Error when both --erase and --format are specified in flash

Author: Copilot

mpflash/cli_flash.py

@@ -270,6 +270,10 @@ def _create_worklist_or_fail(*create_args, **create_kwargs) -> FlashTaskList:
     params.bootloader = BootloaderMethod(params.bootloader)
     reflash_commands: List[str] = []
 
+    # --erase and --format are mutually exclusive; only one makes sense at a time.
+    if params.erase and params.format_fs:
+        raise click.UsageError("--erase and --format cannot be used together; specify only one.")
+
     # make it simple for the user to flash one board by asking for the serial port if not specified
     if params.boards == ["?"] or params.serial == "?":  #  or params.variant == "?":
         params.serial = ["?"]

tests/cli/test_cli_flash.py

@@ -210,6 +210,22 @@ def test_mpflash_flash_no_matching_serial_ports_returns_usage_error(mocker: Mock
     assert "No serial ports matched" in result.output
 
 
+def test_mpflash_flash_erase_and_format_are_mutually_exclusive(mocker: MockerFixture):
+    """Reject using --erase and --format together with a user-friendly error."""
+    args = ["flash", "--board", "RPI_PICO2", "--serial", "COM8", "--erase", "--format"]
+
+    mocker.patch(
+        "mpflash.ask_input.ask_missing_params",
+        Mock(side_effect=fake_ask_missing_params),
+    )
+
+    runner = CliRunner()
+    result = runner.invoke(cli_main.cli, args, standalone_mode=True)
+
+    assert result.exit_code == 2
+    assert "--erase and --format cannot be used together" in result.output
+
+
 def test_mpflash_flash_format_option_passed_to_flash_tasks(mocker: MockerFixture):
     """The --format flag is forwarded to flash_tasks as format_fs=True."""
     args = ["flash", "--board", "RPI_PICO2", "--serial", "COM8", "--volume", "D:\\", "--format"]