fix: handle localized duplicate-database errors on restart (#13) (#15)

`pg0 start` failed to restart an existing instance when PostgreSQL
returned a localized duplicate-database error (e.g. on Windows with a
Chinese locale: `数据库 "x" 已经存在`). The previous logic relied on the
English substring `already exists` to swallow the error, which never
matched on non-English builds.

Replaced the post-hoc string match with a `database_exists()` pre-check
so the create path is locale-independent, and added a Python regression
test that starts → stops → restarts an instance with a custom database.

Author: nicoloboschi

sdk/python/tests/test_pg0.py

@@ -152,6 +152,29 @@ def test_port_conflict_error(self, clean_instance):
             pg2.stop()
             pg0.drop(f"{TEST_NAME}-2")
 
+    def test_restart_with_custom_database(self, clean_instance):
+        """Restarting an instance with a non-default database must be idempotent.
+
+        Regression test for https://github.com/vectorize-io/pg0/issues/13
+        Previously, the second start failed because pg0 only matched the English
+        substring "already exists" when CREATE DATABASE returned a duplicate
+        error, so restarts on PostgreSQL builds with a non-English lc_messages
+        (e.g. Chinese on Windows: `数据库 "x" 已经存在`) crashed startup.
+        """
+        pg = Pg0(name=TEST_NAME, port=TEST_PORT, database="testdb")
+        pg.start()
+        pg.execute("CREATE TABLE restart_test (id int);")
+        pg.execute("INSERT INTO restart_test VALUES (42);")
+        pg.stop()
+
+        # Second start must succeed and preserve data
+        info = pg.start()
+        assert info.running is True
+        assert "testdb" in info.uri
+        result = pg.execute("SELECT id FROM restart_test;")
+        assert "42" in result
+        pg.stop()
+
     @pytest.mark.skipif(
         sys.platform == "win32",
         reason="signal.SIGKILL does not exist on Windows; crash-recovery behavior is exercised by the Unix matrix.",

src/main.rs

@@ -893,13 +893,12 @@ fn start(
 
     // Create the database if it doesn't exist and it's not the default 'postgres'
     if database != "postgres" {
-        println!("Creating database '{}'...", database);
-        if let Err(e) = postgresql.create_database(&database) {
-            // Ignore error if database already exists
-            let err_str = e.to_string();
-            if !err_str.contains("already exists") {
-                return Err(e.into());
-            }
+        // Pre-check existence rather than relying on the duplicate-database error
+        // string, which is localized by PostgreSQL's lc_messages (e.g. on Windows
+        // with a Chinese locale: `数据库 "x" 已经存在`). See vectorize-io/pg0#13.
+        if !postgresql.database_exists(&database)? {
+            println!("Creating database '{}'...", database);
+            postgresql.create_database(&database)?;
         }
         // Grant privileges to the user on the database
         if username != "postgres" {