Fix code actions migration (#40303)

Closes #40270

Release Notes:

- Fixed an issue with the settings migration to flatten `code_actions`
format steps where comments would cause enabled code actions to be
omitted from the migrated settings. If you were effected, restoring the
settings file backup and allowing the migration to re-run will result in
a valid settings file
- Fixed an issue where automated settings and keymap file updates would
occasionally assume 4-space indentation

crates/migrator/src/patterns/settings.rs

@@ -108,3 +108,24 @@ pub const SETTINGS_DUPLICATED_AGENT_PATTERN: &str = r#"(document
     (#eq? @agent1 "agent")
     (#eq? @agent2 "agent")
 )"#;
+
+/// Migrate language settings,
+/// calls `migrate_fn` with the top level object as well as all language settings under the "languages" key
+/// Fails early if `migrate_fn` returns an error at any point
+pub fn migrate_language_setting(
+    value: &mut serde_json::Value,
+    migrate_fn: fn(&mut serde_json::Value, path: &[&str]) -> anyhow::Result<()>,
+) -> anyhow::Result<()> {
+    migrate_fn(value, &[])?;
+    let languages = value
+        .as_object_mut()
+        .and_then(|obj| obj.get_mut("languages"))
+        .and_then(|languages| languages.as_object_mut());
+    if let Some(languages) = languages {
+        for (language_name, language) in languages.iter_mut() {
+            let path = vec!["languages", language_name];
+            migrate_fn(language, &path)?;
+        }
+    }
+    Ok(())
+}