fix: clamp harmony inversion to valid range when quality changes

tests/ui/timelines/harmony/test_harmony_ui.py

@@ -23,6 +23,28 @@ def test_right_click(self, tlui):
         exec_mock.assert_called_once()
 
 
+class TestInversionClamp:
+    def test_letter_symbol_does_not_crash_when_quality_loses_inversion(self, tlui):
+        harmony, _ = tlui.create_harmony(0, quality="dominant-seventh", inversion=3)
+        tlui.timeline.set_component_data(harmony.id, "quality", "major")
+        # Pre-fix: music21.chord.ChordException — no 3rd inversion on triad.
+        _ = tlui.get_element(harmony.id).letter_symbol
+
+    def test_roman_numeral_label_does_not_crash_when_quality_loses_inversion(
+        self, tlui
+    ):
+        harmony, _ = tlui.create_harmony(0, quality="dominant-seventh", inversion=3)
+        tlui.timeline.set_component_data(harmony.id, "quality", "major")
+        _ = tlui.get_element(harmony.id).roman_numeral_label
+
+    def test_letter_symbol_label_omits_dropped_inversion(self, tlui):
+        harmony, _ = tlui.create_harmony(0, quality="dominant-seventh", inversion=3)
+        tlui.timeline.set_component_data(harmony.id, "quality", "major")
+        # Major triad max inversion is 2, so the 3rd-inversion suffix
+        # (INVERSION_TO_INTERVAL[3] == 7) must not appear in the label.
+        assert "/&7" not in tlui.get_element(harmony.id).letter_symbol_label
+
+
 class TestCopyPaste:
     def test_paste_single_into_timeline(self, tlui, tilia_state):
         _, hui = tlui.create_harmony(0)

tilia/ui/timelines/harmony/elements/harmony.py

@@ -7,6 +7,7 @@
 from PySide6.QtWidgets import QGraphicsItem, QGraphicsTextItem
 
 from tilia.requests import Get, Post, get, post
+from tilia.timelines.harmony.constants import get_inversion_amount
 from tilia.ui.coords import time_x_converter
 from tilia.ui.timelines.base.element import TimelineUIElement
 from tilia.ui.timelines.drag import DragManager
@@ -69,6 +70,13 @@ def font_type(self):
     def key(self):
         return self.timeline_ui.get_key_by_time(self.get_data("time"))
 
+    @property
+    def clamped_inversion(self):
+        return min(
+            self.get_data("inversion"),
+            get_inversion_amount(self.get_data("quality")),
+        )
+
     @property
     def letter_symbol(self):
         symbol = music21.harmony.ChordSymbol(
@@ -78,7 +86,7 @@ def letter_symbol(self):
                 self.get_data("accidental"),
             )
             + QUALITY_TO_ABBREVIATION[self.get_data("quality")],
-            inversion=self.get_data("inversion"),
+            inversion=self.clamped_inversion,
         )
         applied_to = self.get_data("applied_to")
         if applied_to:
@@ -119,7 +127,7 @@ def roman_numeral_label(self):
             self.get_data("quality"),
             self.key,
             self.get_data("applied_to"),
-            self.get_data("inversion"),
+            self.clamped_inversion,
         )
 
     @property
@@ -150,7 +158,7 @@ def letter_symbol_label(self):
             case 2:
                 figure = figure.replace("##", "`#`#")
 
-        if inversion := self.get_data("inversion"):
+        if inversion := self.clamped_inversion:
             # bass_step = harmony.calculate.bass_step(self.get_data('step'), inversion)
             # figure += '/' + INT_TO_NOTE_NAME[bass_step]  # TODO calculate bass note
             figure += "/&" + str(INVERSION_TO_INTERVAL[inversion])