s: Settings = Config::new().try_into().expect("Deserialization failed");
+    assert_eq!(s.foo, 0);
+    assert_eq!(s.bar, 0);
+}