improve postgres support

db/db.go

@@ -119,6 +119,54 @@ func normalizeDriver(driver string) string {
 	}
 }
 
+// ResolveDriver determines the effective database driver.
+// If driver is unset and DSN looks like PostgreSQL, it infers postgres.
+func ResolveDriver(configuredDriver, dsn string) (driver string, inferredFromDSN bool, err error) {
+	normalized := strings.ToLower(strings.TrimSpace(configuredDriver))
+	switch normalized {
+	case "sqlite3":
+		normalized = "sqlite"
+	case "postgresql":
+		normalized = "postgres"
+	}
+
+	if normalized == "" {
+		if looksLikePostgresDSN(dsn) {
+			return "postgres", true, nil
+		}
+		return "sqlite", false, nil
+	}
+
+	if normalized == "sqlite" && looksLikePostgresDSN(dsn) {
+		return "", false, fmt.Errorf("database_driver is sqlite but database_url looks like a postgres DSN; set settings.database_driver=postgres")
+	}
+
+	return normalized, false, nil
+}
+
+func looksLikePostgresDSN(dsn string) bool {
+	trimmed := strings.ToLower(strings.TrimSpace(dsn))
+	if trimmed == "" {
+		return false
+	}
+	if strings.HasPrefix(trimmed, "postgres://") || strings.HasPrefix(trimmed, "postgresql://") {
+		return true
+	}
+
+	// Also support key=value style PostgreSQL DSNs.
+	if strings.Contains(trimmed, "=") {
+		hasHost := strings.Contains(trimmed, "host=")
+		hasUser := strings.Contains(trimmed, "user=")
+		hasDB := strings.Contains(trimmed, "dbname=")
+		hasSSL := strings.Contains(trimmed, "sslmode=")
+		if (hasHost && hasUser) || (hasHost && hasDB) || (hasUser && hasDB) || (hasHost && hasSSL) {
+			return true
+		}
+	}
+
+	return false
+}
+
 // ConvertToSQLParams is a utility function that generically converts a struct to a corresponding sqlc-generated struct
 func ConvertToSQLParams(input interface{}, output interface{}) {
 	inputVal := reflect.ValueOf(input).Elem()