refactor: Add a TypeCheckRule to the optimizer

crates/polars-lazy/src/frame/mod.rs

@@ -172,6 +172,12 @@ impl LazyFrame {
         self
     }
 
+    /// Toggle type check optimization.
+    pub fn with_type_check(mut self, toggle: bool) -> Self {
+        self.opt_state.set(OptFlags::TYPE_CHECK, toggle);
+        self
+    }
+
     /// Toggle expression simplification optimization on or off.
     pub fn with_simplify_expr(mut self, toggle: bool) -> Self {
         self.opt_state.set(OptFlags::SIMPLIFY_EXPR, toggle);

crates/polars-plan/src/dsl/expr_dyn_fn.rs

@@ -295,6 +295,12 @@ impl GetOutput {
         Default::default()
     }
 
+    pub fn first() -> Self {
+        SpecialEq::new(Arc::new(
+            |_input_schema: &Schema, _cntxt: Context, fields: &[Field]| Ok(fields[0].clone()),
+        ))
+    }
+
     pub fn from_type(dt: DataType) -> Self {
         SpecialEq::new(Arc::new(move |_: &Schema, _: Context, flds: &[Field]| {
             Ok(Field::new(flds[0].name().clone(), dt.clone()))

crates/polars-plan/src/dsl/functions/horizontal.rs

@@ -25,15 +25,15 @@ where
     F: 'static + Fn(Column, Column) -> PolarsResult<Option<Column>> + Send + Sync,
     E: AsRef<[Expr]>,
 {
-    let mut exprs = exprs.as_ref().to_vec();
-    exprs.push(acc);
+    let mut exprs_v = Vec::with_capacity(exprs.as_ref().len() + 1);
+    exprs_v.push(acc);
+    exprs_v.extend(exprs.as_ref().iter().cloned());
+    let exprs = exprs_v;
 
     let function = new_column_udf(move |columns: &mut [Column]| {
-        let mut columns = columns.to_vec();
-        let mut acc = columns.pop().unwrap();
-
-        for c in columns {
-            if let Some(a) = f(acc.clone(), c)? {
+        let mut acc = columns.first().unwrap().clone();
+        for c in &columns[1..] {
+            if let Some(a) = f(acc.clone(), c.clone())? {
                 acc = a
             }
         }
@@ -43,7 +43,8 @@ where
     Expr::AnonymousFunction {
         input: exprs,
         function,
-        output_type: GetOutput::super_type(),
+        // Take the type of the accumulator.
+        output_type: GetOutput::first(),
         options: FunctionOptions {
             collect_groups: ApplyOptions::GroupWise,
             flags: FunctionFlags::default()

crates/polars-plan/src/frame/opt_state.rs

@@ -38,12 +38,14 @@ bitflags! {
         /// Check if operations are order dependent and unset maintaining_order if
         /// the order would not be observed.
         const CHECK_ORDER_OBSERVE = 1 << 16;
+        /// Do type checking of the IR.
+        const TYPE_CHECK = 1 << 17;
     }
 }
 
 impl OptFlags {
     pub fn schema_only() -> Self {
-        Self::TYPE_COERCION
+        Self::TYPE_COERCION | Self::TYPE_CHECK
     }
 }
 

crates/polars-plan/src/plans/conversion/dsl_to_ir.rs

@@ -63,12 +63,13 @@ pub fn to_alp(
     lp: DslPlan,
     expr_arena: &mut Arena<AExpr>,
     lp_arena: &mut Arena<IR>,
-    // Only `SIMPLIFY_EXPR` and `TYPE_COERCION` are respected.
+    // Only `SIMPLIFY_EXPR`, `TYPE_COERCION`, `TYPE_CHECK` are respected.
     opt_flags: &mut OptFlags,
 ) -> PolarsResult<Node> {
     let conversion_optimizer = ConversionOptimizer::new(
         opt_flags.contains(OptFlags::SIMPLIFY_EXPR),
         opt_flags.contains(OptFlags::TYPE_COERCION),
+        opt_flags.contains(OptFlags::TYPE_CHECK),
     );
 
     let mut ctxt = DslConversionContext {

crates/polars-plan/src/plans/conversion/join.rs

@@ -120,6 +120,9 @@ pub fn resolve_join(
         .coerce_types(ctxt.expr_arena, ctxt.lp_arena, input_right)
         .map_err(|e| e.context("'join' failed".into()))?;
 
+    let schema_left = ctxt.lp_arena.get(input_left).schema(ctxt.lp_arena);
+    let schema_right = ctxt.lp_arena.get(input_right).schema(ctxt.lp_arena);
+
     // Not a closure to avoid borrow issues because we mutate expr_arena as well.
     macro_rules! get_dtype {
         ($expr:expr, $schema:expr) => {

crates/polars-plan/src/plans/conversion/mod.rs

@@ -12,16 +12,20 @@ mod ir_to_dsl;
 mod scans;
 mod stack_opt;
 
+use std::borrow::Cow;
 use std::sync::{Arc, Mutex};
 
 pub use dsl_to_ir::*;
 pub use expr_to_ir::*;
 pub use ir_to_dsl::*;
 use polars_core::prelude::*;
+use polars_utils::idx_vec::UnitVec;
+use polars_utils::unitvec;
 use polars_utils::vec::ConvertVec;
 use recursive::recursive;
 mod functions;
 mod join;
+pub(crate) mod type_check;
 pub(crate) mod type_coercion;
 
 pub(crate) use expr_expansion::{expand_selectors, is_regex_projection, prepare_projection};
@@ -266,3 +270,27 @@ impl IR {
         }
     }
 }
+
+fn get_input(lp_arena: &Arena<IR>, lp_node: Node) -> UnitVec<Node> {
+    let plan = lp_arena.get(lp_node);
+    let mut inputs: UnitVec<Node> = unitvec!();
+
+    // Used to get the schema of the input.
+    if is_scan(plan) {
+        inputs.push(lp_node);
+    } else {
+        plan.copy_inputs(&mut inputs);
+    };
+    inputs
+}
+
+fn get_schema(lp_arena: &Arena<IR>, lp_node: Node) -> Cow<'_, SchemaRef> {
+    let inputs = get_input(lp_arena, lp_node);
+    if inputs.is_empty() {
+        // Files don't have an input, so we must take their schema.
+        Cow::Borrowed(lp_arena.get(lp_node).scan_schema())
+    } else {
+        let input = inputs[0];
+        lp_arena.get(input).schema(lp_arena)
+    }
+}

crates/polars-plan/src/plans/conversion/stack_opt.rs

@@ -1,12 +1,15 @@
 use std::borrow::Borrow;
 
+use self::type_check::TypeCheckRule;
 use super::*;
 
 /// Applies expression simplification and type coercion during conversion to IR.
 pub(super) struct ConversionOptimizer {
     scratch: Vec<Node>,
+
     simplify: Option<SimplifyExprRule>,
     coerce: Option<TypeCoercionRule>,
+    check: Option<TypeCheckRule>,
     // IR's can be cached in the DSL.
     // But if they are used multiple times in DSL (e.g. concat/join)
     // then it can occur that we take a slot multiple times.
@@ -16,7 +19,7 @@ pub(super) struct ConversionOptimizer {
 }
 
 impl ConversionOptimizer {
-    pub(super) fn new(simplify: bool, type_coercion: bool) -> Self {
+    pub(super) fn new(simplify: bool, type_coercion: bool, type_check: bool) -> Self {
         let simplify = if simplify {
             Some(SimplifyExprRule {})
         } else {
@@ -29,10 +32,17 @@ impl ConversionOptimizer {
             None
         };
 
+        let check = if type_check {
+            Some(TypeCheckRule)
+        } else {
+            None
+        };
+
         ConversionOptimizer {
             scratch: Vec::with_capacity(8),
             simplify,
             coerce,
+            check,
             used_arenas: Default::default(),
         }
     }
@@ -54,29 +64,35 @@ impl ConversionOptimizer {
     pub(super) fn coerce_types(
         &mut self,
         expr_arena: &mut Arena<AExpr>,
-        lp_arena: &Arena<IR>,
+        ir_arena: &mut Arena<IR>,
         current_node: Node,
     ) -> PolarsResult<()> {
         // Different from the stack-opt in the optimizer phase, this does a single pass until fixed point per expression.
 
+        if let Some(rule) = &mut self.check {
+            while let Some(x) = rule.optimize_plan(ir_arena, expr_arena, current_node)? {
+                ir_arena.replace(current_node, x);
+            }
+        }
+
         // process the expressions on the stack and apply optimizations.
         while let Some(current_expr_node) = self.scratch.pop() {
-            {
-                let expr = unsafe { expr_arena.get_unchecked(current_expr_node) };
-                if expr.is_leaf() {
-                    continue;
-                }
+            let expr = unsafe { expr_arena.get_unchecked(current_expr_node) };
+
+            if expr.is_leaf() {
+                continue;
             }
+
             if let Some(rule) = &mut self.simplify {
                 while let Some(x) =
-                    rule.optimize_expr(expr_arena, current_expr_node, lp_arena, current_node)?
+                    rule.optimize_expr(expr_arena, current_expr_node, ir_arena, current_node)?
                 {
                     expr_arena.replace(current_expr_node, x);
                 }
             }
             if let Some(rule) = &mut self.coerce {
                 while let Some(x) =
-                    rule.optimize_expr(expr_arena, current_expr_node, lp_arena, current_node)?
+                    rule.optimize_expr(expr_arena, current_expr_node, ir_arena, current_node)?
                 {
                     expr_arena.replace(current_expr_node, x);
                 }

crates/polars-plan/src/plans/conversion/type_check/mod.rs

@@ -0,0 +1,48 @@
+use polars_core::error::{polars_ensure, PolarsResult};
+use polars_core::prelude::DataType;
+use polars_utils::arena::{Arena, Node};
+
+use super::{AExpr, OptimizationRule, IR};
+use crate::plans::conversion::get_schema;
+use crate::plans::Context;
+
+pub struct TypeCheckRule;
+
+impl OptimizationRule for TypeCheckRule {
+    fn optimize_plan(
+        &mut self,
+        ir_arena: &mut Arena<IR>,
+        expr_arena: &mut Arena<AExpr>,
+        node: Node,
+    ) -> PolarsResult<Option<IR>> {
+        let ir = ir_arena.get(node);
+        match ir {
+            IR::Scan {
+                predicate: Some(predicate),
+                ..
+            } => {
+                let input_schema = get_schema(ir_arena, node);
+                let dtype = predicate.dtype(input_schema.as_ref(), Context::Default, expr_arena)?;
+
+                polars_ensure!(
+                    matches!(dtype, DataType::Boolean | DataType::Unknown(_)),
+                    InvalidOperation: "filter predicate must be of type `Boolean`, got `{dtype:?}`"
+                );
+
+                Ok(None)
+            },
+            IR::Filter { predicate, .. } => {
+                let input_schema = get_schema(ir_arena, node);
+                let dtype = predicate.dtype(input_schema.as_ref(), Context::Default, expr_arena)?;
+
+                polars_ensure!(
+                    matches!(dtype, DataType::Boolean | DataType::Unknown(_)),
+                    InvalidOperation: "filter predicate must be of type `Boolean`, got `{dtype:?}`"
+                );
+
+                Ok(None)
+            },
+            _ => Ok(None),
+        }
+    }
+}

crates/polars-plan/src/plans/conversion/type_coercion/mod.rs

@@ -3,16 +3,13 @@ mod functions;
 #[cfg(feature = "is_in")]
 mod is_in;
 
-use std::borrow::Cow;
-
 use binary::process_binary;
 use polars_compute::cast::temporal::{time_unit_multiple, SECONDS_IN_DAY};
 use polars_core::chunked_array::cast::CastOptions;
 use polars_core::prelude::*;
 use polars_core::utils::{get_supertype, get_supertype_with_options, materialize_dyn_int};
-use polars_utils::idx_vec::UnitVec;
+use polars_utils::format_list;
 use polars_utils::itertools::Itertools;
-use polars_utils::{format_list, unitvec};
 
 use super::*;
 
@@ -69,30 +66,6 @@ fn modify_supertype(
     st
 }
 
-fn get_input(lp_arena: &Arena<IR>, lp_node: Node) -> UnitVec<Node> {
-    let plan = lp_arena.get(lp_node);
-    let mut inputs: UnitVec<Node> = unitvec!();
-
-    // Used to get the schema of the input.
-    if is_scan(plan) {
-        inputs.push(lp_node);
-    } else {
-        plan.copy_inputs(&mut inputs);
-    };
-    inputs
-}
-
-fn get_schema(lp_arena: &Arena<IR>, lp_node: Node) -> Cow<'_, SchemaRef> {
-    let inputs = get_input(lp_arena, lp_node);
-    if inputs.is_empty() {
-        // Files don't have an input, so we must take their schema.
-        Cow::Borrowed(lp_arena.get(lp_node).scan_schema())
-    } else {
-        let input = inputs[0];
-        lp_arena.get(input).schema(lp_arena)
-    }
-}
-
 fn get_aexpr_and_type<'a>(
     expr_arena: &'a Arena<AExpr>,
     e: Node,
@@ -515,6 +488,7 @@ fn cast_expr_ir(
     if let AExpr::Literal(lv) = expr_arena.get(e.node()) {
         if let Some(literal) = try_inline_literal_cast(lv, to_dtype, strict)? {
             e.set_node(expr_arena.add(AExpr::Literal(literal)));
+            e.set_dtype(to_dtype.clone());
             return Ok(());
         }
     }
@@ -524,6 +498,8 @@ fn cast_expr_ir(
         dtype: to_dtype.clone(),
         options: CastOptions::Strict,
     }));
+    e.set_dtype(to_dtype.clone());
+
     Ok(())
 }
 

crates/polars-plan/src/plans/expr_ir.rs

@@ -106,6 +106,10 @@ impl ExprIR {
         self
     }
 
+    pub(crate) fn set_dtype(&mut self, dtype: DataType) {
+        self.output_dtype = OnceLock::from(dtype);
+    }
+
     pub fn from_node(node: Node, arena: &Arena<AExpr>) -> Self {
         let mut out = Self {
             node,