Fix store setter to preserve internal migration data

Fixes #114

Author: sindresorhus

source/index.ts

@@ -376,6 +376,18 @@ export default class Conf<T extends Record<string, any> = Record<string, unknown
 	set store(value: T) {
 		this._ensureDirectory();
 
+		// Preserve existing internal data if it exists and the new value doesn't contain it
+		if (!hasProperty(value, INTERNAL_KEY)) {
+			try {
+				const currentStore = this.store;
+				if (hasProperty(currentStore, INTERNAL_KEY)) {
+					setProperty(value, INTERNAL_KEY, getProperty(currentStore, INTERNAL_KEY));
+				}
+			} catch {
+				// If we can't read the current store, just proceed without preserving internal data
+			}
+		}
+
 		this._validate(value);
 		this._write(value);
 

test/index.ts

@@ -1173,3 +1173,105 @@ test('beforeEachMigration - should be called before every migration', t => {
 	t.true(conf.get('beforeEachMigration 1.0.0 → 1.0.1'));
 	t.false(conf.has('beforeEachMigration 1.0.1 → 2.0.1'));
 });
+
+test('migrations - should preserve internal data when store is overwritten', t => {
+	const cwd = temporaryDirectory();
+	let migrationRunCount = 0;
+
+	// Create a config with migrations
+	const conf = new Conf({
+		cwd,
+		projectVersion: '2.0.0',
+		migrations: {
+			'2.0.0'(store) {
+				migrationRunCount++;
+				store.set('lastSeenVersion', '2.0.0');
+			},
+		},
+	});
+
+	// Migration should run once initially
+	t.is(migrationRunCount, 1);
+	t.is(conf.get('__internal__.migrations.version'), '2.0.0');
+
+	// Overwrite the store - this should NOT destroy the migration info
+	conf.store = {newData: 'test'};
+
+	// The internal migration version should still be preserved
+	t.is(conf.get('__internal__.migrations.version'), '2.0.0');
+
+	// Create a new config instance - migration should NOT run again
+	const conf2 = new Conf({
+		cwd,
+		projectVersion: '2.0.0',
+		migrations: {
+			'2.0.0'(store) {
+				migrationRunCount++;
+				store.set('lastSeenVersion', '2.0.0');
+			},
+		},
+	});
+
+	// Migration should not run again
+	t.is(migrationRunCount, 1);
+	t.is(conf2.get('__internal__.migrations.version'), '2.0.0');
+});
+
+test('migrations - should preserve internal data when store is set to empty object', t => {
+	const cwd = temporaryDirectory();
+
+	const conf = new Conf({
+		cwd,
+		projectVersion: '1.0.0',
+		migrations: {
+			'1.0.0'(store) {
+				store.set('migrated', true);
+			},
+		},
+	});
+
+	t.is(conf.get('__internal__.migrations.version'), '1.0.0');
+
+	// Set store to empty object
+	conf.store = {};
+
+	// Internal data should still be preserved
+	t.is(conf.get('__internal__.migrations.version'), '1.0.0');
+});
+
+test('store setter - should work when config file does not exist yet', t => {
+	const cwd = temporaryDirectory();
+	const conf = new Conf({cwd});
+
+	// Set store when no file exists
+	t.notThrows(() => {
+		conf.store = {foo: 'bar'};
+	});
+
+	t.is(conf.get('foo'), 'bar');
+});
+
+test('migrations - should preserve internal data without dot notation access', t => {
+	const cwd = temporaryDirectory();
+
+	const conf = new Conf({
+		cwd,
+		projectVersion: '1.0.0',
+		accessPropertiesByDotNotation: false,
+		migrations: {
+			'1.0.0'(store) {
+				store.set('migrated', true);
+			},
+		},
+	});
+
+	const internal = conf.get('__internal__') as any; // eslint-disable-line @typescript-eslint/no-unsafe-assignment
+	t.is(internal.migrations.version, '1.0.0');
+
+	// Overwrite store
+	conf.store = {newData: 'test'};
+
+	// Internal data should still be preserved
+	const internal2 = conf.get('__internal__') as any; // eslint-disable-line @typescript-eslint/no-unsafe-assignment
+	t.is(internal2.migrations.version, '1.0.0');
+});