Refactor function invocation generation

src/substrait/sql/extended_expression.py

@@ -93,26 +93,32 @@ def expression_from_sqlglot(self, sqlglot_node):
         return self._parse_expression(sqlglot_node)
 
     def _parse_expression(self, expr):
+        """Parse a SQLGlot node and return a Substrait expression.
+
+        This is the internal implementation, expected to be
+        invoked in a recursive manner to parse the whole
+        expression tree.
+        """
         if isinstance(expr, sqlglot.expressions.Literal):
             if expr.is_string:
                 return ParsedSubstraitExpression(
-                    f"literal_{next(self._counter)}",
+                    f"literal${next(self._counter)}",
                     proto.Type(string=proto.Type.String()),
                     proto.Expression(
                         literal=proto.Expression.Literal(string=expr.text)
                     ),
                 )
             elif expr.is_int:
                 return ParsedSubstraitExpression(
-                    f"literal_{next(self._counter)}",
+                    f"literal${next(self._counter)}",
                     proto.Type(i32=proto.Type.I32()),
                     proto.Expression(
                         literal=proto.Expression.Literal(i32=int(expr.name))
                     ),
                 )
             elif sqlglot.helper.is_float(expr.name):
                 return ParsedSubstraitExpression(
-                    f"literal_{next(self._counter)}",
+                    f"literal${next(self._counter)}",
                     proto.Type(fp32=proto.Type.FP32()),
                     proto.Expression(
                         literal=proto.Expression.Literal(float=float(expr.name))
@@ -144,11 +150,7 @@ def _parse_expression(self, expr):
             argument_parsed_expr = self._parse_expression(expr.this)
             function_name = SQL_UNARY_FUNCTIONS[expr.key]
             signature, result_type, function_expression = (
-                self._parse_function_invokation(
-                    function_name,
-                    argument_parsed_expr.type,
-                    argument_parsed_expr.expression,
-                )
+                self._parse_function_invokation(function_name, argument_parsed_expr)
             )
             result_name = f"{function_name}_{argument_parsed_expr.output_name}_{next(self._counter)}"
             return ParsedSubstraitExpression(
@@ -163,11 +165,7 @@ def _parse_expression(self, expr):
             function_name = SQL_BINARY_FUNCTIONS[expr.key]
             signature, result_type, function_expression = (
                 self._parse_function_invokation(
-                    function_name,
-                    left_parsed_expr.type,
-                    left_parsed_expr.expression,
-                    right_parsed_expr.type,
-                    right_parsed_expr.expression,
+                    function_name, left_parsed_expr, right_parsed_expr
                 )
             )
             result_name = f"{function_name}_{left_parsed_expr.output_name}_{right_parsed_expr.output_name}_{next(self._counter)}"
@@ -185,24 +183,27 @@ def _parse_expression(self, expr):
             )
 
     def _parse_function_invokation(
-        self, function_name, left_type, left, right_type=None, right=None
+        self, function_name, argument_parsed_expr, *additional_arguments
     ):
-        binary = False
-        argtypes = [left_type]
-        if right_type or right:
-            binary = True
-            argtypes.append(right_type)
-        signature = self._functions_catalog.signature(function_name, argtypes)
+        """Generates a Substrait function invokation expression.
+
+        The function invocation will be generated from the function name
+        and the arguments as ParsedSubstraitExpression.
+
+        Returns the function signature, the return type and the
+        invokation expression itself.
+        """
+        arguments = [argument_parsed_expr] + list(additional_arguments)
+        signature = self._functions_catalog.signature(
+            function_name, proto_argtypes=[arg.type for arg in arguments]
+        )
 
         try:
             function_anchor = self._functions_catalog.function_anchor(signature)
         except KeyError:
             # No function found with the exact types, try any1_any1 version
             # TODO: What about cases like i32_any1? What about any instead of any1?
-            if binary:
-                signature = f"{function_name}:any1_any1"
-            else:
-                signature = f"{function_name}:any1"
+            signature = f"{function_name}:{'_'.join(['any1']*len(arguments))}"
             function_anchor = self._functions_catalog.function_anchor(signature)
 
         function_return_type = self._functions_catalog.function_return_type(signature)
@@ -216,20 +217,25 @@ def _parse_function_invokation(
             proto.Expression(
                 scalar_function=proto.Expression.ScalarFunction(
                     function_reference=function_anchor,
-                    arguments=(
-                        [
-                            proto.FunctionArgument(value=left),
-                            proto.FunctionArgument(value=right),
-                        ]
-                        if binary
-                        else [proto.FunctionArgument(value=left)]
-                    ),
+                    arguments=[
+                        proto.FunctionArgument(value=arg.expression)
+                        for arg in arguments
+                    ],
                 )
             ),
         )
 
 
 class ParsedSubstraitExpression:
+    """A Substrait expression that was parsed from a SQLGlot node.
+
+    This stores the expression itself, with an associated output name
+    in case it is required to emit projections.
+
+    It also stores the type of the expression (i64, string, boolean, etc...)
+    and the functions that the expression in going to invoke.
+    """
+
     def __init__(self, output_name, type, expression, invoked_functions=None):
         self.expression = expression
         self.output_name = output_name