Do not require enabled_lints property in .elp_lint.toml

Summary: We were not deriving `default`, so the field was actually required. I suspect this was not intentional.

Reviewed By: alanz

Differential Revision: D69594761

fbshipit-source-id: c9e0fd3b5790a10f74923cbf956dbcf80646d4d4

crates/elp/src/lib.rs

@@ -215,4 +215,14 @@ mod tests {
         "#]]
         .assert_eq(&toml::to_string::<LintConfig>(&lint_config).unwrap());
     }
+
+    #[test]
+    fn serde_read_lint_config_empty_enabled() {
+        let content = r#"
+            disabled_lints = []
+            "#;
+        let config = toml::from_str::<LintConfig>(&content).unwrap();
+        assert_eq!(config.enabled_lints, vec![]);
+        assert_eq!(config.disabled_lints, vec![]);
+    }
 }

crates/ide/src/diagnostics.rs

@@ -659,6 +659,7 @@ impl DiagnosticsConfig {
 /// initially.  But could by anything supported by serde.
 #[derive(Deserialize, Serialize, Default, Debug)]
 pub struct LintConfig {
+    #[serde(default)]
     pub enabled_lints: Vec<DiagnosticCode>,
     #[serde(default)]
     pub disabled_lints: Vec<DiagnosticCode>,