feat: migrate legacy fields.json on first 0.2 launch

src/ui/main_window.rs

@@ -46,16 +46,7 @@ impl MainWindow {
                             Ok(settings_dir) => {
                                 let fields_file = settings_dir.join(SETTINGS_FILE);
                                 match fs::read(fields_file) {
-                                    Ok(content) => match serde_json::from_slice::<Self>(&content) {
-                                        Ok(obj) => {
-                                            self.tab_daplink = obj.tab_daplink;
-                                            self.tab_ws = obj.tab_ws;
-                                            println!("Settings loaded !");
-                                        }
-                                        Err(e) => {
-                                            eprintln!("Failed to deserialize settings. Error: {e}");
-                                        }
-                                    },
+                                    Ok(content) => self.load_settings(&content),
                                     Err(e) => eprintln!("Failed to open settings file ({e})"),
                                 }
                             }
@@ -112,4 +103,104 @@ impl MainWindow {
     pub fn application_subscription(&self) -> Subscription<Message> {
         event::listen().map(Message::ApplicationEvent)
     }
+
+    /// Deserialize the on-disk settings, with a fallback to the legacy 0.1.x
+    /// schema where `TabDaplink` fields were serialized directly at the top
+    /// level and are now mapped onto `tab_daplink`. Successful migrations get
+    /// rewritten in the new shape on the next `CloseRequested`.
+    fn load_settings(&mut self, content: &[u8]) {
+        match serde_json::from_slice::<Self>(content) {
+            Ok(obj) => {
+                self.tab_daplink = obj.tab_daplink;
+                self.tab_ws = obj.tab_ws;
+                println!("Settings loaded !");
+            }
+            Err(new_err) => match serde_json::from_slice::<TabDaplink>(content) {
+                Ok(legacy) => {
+                    self.tab_daplink = legacy;
+                    println!("Legacy settings migrated to the new schema");
+                }
+                Err(legacy_err) => {
+                    eprintln!(
+                        "Failed to deserialize settings. New schema error: {new_err}. Legacy schema error: {legacy_err}"
+                    );
+                }
+            },
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const LEGACY_JSON: &[u8] = br#"{
+        "bootloader_path": "/tmp/bl.bin",
+        "firmware_path": "/tmp/fw.bin",
+        "user_file_path": "/tmp/user.bin",
+        "target_waiting_time": 7,
+        "target_name": "LEGACY-STEAMI"
+    }"#;
+
+    const NEW_JSON: &[u8] = br#"{
+        "tab_daplink": {
+            "bootloader_path": "/tmp/bl.bin",
+            "firmware_path": "/tmp/fw.bin",
+            "user_file_path": "/tmp/user.bin",
+            "target_waiting_time": 7,
+            "target_name": "LEGACY-STEAMI"
+        },
+        "tab_ws": {
+            "fw_selected": "BleHciExt"
+        }
+    }"#;
+
+    #[test]
+    fn loads_new_schema() {
+        let mut w = MainWindow::default();
+        w.load_settings(NEW_JSON);
+        let s = serde_json::to_string(&w).unwrap();
+        assert!(s.contains(r#""target_name":"LEGACY-STEAMI""#));
+        assert!(s.contains(r#""fw_selected":"BleHciExt""#));
+    }
+
+    #[test]
+    fn legacy_schema_migrates_and_serializes_in_new_shape() {
+        let mut w = MainWindow::default();
+        w.load_settings(LEGACY_JSON);
+
+        // Re-serialize the way the CloseRequested handler does.
+        let s = serde_json::to_string(&w).unwrap();
+
+        // New shape: top-level keys for both tabs.
+        assert!(s.contains(r#""tab_daplink""#), "missing tab_daplink in: {s}");
+        assert!(s.contains(r#""tab_ws""#), "missing tab_ws in: {s}");
+
+        // Legacy data preserved under tab_daplink.
+        assert!(s.contains(r#""bootloader_path":"/tmp/bl.bin""#));
+        assert!(s.contains(r#""firmware_path":"/tmp/fw.bin""#));
+        assert!(s.contains(r#""user_file_path":"/tmp/user.bin""#));
+        assert!(s.contains(r#""target_waiting_time":7"#));
+        assert!(s.contains(r#""target_name":"LEGACY-STEAMI""#));
+    }
+
+    #[test]
+    fn malformed_json_keeps_defaults() {
+        let mut w = MainWindow::default();
+        w.load_settings(b"{ this is not json");
+        // No assertion on stderr — load_settings reports both errors via eprintln,
+        // exercised manually. The state must remain at defaults: serializing
+        // shouldn't carry any of the malformed input.
+        let s = serde_json::to_string(&w).unwrap();
+        assert!(!s.contains("LEGACY-STEAMI"));
+    }
+
+    #[test]
+    fn empty_content_keeps_defaults() {
+        let mut w = MainWindow::default();
+        w.load_settings(b"");
+        let s = serde_json::to_string(&w).unwrap();
+        assert!(s.contains(r#""tab_daplink""#));
+        assert!(s.contains(r#""tab_ws""#));
+    }
 }