fix(shaclgen): emit sh:minCount/maxCount 0 for zero cardinality values

The SHACL generator used Python truthiness checks for
minimum_cardinality and maximum_cardinality:

    if s.minimum_cardinality:  # 0 is falsy!
    if s.maximum_cardinality:  # 0 is falsy!

Since int(0) evaluates as False in Python, setting
maximum_cardinality: 0 (which should produce sh:maxCount 0,
meaning the property MUST NOT appear) silently emitted nothing.

This patch changes both checks to explicit `is not None`
comparisons, matching the pattern already used in the OWL
generator (owlgen.py lines 627-640) for the same attributes.

sh:maxCount 0 is valid per the W3C SHACL specification and means
"this property must not exist on any conforming node". This is
the standard mechanism for suppressing inherited properties on
subclasses via slot_usage with maximum_cardinality: 0.

Signed-off-by: Carlo van Driesten <carlo.van-driesten@bmw.de>

Author: jdsika

packages/linkml/src/linkml/generators/shaclgen.py

@@ -169,7 +169,7 @@ def prop_pv_literal(p, v):
                 prop_pv_literal(SH.name, s.title)
                 prop_pv_literal(SH.description, s.description)
                 # minCount
-                if s.minimum_cardinality:
+                if s.minimum_cardinality is not None:
                     prop_pv_literal(SH.minCount, s.minimum_cardinality)
                 elif s.exact_cardinality:
                     prop_pv_literal(SH.minCount, s.exact_cardinality)
@@ -179,7 +179,7 @@ def prop_pv_literal(p, v):
                 elif s.required and not s.identifier:
                     prop_pv_literal(SH.minCount, 1)
                 # maxCount
-                if s.maximum_cardinality:
+                if s.maximum_cardinality is not None:
                     prop_pv_literal(SH.maxCount, s.maximum_cardinality)
                 elif s.exact_cardinality:
                     prop_pv_literal(SH.maxCount, s.exact_cardinality)

tests/linkml/test_generators/input/shaclgen/cardinality.yaml

@@ -17,6 +17,17 @@ classes:
     slots:
       - list_exact_size
 
+  ParentClass:
+    slots:
+      - inherited_slot
+      - restricted_slot
+
+  ChildWithZeroMaxCard:
+    is_a: ParentClass
+    slot_usage:
+      restricted_slot:
+        maximum_cardinality: 0
+
 slots:
   list_min_max_size:
     range: integer
@@ -28,3 +39,11 @@ slots:
     range: integer
     multivalued: true
     exact_cardinality: 3
+
+  inherited_slot:
+    range: string
+    multivalued: true
+
+  restricted_slot:
+    range: string
+    multivalued: true

tests/linkml/test_generators/test_shaclgen.py

@@ -568,6 +568,46 @@ def test_multivalued_slot_exact_cardinality(input_path):
     ) in g
 
 
+def test_zero_maximum_cardinality_emits_maxcount(input_path):
+    """Test that maximum_cardinality: 0 correctly emits sh:maxCount 0.
+
+    Regression test for the bug where Python truthiness check
+    `if s.maximum_cardinality:` would skip the value 0 (falsy),
+    failing to emit sh:maxCount 0 in the generated SHACL shape.
+    The fix uses `if s.maximum_cardinality is not None:` instead.
+
+    This is the primary mechanism for suppressing inherited slots on
+    subclasses via slot_usage (e.g., OWL maxCardinality 0 pattern).
+    """
+    shacl = ShaclGenerator(input_path("shaclgen/cardinality.yaml"), mergeimports=True).serialize()
+
+    g = rdflib.Graph()
+    g.parse(data=shacl)
+
+    # Find the ChildWithZeroMaxCard shape
+    child_uri = URIRef("https://w3id.org/linkml/examples/cardinality/ChildWithZeroMaxCard")
+    restricted_slot_uri = URIRef("https://w3id.org/linkml/examples/cardinality/restricted_slot")
+
+    # Get all property shapes for the child class
+    prop_nodes = list(g.objects(child_uri, SH.property))
+    assert prop_nodes, "ChildWithZeroMaxCard should have property shapes"
+
+    # Find the property shape for restricted_slot
+    restricted_prop_node = None
+    for pn in prop_nodes:
+        if (pn, SH.path, restricted_slot_uri) in g:
+            restricted_prop_node = pn
+            break
+    assert restricted_prop_node is not None, "Should have a property shape for restricted_slot"
+
+    # The critical assertion: sh:maxCount 0 must be emitted
+    max_count_values = list(g.objects(restricted_prop_node, SH.maxCount))
+    assert len(max_count_values) == 1, f"Expected exactly one sh:maxCount, got {max_count_values}"
+    assert max_count_values[0] == rdflib.term.Literal(
+        0, datatype=rdflib.term.URIRef("http://www.w3.org/2001/XMLSchema#integer")
+    ), f"sh:maxCount should be 0, got {max_count_values[0]}"
+
+
 def test_exclude_imports(input_path):
     shacl = ShaclGenerator(
         input_path("shaclgen/exclude_imports.yaml"), mergeimports=True, exclude_imports=True