feat(substrait): handle emit_kind when consuming Substrait plans

datafusion/substrait/src/logical_plan/consumer.rs

@@ -55,6 +55,7 @@ use crate::variation_const::{
 use datafusion::arrow::array::{new_empty_array, AsArray};
 use datafusion::common::scalar::ScalarStructBuilder;
 use datafusion::dataframe::DataFrame;
+use datafusion::logical_expr::builder::project;
 use datafusion::logical_expr::expr::InList;
 use datafusion::logical_expr::{
     col, expr, Cast, Extension, GroupingSet, Like, LogicalPlanBuilder, Partitioning,
@@ -79,6 +80,7 @@ use substrait::proto::expression::literal::{
 use substrait::proto::expression::subquery::SubqueryType;
 use substrait::proto::expression::{self, FieldReference, Literal, ScalarFunction};
 use substrait::proto::read_rel::local_files::file_or_files::PathType::UriFile;
+use substrait::proto::rel_common::{Emit, EmitKind};
 use substrait::proto::{
     aggregate_function::AggregationInvocation,
     expression::{
@@ -92,9 +94,9 @@ use substrait::proto::{
     join_rel, plan_rel, r#type,
     read_rel::ReadType,
     rel::RelType,
-    set_rel,
+    rel_common, set_rel,
     sort_field::{SortDirection, SortKind::*},
-    AggregateFunction, Expression, NamedStruct, Plan, Rel, Type,
+    AggregateFunction, Expression, NamedStruct, Plan, Rel, RelCommon, Type,
 };
 use substrait::proto::{ExtendedExpression, FunctionArgument, SortField};
 
@@ -560,42 +562,51 @@ pub async fn from_substrait_rel(
     rel: &Rel,
     extensions: &Extensions,
 ) -> Result<LogicalPlan> {
-    match &rel.rel_type {
+    let plan: Result<LogicalPlan> = match &rel.rel_type {
         Some(RelType::Project(p)) => {
             if let Some(input) = p.input.as_ref() {
                 let mut input = LogicalPlanBuilder::from(
                     from_substrait_rel(ctx, input, extensions).await?,
                 );
-                let mut names: HashSet<String> = HashSet::new();
-                let mut exprs: Vec<Expr> = vec![];
-                for e in &p.expressions {
-                    let x =
-                        from_substrait_rex(ctx, e, input.clone().schema(), extensions)
+                let original_schema = input.schema().clone();
+
+                // Ensure that all expressions have a unique display name, so that
+                // validate_unique_names does not fail when constructing the project.
+                let mut name_tracker = NameTracker::new();
+
+                // By default, a Substrait Project emits all inputs fields followed by all expressions.
+                // We build the explicit expressions first, and then the input expressions to avoid
+                // adding aliases to the explicit expressions (as part of ensuring unique names).
+                //
+                // This is helpful for plan visualization and tests, because when DataFusion produces
+                // Substrait Projects it adds an output mapping that excludes all input columns
+                // leaving only explicit expressions.
+
+                let mut explicit_exprs: Vec<Expr> = vec![];
+                for expr in &p.expressions {
+                    let e =
+                        from_substrait_rex(ctx, expr, input.clone().schema(), extensions)
                             .await?;
                     // if the expression is WindowFunction, wrap in a Window relation
-                    if let Expr::WindowFunction(_) = &x {
+                    if let Expr::WindowFunction(_) = &e {
                         // Adding the same expression here and in the project below
                         // works because the project's builder uses columnize_expr(..)
                         // to transform it into a column reference
-                        input = input.window(vec![x.clone()])?
+                        input = input.window(vec![e.clone()])?
                     }
-                    // Ensure the expression has a unique display name, so that project's
-                    // validate_unique_names doesn't fail
-                    let name = x.schema_name().to_string();
-                    let mut new_name = name.clone();
-                    let mut i = 0;
-                    while names.contains(&new_name) {
-                        new_name = format!("{}__temp__{}", name, i);
-                        i += 1;
-                    }
-                    if new_name != name {
-                        exprs.push(x.alias(new_name.clone()));
-                    } else {
-                        exprs.push(x);
-                    }
-                    names.insert(new_name);
+                    explicit_exprs.push(name_tracker.get_uniquely_named_expr(e)?);
                 }
-                input.project(exprs)?.build()
+
+                let mut final_exprs: Vec<Expr> = vec![];
+                for index in 0..original_schema.fields().len() {
+                    let e = Expr::Column(Column::from(
+                        original_schema.qualified_field(index),
+                    ));
+                    final_exprs.push(name_tracker.get_uniquely_named_expr(e)?);
+                }
+                final_exprs.append(&mut explicit_exprs);
+
+                input.project(final_exprs)?.build()
             } else {
                 not_impl_err!("Projection without an input is not supported")
             }
@@ -1059,6 +1070,143 @@ pub async fn from_substrait_rel(
             }))
         }
         _ => not_impl_err!("Unsupported RelType: {:?}", rel.rel_type),
+    };
+    apply_emit_kind(retrieve_rel_common(rel), plan?)
+}
+
+fn retrieve_rel_common(rel: &Rel) -> Option<&RelCommon> {
+    match rel.rel_type.as_ref() {
+        None => None,
+        Some(rt) => match rt {
+            RelType::Read(r) => r.common.as_ref(),
+            RelType::Filter(f) => f.common.as_ref(),
+            RelType::Fetch(f) => f.common.as_ref(),
+            RelType::Aggregate(a) => a.common.as_ref(),
+            RelType::Sort(s) => s.common.as_ref(),
+            RelType::Join(j) => j.common.as_ref(),
+            RelType::Project(p) => p.common.as_ref(),
+            RelType::Set(s) => s.common.as_ref(),
+            RelType::ExtensionSingle(e) => e.common.as_ref(),
+            RelType::ExtensionMulti(e) => e.common.as_ref(),
+            RelType::ExtensionLeaf(e) => e.common.as_ref(),
+            RelType::Cross(c) => c.common.as_ref(),
+            RelType::Reference(_) => None,
+            RelType::Write(w) => w.common.as_ref(),
+            RelType::Ddl(d) => d.common.as_ref(),
+            RelType::HashJoin(j) => j.common.as_ref(),
+            RelType::MergeJoin(j) => j.common.as_ref(),
+            RelType::NestedLoopJoin(j) => j.common.as_ref(),
+            RelType::Window(w) => w.common.as_ref(),
+            RelType::Exchange(e) => e.common.as_ref(),
+            RelType::Expand(e) => e.common.as_ref(),
+        },
+    }
+}
+
+fn retrieve_emit_kind(rel_common: Option<&RelCommon>) -> EmitKind {
+    // the default EmitKind is Direct if it is not set explicitly
+    let default = EmitKind::Direct(rel_common::Direct {});
+    rel_common
+        .and_then(|rc| rc.emit_kind.as_ref())
+        .map_or(default, |ek| ek.clone())
+}
+
+fn contains_volatile_expr(proj: &Projection) -> Result<bool> {
+    for expr in proj.expr.iter() {
+        if expr.is_volatile()? {
+            return Ok(true);
+        }
+    }
+    Ok(false)
+}
+
+fn apply_emit_kind(
+    rel_common: Option<&RelCommon>,
+    plan: LogicalPlan,
+) -> Result<LogicalPlan> {
+    match retrieve_emit_kind(rel_common) {
+        EmitKind::Direct(_) => Ok(plan),
+        EmitKind::Emit(Emit { output_mapping }) => {
+            // It is valid to reference the same field multiple times in the Emit
+            // In this case, we need to provide unique names to avoid collisions
+            let mut name_tracker = NameTracker::new();
+            match plan {
+                // To avoid adding a projection on top of a projection, we apply special case
+                // handling to flatten Substrait Emits. This is only applicable if none of the
+                // expressions in the projection are volatile. This is to avoid issues like
+                // converting a single call of the random() function into multiple calls due to
+                // duplicate fields in the output_mapping.
+                LogicalPlan::Projection(proj) if !contains_volatile_expr(&proj)? => {
+                    let mut exprs: Vec<Expr> = vec![];
+                    for field in output_mapping {
+                        let expr = proj.expr
+                            .get(field as usize)
+                            .ok_or_else(|| substrait_datafusion_err!(
+                                  "Emit output field {} cannot be resolved in input schema {}",
+                                  field, proj.input.schema().clone()
+                                ))?;
+                        exprs.push(name_tracker.get_uniquely_named_expr(expr.clone())?);
+                    }
+
+                    let input = Arc::unwrap_or_clone(proj.input);
+                    project(input, exprs)
+                }
+                // Otherwise we just handle the output_mapping as a projection
+                _ => {
+                    let input_schema = plan.schema();
+
+                    let mut exprs: Vec<Expr> = vec![];
+                    for index in output_mapping.into_iter() {
+                        let column = Expr::Column(Column::from(
+                            input_schema.qualified_field(index as usize),
+                        ));
+                        let expr = name_tracker.get_uniquely_named_expr(column)?;
+                        exprs.push(expr);
+                    }
+
+                    project(plan, exprs)
+                }
+            }
+        }
+    }
+}
+
+struct NameTracker {
+    seen_names: HashSet<String>,
+}
+
+enum NameTrackerStatus {
+    NeverSeen,
+    SeenBefore,
+}
+
+impl NameTracker {
+    fn new() -> Self {
+        NameTracker {
+            seen_names: HashSet::default(),
+        }
+    }
+    fn get_unique_name(&mut self, name: String) -> (String, NameTrackerStatus) {
+        match self.seen_names.insert(name.clone()) {
+            true => (name, NameTrackerStatus::NeverSeen),
+            false => {
+                let mut counter = 0;
+                loop {
+                    let candidate_name = format!("{}__temp__{}", name, counter);
+                    if self.seen_names.insert(candidate_name.clone()) {
+                        return (candidate_name, NameTrackerStatus::SeenBefore);
+                    }
+                    counter += 1;
+                }
+            }
+        }
+    }
+
+    fn get_uniquely_named_expr(&mut self, expr: Expr) -> Result<Expr> {
+        match self.get_unique_name(expr.name_for_alias()?) {
+            (_, NameTrackerStatus::NeverSeen) => Ok(expr),
+            (name, NameTrackerStatus::SeenBefore) => Ok(expr.alias(name)),
+        }
     }
 }
 

datafusion/substrait/tests/cases/emit_kind_tests.rs

@@ -0,0 +1,127 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Tests for Emit Kind usage
+
+#[cfg(test)]
+mod tests {
+    use crate::utils::test::{add_plan_schemas_to_ctx, read_json};
+
+    use datafusion::common::Result;
+    use datafusion::execution::SessionStateBuilder;
+    use datafusion::prelude::{CsvReadOptions, SessionConfig, SessionContext};
+    use datafusion_substrait::logical_plan::consumer::from_substrait_plan;
+    use datafusion_substrait::logical_plan::producer::to_substrait_plan;
+
+    #[tokio::test]
+    async fn project_respects_direct_emit_kind() -> Result<()> {
+        let proto_plan = read_json(
+            "tests/testdata/test_plans/emit_kind/direct_on_project.substrait.json",
+        );
+        let ctx = add_plan_schemas_to_ctx(SessionContext::new(), &proto_plan)?;
+        let plan = from_substrait_plan(&ctx, &proto_plan).await?;
+
+        let plan_str = format!("{}", plan);
+
+        assert_eq!(
+            plan_str,
+            "Projection: DATA.A AS a, DATA.B AS b, DATA.A + Int64(1) AS add1\
+            \n  TableScan: DATA"
+        );
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn handle_emit_as_project() -> Result<()> {
+        let proto_plan = read_json(
+            "tests/testdata/test_plans/emit_kind/emit_on_filter.substrait.json",
+        );
+        let ctx = add_plan_schemas_to_ctx(SessionContext::new(), &proto_plan)?;
+        let plan = from_substrait_plan(&ctx, &proto_plan).await?;
+
+        let plan_str = format!("{}", plan);
+
+        assert_eq!(
+            plan_str,
+            // Note that duplicate references in the remap are aliased
+            "Projection: DATA.B, DATA.A AS A1, DATA.A AS DATA.A__temp__0 AS A2\
+             \n  Filter: DATA.B = Int64(2)\
+             \n    TableScan: DATA"
+        );
+        Ok(())
+    }
+
+    async fn make_context() -> Result<SessionContext> {
+        let state = SessionStateBuilder::new()
+            .with_config(SessionConfig::default())
+            .with_default_features()
+            .build();
+        let ctx = SessionContext::new_with_state(state);
+        ctx.register_csv("data", "tests/testdata/data.csv", CsvReadOptions::default())
+            .await?;
+        Ok(ctx)
+    }
+
+    #[tokio::test]
+    async fn handle_emit_as_project_with_volatile_expr() -> Result<()> {
+        let ctx = make_context().await?;
+
+        let df = ctx
+            .sql("SELECT random() AS c1, a + 1 AS c2 FROM data")
+            .await?;
+
+        let plan = df.into_unoptimized_plan();
+        assert_eq!(
+            format!("{}", plan),
+            "Projection: random() AS c1, data.a + Int64(1) AS c2\
+             \n  TableScan: data"
+        );
+
+        let proto = to_substrait_plan(&plan, &ctx)?;
+        let plan2 = from_substrait_plan(&ctx, &proto).await?;
+        // note how the Projections are not flattened
+        assert_eq!(
+            format!("{}", plan2),
+            "Projection: random() AS c1, data.a + Int64(1) AS c2\
+             \n  Projection: data.a, data.b, data.c, data.d, data.e, data.f, random(), data.a + Int64(1)\
+             \n    TableScan: data"
+        );
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn handle_emit_as_project_without_volatile_exprs() -> Result<()> {
+        let ctx = make_context().await?;
+        let df = ctx.sql("SELECT a + 1, b + 2 FROM data").await?;
+
+        let plan = df.into_unoptimized_plan();
+        assert_eq!(
+            format!("{}", plan),
+            "Projection: data.a + Int64(1), data.b + Int64(2)\
+             \n  TableScan: data"
+        );
+
+        let proto = to_substrait_plan(&plan, &ctx)?;
+        let plan2 = from_substrait_plan(&ctx, &proto).await?;
+
+        let plan1str = format!("{plan}");
+        let plan2str = format!("{plan2}");
+        assert_eq!(plan1str, plan2str);
+
+        Ok(())
+    }
+}

datafusion/substrait/tests/cases/mod.rs

@@ -16,6 +16,7 @@
 // under the License.
 
 mod consumer_integration;
+mod emit_kind_tests;
 mod function_test;
 mod logical_plans;
 mod roundtrip_logical_plan;