fix(api): ensure that round behavior is consistent across backends

BREAKING CHANGE: The `round` method no longer accepts arbitrary integer expressions for the number of digits to round to; the value must be a Python integer value.

ibis/backends/polars/compiler.py

@@ -638,7 +638,7 @@ def round(op, **kw):
     arg = translate(op.arg, **kw)
     typ = PolarsType.from_ibis(op.dtype)
     digits = _literal_value(op.digits)
-    return arg.round(digits or 0).cast(typ)
+    return arg.round(digits).cast(typ)
 
 
 @translate.register(ops.Radians)

ibis/backends/sql/compilers/datafusion.py

@@ -533,5 +533,8 @@ def visit_ArrayFlatten(self, op, *, arg):
     def visit_RandomUUID(self, op, **kw):
         return self.f.anon.uuid()
 
+    def visit_Round(self, op, *, arg, digits):
+        return self.cast(self.f.round(arg, digits), op.dtype)
+
 
 compiler = DataFusionCompiler()

ibis/backends/sql/compilers/druid.py

@@ -196,5 +196,8 @@ def visit_TimestampFromYMDHMS(
             )
         )
 
+    def visit_Round(self, op, *, arg, digits):
+        return self.cast(self.f.round(arg, digits), op.dtype)
+
 
 compiler = DruidCompiler()

ibis/backends/sql/compilers/duckdb.py

@@ -712,5 +712,8 @@ def visit_TableUnnest(
     def visit_StringToTime(self, op, *, arg, format_str):
         return self.cast(self.f.str_to_time(arg, format_str), to=dt.time)
 
+    def visit_Round(self, op, *, arg, digits):
+        return self.cast(self.f.round(arg, digits), op.dtype)
+
 
 compiler = DuckDBCompiler()

ibis/backends/sql/compilers/sqlite.py

@@ -537,5 +537,8 @@ def visit_DateDelta(self, op, *, left, right, part):
             )
         return self.f._ibis_date_delta(left, right)
 
+    def visit_Round(self, op, *, arg, digits):
+        return self.cast(self.f.round(arg, digits), op.dtype)
+
 
 compiler = SQLiteCompiler()

ibis/backends/sql/compilers/trino.py

@@ -692,5 +692,8 @@ def visit_ArraySum(self, op, *, arg):
     def visit_ArrayMean(self, op, *, arg):
         return self.visit_ArraySumAgg(op, arg=arg, output=operator.truediv)
 
+    def visit_Round(self, op, *, arg, digits):
+        return self.cast(self.f.round(arg, digits), op.dtype)
+
 
 compiler = TrinoCompiler()

ibis/backends/tests/test_numeric.py

@@ -1516,3 +1516,25 @@ def test_bitwise_not_col(backend, alltypes, df):
     result = expr.execute()
     expected = ~df.int_col
     backend.assert_series_equal(result, expected.rename("tmp"))
+
+
+def test_column_round_is_integer(con):
+    t = ibis.memtable({"x": [1.2, 3.4]})
+    expr = t.x.round().cast(int)
+    result = con.execute(expr)
+
+    one, three = sorted(result.tolist())
+
+    assert one == 1
+    assert isinstance(one, int)
+
+    assert three == 3
+    assert isinstance(three, int)
+
+
+def test_scalar_round_is_integer(con):
+    expr = ibis.literal(1.2).round().cast(int)
+    result = con.execute(expr)
+
+    assert result == 1
+    assert isinstance(result, int)

ibis/expr/operations/numeric.py

@@ -148,19 +148,24 @@ class Round(Value):
     """Round a value."""
 
     arg: StrictNumeric
-    # TODO(kszucs): the default should be 0 instead of being None
-    digits: Optional[Integer] = None
+    digits: int = 0
 
     shape = rlz.shape_like("arg")
 
     @property
     def dtype(self):
-        if self.arg.dtype.is_decimal():
-            return self.arg.dtype
-        elif self.digits is None:
-            return dt.int64
-        else:
-            return dt.double
+        digits = self.digits
+        arg_dtype = self.arg.dtype
+
+        if arg_dtype.is_decimal():
+            return arg_dtype.copy(scale=digits)
+
+        nullable = arg_dtype.nullable
+
+        if not digits:
+            return dt.int64.copy(nullable=nullable)
+
+        return dt.double.copy(nullable=nullable)
 
 
 @public

ibis/expr/types/numeric.py

@@ -56,7 +56,7 @@ def __neg__(self) -> NumericValue:
         """
         return self.negate()
 
-    def round(self, digits: int | IntegerValue | None = None) -> NumericValue:
+    def round(self, digits: int = 0) -> NumericValue:
         """Round values to an indicated number of decimal places.
 
         Parameters

ibis/tests/expr/test_sql_builtins.py

@@ -148,11 +148,11 @@ def test_sign(functional_alltypes, lineitem):
 def test_round(functional_alltypes, lineitem):
     result = functional_alltypes.double_col.round()
     assert isinstance(result, ir.IntegerColumn)
-    assert result.op().args[1] is None
+    assert result.op().args[1] == 0
 
     result = functional_alltypes.double_col.round(2)
     assert isinstance(result, ir.FloatingColumn)
-    assert result.op().args[1] == ibis.literal(2).op()
+    assert result.op().args[1] == 2
 
     # Even integers are double (at least in Impala, check with other DB
     # implementations)