Read the list of locales from /etc/agama.d (#1205)

To reduce the size of the live image as much as possible, we remove the
[locales
data](https://github.com/openSUSE/agama/blob/master/live/src/config.sh#L61-L69).
The only exceptions are those locales that contain Agama translations.
As a consequence, Agama cannot find the list of locales.

After some discussion, we agreed to read a static list (in
`/etc/agama.d/locales`). If the list is not there, it keeps running
`localectl list-units`.

rust/agama-server/src/l10n/locale.rs

@@ -5,7 +5,7 @@ use agama_locale_data::{InvalidLocaleCode, LocaleId};
 use anyhow::Context;
 use serde::Serialize;
 use serde_with::{serde_as, DisplayFromStr};
-use std::process::Command;
+use std::{fs, process::Command};
 
 /// Represents a locale, including the localized language and territory.
 #[serde_as]
@@ -37,15 +37,12 @@ impl LocalesDatabase {
 
     /// Loads the list of locales.
     ///
+    /// It checks for a file in /etc/agama.d/locales containing the list of supported locales (one per line).
+    /// It it does not exists, calls `localectl list-locales`.
+    ///
     /// * `ui_language`: language to translate the descriptions (e.g., "en").
     pub fn read(&mut self, ui_language: &str) -> Result<(), Error> {
-        let result = Command::new("localectl")
-            .args(["list-locales"])
-            .output()
-            .context("Failed to get the list of locales")?;
-        let output =
-            String::from_utf8(result.stdout).context("Invalid UTF-8 sequence from list-locales")?;
-        self.known_locales = output
+        self.known_locales = Self::get_locales_list()?
             .lines()
             .filter_map(|line| TryInto::<LocaleId>::try_into(line).ok())
             .collect();
@@ -110,6 +107,20 @@ impl LocalesDatabase {
 
         Ok(result)
     }
+
+    fn get_locales_list() -> Result<String, Error> {
+        const LOCALES_LIST_PATH: &str = "/etc/agama.d/locales";
+
+        if let Ok(locales) = fs::read_to_string(LOCALES_LIST_PATH) {
+            return Ok(locales);
+        }
+
+        let result = Command::new("localectl")
+            .args(["list-locales"])
+            .output()
+            .context("Failed to get the list of locales")?;
+        Ok(String::from_utf8(result.stdout).context("Invalid UTF-8 sequence from list-locales")?)
+    }
 }
 
 #[cfg(test)]

rust/package/agama.changes

@@ -1,3 +1,9 @@
+-------------------------------------------------------------------
+Tue May 14 12:39:49 UTC 2024 - Imobach Gonzalez Sosa <igonzalezsosa@suse.com>
+
+- If present, read the locales list from the /etc/agama.d/locales
+  file (gh#openSUSE/agama#1205).
+
 -------------------------------------------------------------------
 Tue May 14 10:48:42 UTC 2024 - Knut Anderssen <kanderssen@suse.com>