Add support for enums in top level

Partially address samscott89#71

src/de/mod.rs

@@ -37,14 +37,14 @@
 //! `ParsableStringDeserializer`.
 
 mod parse;
-
 use crate::error::*;
 
 use serde::de;
 use serde::de::IntoDeserializer;
 
 use std::borrow::Cow;
 use std::collections::btree_map::{BTreeMap, Entry, IntoIter};
+use std::iter::Peekable;
 
 /// To override the default serialization parameters, first construct a new
 /// Config.
@@ -190,7 +190,7 @@ pub fn from_str<'de, T: de::Deserialize<'de>>(input: &'de str) -> Result<T> {
 ///
 /// Supported top-level outputs are structs and maps.
 pub(crate) struct QsDeserializer<'a> {
-    iter: IntoIter<Cow<'a, str>, Level<'a>>,
+    iter: Peekable<IntoIter<Cow<'a, str>, Level<'a>>>,
     value: Option<Level<'a>>,
 }
 
@@ -207,7 +207,7 @@ enum Level<'a> {
 impl<'a> QsDeserializer<'a> {
     fn with_map(map: BTreeMap<Cow<'a, str>, Level<'a>>) -> Self {
         QsDeserializer {
-            iter: map.into_iter(),
+            iter: map.into_iter().peekable(),
             value: None,
         }
     }
@@ -225,11 +225,11 @@ impl<'de> de::Deserializer<'de> for QsDeserializer<'de> {
     where
         V: de::Visitor<'de>,
     {
-        if self.iter.next().is_none() {
-            return visitor.visit_unit();
+        if self.iter.peek().is_none() {
+            visitor.visit_unit()
+        } else {
+            self.deserialize_map(visitor)
         }
-
-        Err(Error::top_level("primitive"))
     }
 
     fn deserialize_map<V>(self, visitor: V) -> Result<V::Value>

src/de/parse.rs

@@ -280,8 +280,8 @@ impl<'a> Parser<'a> {
         // Parses all top level nodes into the `root` map.
         while self.parse(&mut root)? {}
         let iter = match root {
-            Level::Nested(map) => map.into_iter(),
-            _ => BTreeMap::default().into_iter(),
+            Level::Nested(map) => map.into_iter().peekable(),
+            _ => BTreeMap::default().into_iter().peekable(),
         };
         Ok(QsDeserializer { iter, value: None })
     }

tests/test_deserialize.rs

@@ -304,6 +304,51 @@ fn deserialize_enum_untagged() {
     );
 }
 
+#[test]
+fn deserialize_enum_untagged_top_level() {
+    #[derive(Deserialize, Debug, PartialEq)]
+    #[serde(untagged)]
+    enum E {
+        B { b: String },
+        S { s: String },
+    }
+
+    let params = "s=true";
+    let rec_params: E = qs::from_str(params).unwrap();
+    assert_eq!(
+        rec_params,
+        E::S {
+            s: "true".to_string()
+        }
+    );
+    let params = "b=test";
+    let rec_params: E = qs::from_str(params).unwrap();
+    assert_eq!(
+        rec_params,
+        E::B {
+            b: "test".to_string()
+        }
+    );
+}
+
+#[test]
+fn deserialize_enum_top_level() {
+    #[derive(Deserialize, Debug, PartialEq)]
+    enum E {
+        B { b: String },
+        S { s: String },
+    }
+
+    let params = "S[s]=test";
+    let rec_params: E = qs::from_str(params).unwrap();
+    assert_eq!(
+        rec_params,
+        E::S {
+            s: "test".to_string()
+        }
+    );
+}
+
 #[test]
 fn deserialize_enum_adjacently() {
     #[derive(Deserialize, Debug, PartialEq)]