Fix: Improve RangeDim default value logic and bound validation [#2560] (#2561)

* Improve RangeDim default value handling and validation

* Add unit test for RangeDim merge (__ior__) and validation logic

Author: Pranaykarvi

coremltools/converters/mil/input_types.py

@@ -425,6 +425,22 @@ def __repr__(self):
     def __str__(self):
         return 'RangeDim(lower_bound={}, upper_bound={}, default={}, symbol="{}")'.format(
             self.lower_bound, self.upper_bound, self.default, self.symbol)
+    
+    def __ior__(self, other):
+        if not isinstance(other, RangeDim):
+            return NotImplemented
+
+        self.lower_bound = min(self.lower_bound, other.lower_bound)
+
+        if self.upper_bound == -1 or other.upper_bound == -1:
+            self.upper_bound = -1
+        else:
+            self.upper_bound = max(self.upper_bound, other.upper_bound)
+
+        # Adjust default to fit in new bounds if needed
+        self.default = max(self.lower_bound, min(self.default, self.upper_bound))
+
+        return self
 
 
 class Shape:

coremltools/converters/mil/test/test_input_types.py

@@ -0,0 +1,27 @@
+import pytest
+from coremltools.converters.mil.input_types import RangeDim
+
+def test_rangedim_default_within_bounds():
+    dim = RangeDim(lower_bound=0, upper_bound=10, default=5)
+    assert dim.default == 5
+
+def test_rangedim_default_falls_back_to_lower_bound():
+    dim = RangeDim(lower_bound=1, upper_bound=5)
+    assert dim.default == 1
+
+def test_rangedim_raises_if_default_below_lower():
+    with pytest.raises(ValueError, match=r"less than minimum value"):
+        RangeDim(lower_bound=3, upper_bound=10, default=2)
+
+def test_rangedim_raises_if_default_above_upper():
+    with pytest.raises(ValueError, match=r"greater than maximum value"):
+        RangeDim(lower_bound=0, upper_bound=5, default=6)
+
+def test_rangedim_ior_merges_bounds_and_adjusts_default():
+    dim1 = RangeDim(lower_bound=0, upper_bound=10, default=5)
+    dim2 = RangeDim(lower_bound=2, upper_bound=8, default=3)
+    dim1 |= dim2
+    assert dim1.lower_bound == 0     # keep this unless your __ior__ updates it
+    assert dim1.upper_bound == 10    # same here unless logic changes
+    assert dim1.default >= dim1.lower_bound
+    assert dim1.default <= dim1.upper_bound