[uart] Validate parity and stop bits correctly (#20161)

esphome/components/uart/__init__.py

@@ -489,7 +489,8 @@ def final_validate_device_schema(
         return value
 
     def validate_stop_bits(value):
-        if value != stop_bits:
+        # usb_uart channels store stop bits as strings ("1", "1.5", "2").
+        if float(value) != stop_bits:
             raise cv.Invalid(
                 f"Component {name} requires {stop_bits} stop bits for the uart referenced by {uart_bus}"
             )

esphome/components/usb_uart/usb_uart.h

@@ -155,7 +155,22 @@ class USBUartChannelBase : public uart::UARTComponent, public Parented<USBUartCo
   // Re-apply the current line settings (baud, parity, etc) to this already-open channel.
   void load_settings(bool dump_config) override;
   using UARTComponent::load_settings;  // also bring in the no-arg overload for convenience
-  void set_parity(UARTParityOptions parity) { this->parity_ = parity; }
+  void set_parity(UARTParityOptions parity) {
+    this->parity_ = parity;
+    // Keep the base-class parity in sync so uart::UARTComponent::get_parity() reports the configured value.
+    // MARK/SPACE have no uart:: equivalent and report as NONE.
+    switch (parity) {
+      case UART_CONFIG_PARITY_EVEN:
+        uart::UARTComponent::set_parity(uart::UART_CONFIG_PARITY_EVEN);
+        break;
+      case UART_CONFIG_PARITY_ODD:
+        uart::UARTComponent::set_parity(uart::UART_CONFIG_PARITY_ODD);
+        break;
+      default:
+        uart::UARTComponent::set_parity(uart::UART_CONFIG_PARITY_NONE);
+        break;
+    }
+  }
   void set_debug(bool debug) { this->debug_ = debug; }
   void set_dummy_receiver(bool dummy_receiver) { this->dummy_receiver_ = dummy_receiver; }
   void set_debug_prefix(const char *prefix) { this->debug_prefix_ = StringRef(prefix); }

tests/component_tests/uart/test_final_validate.py

@@ -0,0 +1,46 @@
+"""Tests for final validation of UART device requirements against usb_uart channels."""
+
+from pathlib import Path
+
+import pytest
+
+from esphome import config, yaml_util
+from esphome.core import CORE
+
+USB_UART_CONFIG = """
+esphome:
+  name: usb-uart-final-validate
+esp32:
+  variant: esp32s3
+  framework:
+    type: esp-idf
+usb_uart:
+  - type: ch340
+    channels:
+      - id: meter_uart
+        baud_rate: 1200
+        stop_bits: {stop_bits}
+sensor:
+  - platform: kamstrup_kmp
+    uart_id: meter_uart
+    heat_energy:
+      name: Heat energy
+"""
+
+
+@pytest.mark.parametrize(
+    ("stop_bits", "valid"), [("2", True), ("1", False), ("1.5", False)]
+)
+def test_stop_bits_requirement_on_usb_uart_channel(
+    stop_bits: str, valid: bool, tmp_path: Path
+) -> None:
+    """usb_uart stores stop bits as strings; they must still satisfy a numeric requirement."""
+    path = tmp_path / "usb_uart.yaml"
+    path.write_text(USB_UART_CONFIG.format(stop_bits=stop_bits), encoding="utf-8")
+    CORE.config_path = path
+    result = config.validate_config(yaml_util.load_yaml(path), {})
+    errors = [str(err) for err in result.errors]
+    if valid:
+        assert errors == []
+    else:
+        assert any("requires 2 stop bits" in err for err in errors), errors