message: #[serde(default)] for all config structs
diff: @@ -13,13 +13,15 @@ use std::{collections::HashMap, env};
  /// `.swcrc` file
  #[derive(Debug, Default, Clone, Serialize, Deserialize)]
  pub struct Config {
  + #[serde(default)]
  pub jsc: JscConfig,
  }
  #[derive(Debug, Default, Clone, Serialize, Deserialize)]
  pub struct JscConfig {
  - #[serde(rename = "parser")]
  + #[serde(rename = "parser", default)]
  pub syntax: Syntax,
  + #[serde(default)]
  pub transform: TrnasformConfig,
  }
  @@ -27,16 +29,19 @@ pub struct JscConfig {
  pub struct TrnasformConfig {
  #[serde(default)]
  pub react: react::Options,
  + #[serde(default)]
  pub optimizer: Option<OptimizerConfig>,
  }
  #[derive(Debug, Default, Clone, Serialize, Deserialize)]
  pub struct OptimizerConfig {
  + #[serde(default)]
  pub globals: Option<GlobalPassOption>,
  }
  #[derive(Debug, Default, Clone, Serialize, Deserialize)]
  pub struct GlobalPassOption {
  + #[serde(default)]
  pub vars: FnvHashMap<String, String>,
  }
  