only dump defaults for stable configs when running stable rustfmt

src/bin/main.rs

@@ -214,7 +214,12 @@ fn execute(opts: &Options) -> Result<i32> {
             Ok(0)
         }
         Operation::ConfigOutputDefault { path } => {
-            let toml = Config::default().all_options().to_toml()?;
+            let toml = if is_nightly() {
+                Config::default().all_options().to_toml()?
+            } else {
+                Config::default().stable_options().to_toml()?
+            };
+
             if let Some(path) = path {
                 let mut file = File::create(path)?;
                 file.write_all(toml.as_bytes())?;

src/config/config_type.rs

@@ -237,6 +237,22 @@ macro_rules! create_config {
                 }
             }
 
+
+            #[allow(unreachable_pub)]
+            pub fn stable_options(&self) -> PartialConfig {
+                PartialConfig {
+                    $(
+                        $i: if $stb {
+                                Some(self.$i.2.clone())
+                            } else {
+                                None
+                            },
+                    )+
+                }
+            }
+
+
+
             #[allow(unreachable_pub)]
             pub fn override_value(&mut self, key: &str, val: &str)
             {

src/config/mod.rs

@@ -603,8 +603,9 @@ mod test {
         assert_eq!(s.contains(PRINT_DOCS_PARTIALLY_UNSTABLE_OPTION), true);
     }
 
+    #[nightly_only_test]
     #[test]
-    fn test_dump_default_config() {
+    fn test_dump_all_default_config() {
         let default_config = format!(
             r#"max_width = 100
 hard_tabs = false
@@ -690,6 +691,39 @@ make_backup = false
         assert_eq!(&toml, &default_config);
     }
 
+    #[stable_only_test]
+    #[test]
+    fn test_dump_stable_default_config() {
+        let default_config = r#"max_width = 100
+hard_tabs = false
+tab_spaces = 4
+newline_style = "Auto"
+use_small_heuristics = "Default"
+fn_call_width = 60
+attr_fn_like_width = 70
+struct_lit_width = 18
+struct_variant_width = 35
+array_width = 60
+chain_width = 60
+single_line_if_else_max_width = 50
+reorder_imports = true
+reorder_modules = true
+remove_nested_parens = true
+short_array_element_width_threshold = 10
+match_arm_leading_pipes = "Never"
+fn_params_layout = "Tall"
+match_block_trailing_comma = false
+edition = "2015"
+merge_derives = true
+use_try_shorthand = false
+use_field_init_shorthand = false
+force_explicit_abi = true
+disable_all_formatting = false
+"#;
+        let toml = Config::default().stable_options().to_toml().unwrap();
+        assert_eq!(&toml, &default_config);
+    }
+
     #[stable_only_test]
     #[test]
     fn test_as_not_nightly_channel() {