fix: ak.argcombinations should allow negative axis (#3301)

* fix: ak.argcombinations should allow negative axis

* fix: ak.argcombinations should allow negative axis

src/awkward/operations/ak_argcombinations.py

@@ -108,20 +108,17 @@ def _impl(
 
     axis = regularize_axis(axis, none_allowed=False)
 
-    if axis < 0:
-        raise ValueError("the 'axis' for argcombinations must be non-negative")
-    else:
-        with HighLevelContext(behavior=behavior, attrs=attrs) as ctx:
-            layout = ak._do.local_index(
-                ctx.unwrap(array, allow_record=False, primitive_policy="error"),
-                axis,
-            )
-        out = ak._do.combinations(
-            layout,
-            n,
-            replacement=replacement,
-            axis=axis,
-            fields=fields,
-            parameters=parameters,
+    with HighLevelContext(behavior=behavior, attrs=attrs) as ctx:
+        layout = ak._do.local_index(
+            ctx.unwrap(array, allow_record=False, primitive_policy="error"),
+            axis,
         )
-        return ctx.wrap(out, highlevel=highlevel)
+    out = ak._do.combinations(
+        layout,
+        n,
+        replacement=replacement,
+        axis=axis,
+        fields=fields,
+        parameters=parameters,
+    )
+    return ctx.wrap(out, highlevel=highlevel)

tests/test_3300_allow_negative_axis_in_argcombinations.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+import awkward as ak
+
+
+def test():
+    array = ak.Array([[0.0, 1.1, 2.2], [], [3.3, 4.4], [5.5], [6.6, 7.7, 8.8, 9.9]])
+
+    assert ak.combinations(array, 2, axis=-1).tolist() == [
+        [(0.0, 1.1), (0.0, 2.2), (1.1, 2.2)],
+        [],
+        [(3.3, 4.4)],
+        [],
+        [(6.6, 7.7), (6.6, 8.8), (6.6, 9.9), (7.7, 8.8), (7.7, 9.9), (8.8, 9.9)],
+    ]
+    assert ak.argcombinations(array, 2, axis=-1).tolist() == [
+        [(0, 1), (0, 2), (1, 2)],
+        [],
+        [(0, 1)],
+        [],
+        [(0, 1), (0, 2), (0, 3), (1, 2), (1, 3), (2, 3)],
+    ]