feat: add ops.Cast to translator and decompiler

Author: gforsyth

ibis_substrait/compiler/decompile.py

@@ -765,6 +765,15 @@ def decompile_singular_or_list(
     ) -> ir.ValueExpr:
         return decompile(singular_or_list, children, offsets, decompiler)
 
+    @staticmethod
+    def decompile_cast(
+        cast: stalg.Expression.Cast,
+        children: Sequence[ir.TableExpr],
+        offsets: Sequence[int],
+        decompiler: SubstraitDecompiler,
+    ) -> ir.ValueExpr:
+        return decompile(cast, children, offsets, decompiler)
+
 
 @decompile.register
 def _decompile_expression(
@@ -874,6 +883,17 @@ def _decompile_expression_singular_or_list(
     )
 
 
+@decompile.register
+def _decompile_expression_cast(
+    msg: stalg.Expression.Cast,
+    children: Sequence[ir.TableExpr],
+    field_offsets: Sequence[int],
+    decompiler: SubstraitDecompiler,
+) -> ir.ValueExpr:
+    column = decompile(msg.input, children, field_offsets, decompiler)
+    return column.cast(_decompile_type(msg.type))
+
+
 class LiteralDecompiler:
     @staticmethod
     def decompile_boolean(value: bool) -> tuple[bool, dt.Boolean]:

ibis_substrait/compiler/mapping.py

@@ -3,7 +3,6 @@
     "And": "and",
     "Any": "any",
     "Between": "between",
-    "Cast": "cast",
     "Count": "count",
     "CountDistinct": "countdistinct",
     "Divide": "/",  # wrong but using for duckdb compatibility right now

ibis_substrait/compiler/translate.py

@@ -943,3 +943,17 @@ def _contains(
             options=[translate(value, compiler, **kwargs) for value in op.options],
         )
     )
+
+
+@translate.register(ops.Cast)
+def _cast(
+    op: ops.Cast,
+    expr: ir.TableExpr,
+    compiler: SubstraitCompiler,
+    **kwargs: Any,
+) -> stalg.Expression:
+    return stalg.Expression(
+        cast=stalg.Expression.Cast(
+            type=translate(op.to), input=translate(op.arg, compiler, **kwargs)
+        )
+    )

ibis_substrait/tests/compiler/test_decompiler.py

@@ -238,3 +238,11 @@ def test_singular_or_list(compiler):
     plan = compiler.compile(expr)
     (result,) = decompile(plan)
     assert result.equals(expr)
+
+
+def test_cast(compiler):
+    t = ibis.table([("bork32", dt.float32)], name="t")
+    expr = t[t.bork32.cast("float64").name("bork64")]
+    plan = compiler.compile(expr)
+    (result,) = decompile(plan)
+    assert result.equals(expr)