add deser support for enum type

Author: fawdlstty

src/idl_gen_rust.cpp

@@ -841,6 +841,27 @@ class RustGenerator : public BaseGenerator {
       code_ += "  }";
       code_ += "}";
       code_ += "";
+
+      code_ += "impl<'de> serde::Deserialize<'de> for {{ENUM_TY}} {";
+      code_ +=
+          "    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>";
+      code_ += "    where";
+      code_ += "        D: serde::Deserializer<'de>,";
+      code_ += "    {";
+      code_ += "        let s = String::deserialize(deserializer)?;";
+      code_ += "        for exp in {{ENUM_TY}}::ENUM_VALUES {";
+      code_ += "            if let Some(exp_name) = exp.variant_name()";
+      code_ += "                && exp_name == s";
+      code_ += "            {";
+      code_ += "                return Ok(exp.clone());";
+      code_ += "            }";
+      code_ += "        }";
+      code_ += "        Err(serde::de::Error::custom(format!(";
+      code_ += "            \"Unknown {{ENUM_TY}} variant: {s}\"";
+      code_ += "        )))";
+      code_ += "    }";
+      code_ += "}";
+      code_ += "";
     }
 
     // Generate Follow and Push so we can serialize and stuff.