Support nullable fields in the Rust generator (#2353)

* Use Option for nullable fields in Rust (closes #2337)

* Update Rust's petstore

modules/openapi-generator/src/main/resources/rust/model.mustache

@@ -15,7 +15,7 @@ pub struct {{{classname}}} {
     /// {{{description}}}
     {{/description}}
     #[serde(rename = "{{{baseName}}}")]
-    pub {{{name}}}: {{^required}}Option<{{/required}}{{{dataType}}}{{^required}}>{{/required}},
+    pub {{{name}}}: {{#required}}{{#isNullable}}Option<{{/isNullable}}{{/required}}{{^required}}Option<{{/required}}{{{dataType}}}{{#required}}{{#isNullable}}>{{/isNullable}}{{/required}}{{^required}}>{{/required}},
 {{/vars}}
 }
 
@@ -23,7 +23,7 @@ impl {{{classname}}} {
     {{#description}}
     /// {{{description}}}
     {{/description}}
-    pub fn new({{#requiredVars}}{{{name}}}: {{{dataType}}}{{^-last}}, {{/-last}}{{/requiredVars}}) -> {{{classname}}} {
+    pub fn new({{#requiredVars}}{{{name}}}: {{#isNullable}}Option<{{/isNullable}}{{{dataType}}}{{#isNullable}}>{{/isNullable}}{{^-last}}, {{/-last}}{{/requiredVars}}) -> {{{classname}}} {
         {{{classname}}} {
             {{#vars}}
             {{{name}}}: {{#required}}{{{name}}}{{/required}}{{^required}}{{#isListContainer}}None{{/isListContainer}}{{#isMapContainer}}None{{/isMapContainer}}{{^isContainer}}None{{/isContainer}}{{/required}},

samples/client/petstore/rust/docs/InlineObject.md

@@ -0,0 +1,11 @@
+# InlineObject
+
+## Properties
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**name** | **String** | Updated name of the pet | [optional] 
+**status** | **String** | Updated status of the pet | [optional] 
+
+[[Back to Model list]](../README.md#documentation-for-models) [[Back to API list]](../README.md#documentation-for-api-endpoints) [[Back to README]](../README.md)
+
+

samples/client/petstore/rust/docs/InlineObject1.md

@@ -0,0 +1,11 @@
+# InlineObject1
+
+## Properties
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**additional_metadata** | **String** | Additional data to pass to server | [optional] 
+**file** | [***&std::path::Path**](&std::path::Path.md) | file to upload | [optional] 
+
+[[Back to Model list]](../README.md#documentation-for-models) [[Back to API list]](../README.md#documentation-for-api-endpoints) [[Back to README]](../README.md)
+
+

samples/client/petstore/rust/src/models/inline_object.rs

@@ -0,0 +1,32 @@
+/*
+ * OpenAPI Petstore
+ *
+ * This is a sample server Petstore server. For this sample, you can use the api key `special-key` to test the authorization filters.
+ *
+ * OpenAPI spec version: 1.0.0
+ * 
+ * Generated by: https://openapi-generator.tech
+ */
+
+
+#[allow(unused_imports)]
+use serde_json::Value;
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct InlineObject {
+    /// Updated name of the pet
+    #[serde(rename = "name")]
+    pub name: Option<String>,
+    /// Updated status of the pet
+    #[serde(rename = "status")]
+    pub status: Option<String>,
+}
+
+impl InlineObject {
+    pub fn new() -> InlineObject {
+        InlineObject {
+            name: None,
+            status: None,
+        }
+    }
+}

samples/client/petstore/rust/src/models/inline_object_1.rs

@@ -0,0 +1,32 @@
+/*
+ * OpenAPI Petstore
+ *
+ * This is a sample server Petstore server. For this sample, you can use the api key `special-key` to test the authorization filters.
+ *
+ * OpenAPI spec version: 1.0.0
+ * 
+ * Generated by: https://openapi-generator.tech
+ */
+
+
+#[allow(unused_imports)]
+use serde_json::Value;
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct InlineObject1 {
+    /// Additional data to pass to server
+    #[serde(rename = "additionalMetadata")]
+    pub additional_metadata: Option<String>,
+    /// file to upload
+    #[serde(rename = "file")]
+    pub file: Option<&std::path::Path>,
+}
+
+impl InlineObject1 {
+    pub fn new() -> InlineObject1 {
+        InlineObject1 {
+            additional_metadata: None,
+            file: None,
+        }
+    }
+}