feat[vortex-expr]: is_fallible expression analysis (#5531)

For now we put this on the VTable, but I think we should figure out a
way to make this analysis extensible

---------

Signed-off-by: Joe Isaacs <[email protected]>

Author: joseph-isaacs

vortex-array/src/expr/analysis/labeling.rs

@@ -62,6 +62,10 @@ where
 {
     type NodeTy = Expression;
 
+    fn visit_down(&mut self, _node: &'a Self::NodeTy) -> VortexResult<TraversalOrder> {
+        Ok(TraversalOrder::Continue)
+    }
+
     fn visit_up(&mut self, node: &'a Expression) -> VortexResult<TraversalOrder> {
         let self_label = (self.self_label)(node);
 

vortex-array/src/expr/expression.rs

@@ -238,6 +238,12 @@ impl Expression {
         self.vtable.as_dyn().is_null_sensitive(self.data.as_ref())
     }
 
+    /// Returns whether this expression itself is fallible.
+    /// See [`VTable::is_fallible`].
+    pub fn is_fallible(&self) -> bool {
+        self.vtable.as_dyn().is_fallible(self.data.as_ref())
+    }
+
     /// Format the expression as a compact string.
     ///
     /// Since this is a recursive formatter, it is exposed on the public Expression type.

vortex-array/src/expr/exprs/get_item/mod.rs

@@ -155,6 +155,11 @@ impl VTable for GetItem {
     fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
         true
     }
+
+    fn is_fallible(&self, _instance: &Self::Instance) -> bool {
+        // If this type-checks its infallible.
+        false
+    }
 }
 
 /// Creates an expression that accesses a field from the root array.

vortex-array/src/expr/exprs/is_null.rs

@@ -106,6 +106,10 @@ impl VTable for IsNull {
     fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
         true
     }
+
+    fn is_fallible(&self, _instance: &Self::Instance) -> bool {
+        false
+    }
 }
 
 /// Creates an expression that checks for null values.

vortex-array/src/expr/exprs/literal.rs

@@ -130,6 +130,10 @@ impl VTable for Literal {
     fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
         false
     }
+
+    fn is_fallible(&self, _instance: &Self::Instance) -> bool {
+        false
+    }
 }
 
 /// Create a new `Literal` expression from a type that coerces to `Scalar`.

vortex-array/src/expr/exprs/merge/mod.rs

@@ -166,6 +166,14 @@ impl VTable for Merge {
                 .into_array(),
         )
     }
+
+    fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
+        true
+    }
+
+    fn is_fallible(&self, instance: &Self::Instance) -> bool {
+        matches!(instance, DuplicateHandling::Error)
+    }
 }
 
 /// What to do when merged structs share a field name.

vortex-array/src/expr/exprs/not.rs

@@ -85,6 +85,10 @@ impl VTable for Not {
     fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
         false
     }
+
+    fn is_fallible(&self, _instance: &Self::Instance) -> bool {
+        false
+    }
 }
 
 /// Creates an expression that logically inverts boolean values.

vortex-array/src/expr/exprs/pack.rs

@@ -145,6 +145,10 @@ impl VTable for Pack {
     fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
         true
     }
+
+    fn is_fallible(&self, _instance: &Self::Instance) -> bool {
+        false
+    }
 }
 
 impl ExpressionView<'_, Pack> {

vortex-array/src/expr/exprs/root.rs

@@ -85,6 +85,10 @@ impl VTable for Root {
     fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
         false
     }
+
+    fn is_fallible(&self, _instance: &Self::Instance) -> bool {
+        false
+    }
 }
 
 /// Creates an expression that references the root scope.

vortex-array/src/expr/exprs/select/mod.rs

@@ -201,6 +201,15 @@ impl VTable for Select {
             .collect();
         Ok(unsafe { StructVector::new_unchecked(Arc::new(new_fields), mask) }.into())
     }
+
+    fn is_null_sensitive(&self, _instance: &Self::Instance) -> bool {
+        true
+    }
+
+    fn is_fallible(&self, _instance: &Self::Instance) -> bool {
+        // If this type-checks its infallible.
+        false
+    }
 }
 
 /// Creates an expression that selects (includes) specific fields from an array.