Add can_pushdown_predicate fn to evaluate ast expressions for constness

core/util.rs

@@ -2,6 +2,7 @@ use limbo_sqlite3_parser::ast::{self, CreateTableBody, Expr, FunctionTail, Liter
 use std::{rc::Rc, sync::Arc};
 
 use crate::{
+    function::Func,
     schema::{self, Column, Schema, Type},
     types::{OwnedValue, OwnedValueType},
     LimboError, OpenFlags, Result, Statement, StepResult, SymbolTable, IO,
@@ -565,6 +566,41 @@ pub fn columns_from_create_table_body(body: &ast::CreateTableBody) -> crate::Res
         .collect::<Vec<_>>())
 }
 
+pub fn can_pushdown_predicate(expr: &Expr) -> bool {
+    match expr {
+        Expr::Literal(_) => true,
+        Expr::Column { .. } => true,
+        Expr::Binary(lhs, _, rhs) => can_pushdown_predicate(lhs) && can_pushdown_predicate(rhs),
+        Expr::Parenthesized(exprs) => can_pushdown_predicate(exprs.first().unwrap()),
+        Expr::Unary(_, expr) => can_pushdown_predicate(expr),
+        Expr::FunctionCall { args, name, .. } => {
+            let function = crate::function::Func::resolve_function(
+                &name.0,
+                args.as_ref().map_or(0, |a| a.len()),
+            );
+            matches!(function, Ok(Func::Scalar(_)))
+        }
+        Expr::Like { lhs, rhs, .. } => can_pushdown_predicate(lhs) && can_pushdown_predicate(rhs),
+        Expr::Between {
+            lhs, start, end, ..
+        } => {
+            can_pushdown_predicate(lhs)
+                && can_pushdown_predicate(start)
+                && can_pushdown_predicate(end)
+        }
+        Expr::Id(_) => true,
+        Expr::Name(_) => true,
+        Expr::Qualified(_, _) => true,
+        Expr::DoublyQualified(_, _, _) => true,
+        Expr::InTable { lhs, .. } => can_pushdown_predicate(lhs),
+        _ => false,
+    }
+}
+
+fn is_deterministic(func: &Func) -> bool {
+    matches!(func, Func::Scalar(_))
+}
+
 #[derive(Debug, Default, PartialEq)]
 pub struct OpenOptions<'a> {
     /// The authority component of the URI. may be 'localhost' or empty