fix: Set Substrait output types for expressions (#20597)

## Which issue does this PR close?

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- Closes #15831.

## Rationale for this change

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The Substrait producer did not set the ScalarFunction `output_type` when
converting binary expressions, which broke consumers relying on the
`output_type`.

## What changes are included in this PR?

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* Refactor `from_join` and `from_between` to eliminate direct calls to
`make_binary_op_scalar_func`
* Set the Substrait ScalarFunction `output_type` when converting several
types of DataFusion expressions:
  * Binary expressions (`Expr::BinaryExpr`)
  * Unary expressions (like `Expr::Not`)
  * Scalar functions (`Expr::ScalarFunction`)

There are a few more places where the `output_type` has not been set,
such as `from_like` and `from_in_list`, as mentioned in #15831. I've
left these out of scope here as fixing them would require more
substantial code changes.

## Are these changes tested?

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Yes, via a new unit test.

## Are there any user-facing changes?

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No, beyond the Substrait output fix.

Author: wlhjason

datafusion/substrait/src/logical_plan/producer/expr/scalar_function.rs

@@ -15,22 +15,35 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use crate::logical_plan::producer::{SubstraitProducer, to_substrait_literal_expr};
+use crate::logical_plan::producer::{
+    SubstraitProducer, to_substrait_literal_expr, to_substrait_type,
+};
+use datafusion::arrow::datatypes::DataType;
 use datafusion::common::datatype::FieldExt;
 use datafusion::common::{
     DFSchemaRef, ScalarValue, internal_datafusion_err, not_impl_err, substrait_err,
 };
-use datafusion::logical_expr::{Between, BinaryExpr, Expr, Like, Operator, expr};
+use datafusion::logical_expr::{
+    Between, BinaryExpr, Expr, ExprSchemable, Like, Operator, expr,
+};
 use substrait::proto::expression::{RexType, ScalarFunction};
 use substrait::proto::function_argument::ArgType;
-use substrait::proto::{Expression, FunctionArgument};
+use substrait::proto::{Expression, FunctionArgument, Type};
 
 pub fn from_scalar_function(
     producer: &mut impl SubstraitProducer,
     fun: &expr::ScalarFunction,
     schema: &DFSchemaRef,
 ) -> datafusion::common::Result<Expression> {
-    from_function(producer, fun.name(), &fun.args, schema)
+    let (_, output_field) = Expr::ScalarFunction(fun.clone()).to_field(schema)?;
+    from_function(
+        producer,
+        fun.name(),
+        &fun.args,
+        output_field.data_type(),
+        output_field.is_nullable(),
+        schema,
+    )
 }
 
 pub fn from_higher_order_function(
@@ -100,12 +113,20 @@ pub fn from_higher_order_function(
         .collect::<datafusion::common::Result<_>>()?;
 
     let function_anchor = producer.register_function(fun.name().to_string());
+
+    let (_, output_field) = Expr::HigherOrderFunction(fun.clone()).to_field(schema)?;
+    let output_type = to_substrait_type(
+        producer,
+        output_field.data_type(),
+        output_field.is_nullable(),
+    )?;
+
     #[expect(deprecated)]
     Ok(Expression {
         rex_type: Some(RexType::ScalarFunction(ScalarFunction {
             function_reference: function_anchor,
             arguments,
-            output_type: None,
+            output_type: Some(output_type),
             options: vec![],
             args: vec![],
         })),
@@ -116,6 +137,8 @@ fn from_function(
     producer: &mut impl SubstraitProducer,
     name: &str,
     args: &[Expr],
+    output_type: &DataType,
+    output_nullability: bool,
     schema: &DFSchemaRef,
 ) -> datafusion::common::Result<Expression> {
     let mut arguments: Vec<FunctionArgument> = vec![];
@@ -126,14 +149,15 @@ fn from_function(
     }
 
     let arguments = custom_argument_handler(name, arguments);
+    let output_type = to_substrait_type(producer, output_type, output_nullability)?;
 
     let function_anchor = producer.register_function(name.to_string());
     #[expect(deprecated)]
     Ok(Expression {
         rex_type: Some(RexType::ScalarFunction(ScalarFunction {
             function_reference: function_anchor,
             arguments,
-            output_type: None,
+            output_type: Some(output_type),
             options: vec![],
             args: vec![],
         })),
@@ -177,7 +201,13 @@ pub fn from_unary_expr(
         Expr::Negative(arg) => ("negate", arg),
         expr => not_impl_err!("Unsupported expression: {expr:?}")?,
     };
-    to_substrait_unary_scalar_fn(producer, fn_name, arg, schema)
+    let (_, output_field) = expr.to_field(schema)?;
+    let output_type = to_substrait_type(
+        producer,
+        output_field.data_type(),
+        output_field.is_nullable(),
+    )?;
+    to_substrait_unary_scalar_fn(producer, fn_name, arg, schema, &output_type)
 }
 
 pub fn from_binary_expr(
@@ -188,7 +218,19 @@ pub fn from_binary_expr(
     let BinaryExpr { left, op, right } = expr;
     let l = producer.handle_expr(left, schema)?;
     let r = producer.handle_expr(right, schema)?;
-    Ok(make_binary_op_scalar_func(producer, &l, &r, *op))
+    let (_, output_field) = Expr::BinaryExpr(expr.clone()).to_field(schema)?;
+    let output_type = to_substrait_type(
+        producer,
+        output_field.data_type(),
+        output_field.is_nullable(),
+    )?;
+    Ok(make_binary_op_scalar_func(
+        producer,
+        &l,
+        &r,
+        *op,
+        &output_type,
+    ))
 }
 
 pub fn from_like(
@@ -283,6 +325,7 @@ fn to_substrait_unary_scalar_fn(
     fn_name: &str,
     arg: &Expr,
     schema: &DFSchemaRef,
+    output_type: &Type,
 ) -> datafusion::common::Result<Expression> {
     let function_anchor = producer.register_function(fn_name.to_string());
     let substrait_expr = producer.handle_expr(arg, schema)?;
@@ -293,7 +336,7 @@ fn to_substrait_unary_scalar_fn(
             arguments: vec![FunctionArgument {
                 arg_type: Some(ArgType::Value(substrait_expr)),
             }],
-            output_type: None,
+            output_type: Some(output_type.clone()),
             options: vec![],
             ..Default::default()
         })),
@@ -306,6 +349,7 @@ pub fn make_binary_op_scalar_func(
     lhs: &Expression,
     rhs: &Expression,
     op: Operator,
+    output_type: &Type,
 ) -> Expression {
     let function_anchor = producer.register_function(operator_to_name(op).to_string());
     #[expect(deprecated)]
@@ -320,7 +364,7 @@ pub fn make_binary_op_scalar_func(
                     arg_type: Some(ArgType::Value(rhs.clone())),
                 },
             ],
-            output_type: None,
+            output_type: Some(output_type.clone()),
             args: vec![],
             options: vec![],
         })),
@@ -338,57 +382,21 @@ pub fn from_between(
         low,
         high,
     } = between;
-    if *negated {
-        // `expr NOT BETWEEN low AND high` can be translated into (expr < low OR high < expr)
-        let substrait_expr = producer.handle_expr(expr.as_ref(), schema)?;
-        let substrait_low = producer.handle_expr(low.as_ref(), schema)?;
-        let substrait_high = producer.handle_expr(high.as_ref(), schema)?;
-
-        let l_expr = make_binary_op_scalar_func(
-            producer,
-            &substrait_expr,
-            &substrait_low,
-            Operator::Lt,
-        );
-        let r_expr = make_binary_op_scalar_func(
-            producer,
-            &substrait_high,
-            &substrait_expr,
-            Operator::Lt,
-        );
 
-        Ok(make_binary_op_scalar_func(
-            producer,
-            &l_expr,
-            &r_expr,
-            Operator::Or,
-        ))
+    let expr = if *negated {
+        // `expr NOT BETWEEN low AND high` can be translated into (expr < low OR high < expr)
+        Expr::or(
+            Expr::lt(*expr.clone(), *low.clone()),
+            Expr::lt(*high.clone(), *expr.clone()),
+        )
     } else {
         // `expr BETWEEN low AND high` can be translated into (low <= expr AND expr <= high)
-        let substrait_expr = producer.handle_expr(expr.as_ref(), schema)?;
-        let substrait_low = producer.handle_expr(low.as_ref(), schema)?;
-        let substrait_high = producer.handle_expr(high.as_ref(), schema)?;
-
-        let l_expr = make_binary_op_scalar_func(
-            producer,
-            &substrait_low,
-            &substrait_expr,
-            Operator::LtEq,
-        );
-        let r_expr = make_binary_op_scalar_func(
-            producer,
-            &substrait_expr,
-            &substrait_high,
-            Operator::LtEq,
-        );
-
-        Ok(make_binary_op_scalar_func(
-            producer,
-            &l_expr,
-            &r_expr,
-            Operator::And,
-        ))
-    }
+        Expr::and(
+            Expr::lt_eq(*low.clone(), *expr.clone()),
+            Expr::lt_eq(*expr.clone(), *high.clone()),
+        )
+    };
+    producer.handle_expr(&expr, schema)
 }
 
 pub fn operator_to_name(op: Operator) -> &'static str {
@@ -438,3 +446,37 @@ pub fn operator_to_name(op: Operator) -> &'static str {
         Operator::Colon => "colon",
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::logical_plan::producer::{
+        DefaultSubstraitProducer, SubstraitProducer, to_substrait_type,
+    };
+    use datafusion::arrow::datatypes::DataType;
+    use datafusion::common::{DFSchema, DFSchemaRef};
+    use datafusion::execution::SessionStateBuilder;
+    use datafusion::prelude::lit;
+    use substrait::proto::Expression;
+    use substrait::proto::expression::{RexType, ScalarFunction};
+
+    #[tokio::test]
+    async fn binary_expr_output_type() -> datafusion::common::Result<()> {
+        let state = SessionStateBuilder::default().build();
+        let empty_schema = DFSchemaRef::new(DFSchema::empty());
+        let mut producer = DefaultSubstraitProducer::new(&state);
+
+        let expr = lit(1i64) + lit(2i64);
+        let substrait_expr = producer.handle_expr(&expr, &empty_schema)?;
+        if let Expression {
+            rex_type: Some(RexType::ScalarFunction(ScalarFunction { output_type, .. })),
+        } = substrait_expr
+        {
+            let expected_type =
+                to_substrait_type(&mut producer, &DataType::Int64, false)?;
+            assert_eq!(output_type, Some(expected_type));
+            Ok(())
+        } else {
+            panic!("Substrait ScalarFunction expected")
+        }
+    }
+}