Add serde support to document type. (#2616)

## Description
Implements serde support for `Document`.

## Testing
Test checks whether the serialized/de-serialized data matches with the
expected value

----

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copy, and redistribute this contribution, under the terms of your
choice._

rust-runtime/aws-smithy-types/src/document.rs

@@ -7,6 +7,12 @@ use crate::Number;
 use std::borrow::Cow;
 use std::collections::HashMap;
 
+#[cfg(any(
+    all(aws_sdk_unstable, feature = "serde-deserialize"),
+    all(aws_sdk_unstable, feature = "serde-serialize")
+))]
+use serde;
+
 /* ANCHOR: document */
 
 /// Document Type
@@ -16,6 +22,21 @@ use std::collections::HashMap;
 /// modeled using rigid types, or data that has a schema that evolves outside of the purview of a model.
 /// The serialization format of a document is an implementation detail of a protocol.
 #[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(
+    all(aws_sdk_unstable, feature = "serde-serialize"),
+    derive(serde::Serialize)
+)]
+#[cfg_attr(
+    all(aws_sdk_unstable, feature = "serde-deserialize"),
+    derive(serde::Deserialize)
+)]
+#[cfg_attr(
+    any(
+        all(aws_sdk_unstable, feature = "serde-deserialize"),
+        all(aws_sdk_unstable, feature = "serde-serialize")
+    ),
+    serde(untagged)
+)]
 pub enum Document {
     /// JSON object
     Object(HashMap<String, Document>),
@@ -207,3 +228,60 @@ impl From<Number> for Document {
         Document::Number(value)
     }
 }
+
+/* ANCHOR END: document */
+
+#[cfg(test)]
+mod test {
+    /// checks if a) serialization of json suceeds and b) it is compatible with serde_json
+    #[test]
+    #[cfg(all(
+        aws_sdk_unstable,
+        feature = "serde-serialize",
+        feature = "serde-deserialize"
+    ))]
+    fn serialize_json() {
+        use crate::Document;
+        use crate::Number;
+        use std::collections::HashMap;
+        let mut map: HashMap<String, Document> = HashMap::new();
+        // string
+        map.insert("hello".into(), "world".to_string().into());
+        // numbers
+        map.insert("pos_int".into(), Document::Number(Number::PosInt(1).into()));
+        map.insert(
+            "neg_int".into(),
+            Document::Number(Number::NegInt(-1).into()),
+        );
+        map.insert(
+            "float".into(),
+            Document::Number(Number::Float(0.1 + 0.2).into()),
+        );
+        // booleans
+        map.insert("true".into(), true.into());
+        map.insert("false".into(), false.into());
+        // check if array with different datatypes would succeed
+        map.insert(
+            "array".into(),
+            vec![
+                map.clone().into(),
+                "hello-world".to_string().into(),
+                true.into(),
+                false.into(),
+            ]
+            .into(),
+        );
+        // map
+        map.insert("map".into(), map.clone().into());
+        // null
+        map.insert("null".into(), Document::Null);
+        let obj = Document::Object(map);
+        // comparing string isnt going to work since there is no gurantee for the ordering of the keys
+        let target_file = include_str!("../test_data/serialize_document.json");
+        let json: Result<serde_json::Value, _> = serde_json::from_str(target_file);
+        // serializer
+        assert_eq!(serde_json::to_value(&obj).unwrap(), json.unwrap());
+        let doc: Result<Document, _> = serde_json::from_str(target_file);
+        assert_eq!(obj, doc.unwrap());
+    }
+}

rust-runtime/aws-smithy-types/test_data/serialize_document.json

@@ -0,0 +1,43 @@
+{
+    "null": null,
+    "true": true,
+    "pos_int": 1,
+    "false": false,
+    "map": {
+        "array": [
+            {
+                "pos_int": 1,
+                "float": 0.30000000000000004,
+                "neg_int": -1,
+                "hello": "world",
+                "false": false,
+                "true": true
+            },
+            "hello-world",
+            true,
+            false
+        ],
+        "pos_int": 1,
+        "float": 0.30000000000000004,
+        "neg_int": -1,
+        "hello": "world",
+        "false": false,
+        "true": true
+    },
+    "float": 0.30000000000000004,
+    "neg_int": -1,
+    "hello": "world",
+    "array": [
+        {
+            "pos_int": 1,
+            "float": 0.30000000000000004,
+            "neg_int": -1,
+            "hello": "world",
+            "false": false,
+            "true": true
+        },
+        "hello-world",
+        true,
+        false
+    ]
+}