fix: only greet once when setting the same mode (#301)

With this fix, ``Emitter.set_mode(mode)`` becomes a no-op if the emitter is
already at that ``mode``. This scenario can happen, for example, if the Emitter
is initialized with a mode and then the Dispatcher sets the same mode during
command-line handling.

craft_cli/messages.py

@@ -510,6 +510,9 @@ def get_mode(self) -> EmitterMode:
     @_active_guard()
     def set_mode(self, mode: EmitterMode) -> None:
         """Set the mode of the emitter."""
+        if mode == self._mode:
+            return
+
         self._mode = mode
         self._log_handler.mode = mode
 

docs/changelog.rst

@@ -7,6 +7,12 @@ Changelog
 See the `Releases page`_ on GitHub for a complete list of commits that are
 included in each version.
 
+2.10.1 (2024-Nov-11)
+--------------------
+
+- Fix an issue where setting an ``Emitter`` to the same mode multiple times
+  resulted in multiple greetings.
+
 2.10.0 (2024-Oct-31)
 --------------------
 - Support adding a link to documentation in help messages.

tests/unit/test_messages_emitter.py

@@ -18,6 +18,7 @@
 
 import logging
 import sys
+from unittest import mock
 from unittest.mock import call, patch
 
 import pytest
@@ -298,6 +299,32 @@ def test_set_mode_developer_modes(get_initiated_emitter, mode):
     assert handler.mode == mode
 
 
+@pytest.mark.parametrize(
+    "mode",
+    [
+        EmitterMode.VERBOSE,
+        EmitterMode.DEBUG,
+        EmitterMode.TRACE,
+    ],
+)
+def test_set_mode_repeated(get_initiated_emitter, mode):
+    """Repeatedly setting the same mode should not emit multiple greetings."""
+    greeting = "greeting"
+    emitter = get_initiated_emitter(EmitterMode.QUIET, greeting=greeting)
+
+    emitter.set_mode(mode)
+    emitter.set_mode(mode)
+
+    log_locat = f"Logging execution to {emitter._log_filepath!r}"
+    extra_print_args = {"use_timestamp": mock.ANY, "avoid_logging": True, "end_line": True}
+
+    # Only a single printing of the greeting and the logpath
+    assert emitter.printer_calls == [
+        call().show(sys.stderr, greeting, **extra_print_args),
+        call().show(sys.stderr, log_locat, **extra_print_args),
+    ]
+
+
 # -- tests for emitting messages of all kind