alamb commented on code in PR #3796:
URL: https://github.com/apache/arrow-datafusion/pull/3796#discussion_r993468214


##########
datafusion/expr/src/logical_plan/plan.rs:
##########
@@ -1148,18 +1150,72 @@ pub struct SubqueryAlias {
 #[derive(Clone)]
 pub struct Filter {
     /// The predicate expression, which must have Boolean type.
-    pub predicate: Expr,
+    predicate: Expr,
     /// The incoming logical plan
-    pub input: Arc<LogicalPlan>,
+    input: Arc<LogicalPlan>,
 }
 
 impl Filter {
+    /// Create a new filter operator.
+    pub fn try_new(
+        predicate: Expr,
+        input: Arc<LogicalPlan>,
+    ) -> datafusion_common::Result<Self> {
+        // Filter predicates must return a boolean value so we try and 
validate that here.
+        // Note that it is not always possible to resolve the predicate 
expression during plan
+        // construction (such as with correlated subqueries) so we make a best 
effort here and
+        // ignore errors resolving the expression against the schema.
+        if let Ok(predicate_type) = predicate.get_type(input.schema()) {
+            if predicate_type != DataType::Boolean {
+                return Err(DataFusionError::Plan(format!(
+                    "Cannot create filter with non-boolean predicate '{}' 
returning {}",
+                    predicate, predicate_type
+                )));
+            }
+        }
+
+        // filter predicates should not contain aliased expressions so we 
remove any aliases here
+        // but perhaps we should be failing here instead?
+        struct RemoveAliases {}
+
+        impl ExprRewriter for RemoveAliases {
+            fn mutate(&mut self, expr: Expr) -> 
datafusion_common::Result<Expr> {
+                match expr {
+                    Expr::Alias(expr, alias) => {
+                        debug!(
+                            "Attempted to create Filter predicate containing 
aliased \
+                            expression `{}` AS '{}'",
+                            expr, alias
+                        );
+                        Ok(expr.as_ref().clone())

Review Comment:
   ```suggestion
                           Ok(expr)
   ```



##########
datafusion/expr/src/logical_plan/plan.rs:
##########
@@ -1148,18 +1150,72 @@ pub struct SubqueryAlias {
 #[derive(Clone)]
 pub struct Filter {
     /// The predicate expression, which must have Boolean type.
-    pub predicate: Expr,
+    predicate: Expr,
     /// The incoming logical plan
-    pub input: Arc<LogicalPlan>,
+    input: Arc<LogicalPlan>,
 }
 
 impl Filter {
+    /// Create a new filter operator.
+    pub fn try_new(
+        predicate: Expr,
+        input: Arc<LogicalPlan>,
+    ) -> datafusion_common::Result<Self> {
+        // Filter predicates must return a boolean value so we try and 
validate that here.
+        // Note that it is not always possible to resolve the predicate 
expression during plan
+        // construction (such as with correlated subqueries) so we make a best 
effort here and
+        // ignore errors resolving the expression against the schema.
+        if let Ok(predicate_type) = predicate.get_type(input.schema()) {
+            if predicate_type != DataType::Boolean {
+                return Err(DataFusionError::Plan(format!(
+                    "Cannot create filter with non-boolean predicate '{}' 
returning {}",
+                    predicate, predicate_type
+                )));
+            }
+        }
+
+        // filter predicates should not contain aliased expressions so we 
remove any aliases here
+        // but perhaps we should be failing here instead?
+        struct RemoveAliases {}
+
+        impl ExprRewriter for RemoveAliases {
+            fn mutate(&mut self, expr: Expr) -> 
datafusion_common::Result<Expr> {
+                match expr {
+                    Expr::Alias(expr, alias) => {
+                        debug!(
+                            "Attempted to create Filter predicate containing 
aliased \
+                            expression `{}` AS '{}'",
+                            expr, alias
+                        );
+                        Ok(expr.as_ref().clone())
+                    }
+                    _ => Ok(expr.clone()),

Review Comment:
   ```suggestion
                       _ => Ok(expr),
   ```



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