[SPARK-28228][SQL] Change the default behavior for name conflict in nested WITH clause

docs/sql-migration-guide.md

@@ -103,7 +103,7 @@ license: |
 
   - Since Spark 3.0, if files or subdirectories disappear during recursive directory listing (i.e. they appear in an intermediate listing but then cannot be read or listed during later phases of the recursive directory listing, due to either concurrent file deletions or object store consistency issues) then the listing will fail with an exception unless `spark.sql.files.ignoreMissingFiles` is `true` (default `false`). In previous versions, these missing files or subdirectories would be ignored. Note that this change of behavior only applies during initial table file listing (or during `REFRESH TABLE`), not during query execution: the net change is that `spark.sql.files.ignoreMissingFiles` is now obeyed during table file listing / query planning, not only at query execution time.
 
-  - Since Spark 3.0, substitution order of nested WITH clauses is changed and an inner CTE definition takes precedence over an outer. In version 2.4 and earlier, `WITH t AS (SELECT 1), t2 AS (WITH t AS (SELECT 2) SELECT * FROM t) SELECT * FROM t2` returns `1` while in version 3.0 it returns `2`. The previous behaviour can be restored by setting `spark.sql.legacy.ctePrecedence.enabled` to `true`.
+  - Since Spark 3.0, Spark throws an AnalysisException if name conflict is detected in the nested WITH clause. It forces the users to choose the specific substitution order they wanted, which is controlled by `spark.sql.legacy.ctePrecedence.enabled`. If set to false, inner CTE definitions take precedence over outer definitions. For example, set the config to `false`, `WITH t AS (SELECT 1), t2 AS (WITH t AS (SELECT 2) SELECT * FROM t) SELECT * FROM t2` returns `2`, while setting it to `true`, the result is `1` which is the behavior in version 2.4 and earlier.
 
   - Since Spark 3.0, the `add_months` function does not adjust the resulting date to a last day of month if the original date is a last day of months. For example, `select add_months(DATE'2019-02-28', 1)` results `2019-03-28`. In Spark version 2.4 and earlier, the resulting date is adjusted when the original date is a last day of months. For example, adding a month to `2019-02-28` results in `2019-03-31`.
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CTESubstitution.scala

@@ -17,6 +17,7 @@
 
 package org.apache.spark.sql.catalyst.analysis
 
+import org.apache.spark.sql.AnalysisException
 import org.apache.spark.sql.catalyst.expressions.SubqueryExpression
 import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, With}
 import org.apache.spark.sql.catalyst.rules.Rule
@@ -28,13 +29,55 @@ import org.apache.spark.sql.internal.SQLConf.LEGACY_CTE_PRECEDENCE_ENABLED
  */
 object CTESubstitution extends Rule[LogicalPlan] {
   def apply(plan: LogicalPlan): LogicalPlan = {
-    if (SQLConf.get.getConf(LEGACY_CTE_PRECEDENCE_ENABLED)) {
+    val isLegacy = SQLConf.get.getConf(LEGACY_CTE_PRECEDENCE_ENABLED)
+    if (isLegacy.isEmpty) {
+      if (detectConflictInNestedCTE(plan, inTraverse = false)) {
+        throw new AnalysisException("Name collision in nested CTE was founded in current plan, " +
+          s"please select the CTE precedence via ${LEGACY_CTE_PRECEDENCE_ENABLED.key}, " +
+          "see more detail in SPARK-28228.")
+      } else {
+        traverseAndSubstituteCTE(plan, inTraverse = false)
+      }
+    } else if (isLegacy.get) {
       legacyTraverseAndSubstituteCTE(plan)
     } else {
-      traverseAndSubstituteCTE(plan, false)
+      traverseAndSubstituteCTE(plan, inTraverse = false)
     }
   }
 
+  /**
+   * Check the plan to be traversed has naming conflicts in nested CTE or not, traverse through
+   * child, innerChildren and subquery for the current plan.
+   */
+  private def detectConflictInNestedCTE(
+      plan: LogicalPlan,
+      inTraverse: Boolean,
+      cteNames: Set[String] = Set.empty): Boolean = {
+    plan.foreach {
+      case w @ With(child, relations) =>
+        val newNames = relations.map {
+          case (cteName, _) =>
+            if (cteNames.contains(cteName)) {
+              return true
+            } else {
+              cteName
+            }
+        }.toSet
+        (w.innerChildren :+ child).foreach { p =>
+          if (detectConflictInNestedCTE(p, inTraverse = true, cteNames ++ newNames)) return true
+        }
+
+      case other if inTraverse =>
+        other.transformExpressions {
+          case e: SubqueryExpression
+            if detectConflictInNestedCTE(e.plan, inTraverse = true, cteNames) => return true
+        }
+
+      case _ =>
+    }
+    false
+  }
+
   private def legacyTraverseAndSubstituteCTE(plan: LogicalPlan): LogicalPlan = {
     plan.resolveOperatorsUp {
       case With(child, relations) =>

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -2079,7 +2079,7 @@ object SQLConf {
     .internal()
     .doc("When true, outer CTE definitions takes precedence over inner definitions.")
     .booleanConf
-    .createWithDefault(false)
+    .createOptional
 
   val LEGACY_ARRAY_EXISTS_FOLLOWS_THREE_VALUED_LOGIC =
     buildConf("spark.sql.legacy.arrayExistsFollowsThreeValuedLogic")

sql/core/src/test/resources/sql-tests/inputs/cte-nonlegacy.sql

@@ -0,0 +1,115 @@
+create temporary view t as select * from values 0, 1, 2 as t(id);
+create temporary view t2 as select * from values 0, 1 as t(id);
+
+-- CTE non-legacy substitution
+SET spark.sql.legacy.ctePrecedence.enabled=false;
+
+-- CTE in CTE definition
+WITH t as (
+  WITH t2 AS (SELECT 1)
+  SELECT * FROM t2
+)
+SELECT * FROM t;
+
+-- CTE in subquery
+SELECT max(c) FROM (
+  WITH t(c) AS (SELECT 1)
+  SELECT * FROM t
+);
+
+-- CTE in subquery expression
+SELECT (
+  WITH t AS (SELECT 1)
+  SELECT * FROM t
+);
+
+-- CTE in CTE definition shadows outer
+WITH
+  t AS (SELECT 1),
+  t2 AS (
+    WITH t AS (SELECT 2)
+    SELECT * FROM t
+  )
+SELECT * FROM t2;
+
+-- CTE in CTE definition shadows outer 2
+WITH
+  t(c) AS (SELECT 1),
+  t2 AS (
+    SELECT (
+      SELECT max(c) FROM (
+        WITH t(c) AS (SELECT 2)
+        SELECT * FROM t
+      )
+    )
+  )
+SELECT * FROM t2;
+
+-- CTE in CTE definition shadows outer 3
+WITH
+  t AS (SELECT 1),
+  t2 AS (
+    WITH t AS (SELECT 2),
+    t2 AS (
+      WITH t AS (SELECT 3)
+      SELECT * FROM t
+    )
+    SELECT * FROM t2
+  )
+SELECT * FROM t2;
+
+-- CTE in subquery shadows outer
+WITH t(c) AS (SELECT 1)
+SELECT max(c) FROM (
+  WITH t(c) AS (SELECT 2)
+  SELECT * FROM t
+);
+
+-- CTE in subquery shadows outer 2
+WITH t(c) AS (SELECT 1)
+SELECT sum(c) FROM (
+  SELECT max(c) AS c FROM (
+    WITH t(c) AS (SELECT 2)
+    SELECT * FROM t
+  )
+);
+
+-- CTE in subquery shadows outer 3
+WITH t(c) AS (SELECT 1)
+SELECT sum(c) FROM (
+  WITH t(c) AS (SELECT 2)
+  SELECT max(c) AS c FROM (
+    WITH t(c) AS (SELECT 3)
+    SELECT * FROM t
+  )
+);
+
+-- CTE in subquery expression shadows outer
+WITH t AS (SELECT 1)
+SELECT (
+  WITH t AS (SELECT 2)
+  SELECT * FROM t
+);
+
+-- CTE in subquery expression shadows outer 2
+WITH t AS (SELECT 1)
+SELECT (
+  SELECT (
+    WITH t AS (SELECT 2)
+    SELECT * FROM t
+  )
+);
+
+-- CTE in subquery expression shadows outer 3
+WITH t AS (SELECT 1)
+SELECT (
+  WITH t AS (SELECT 2)
+  SELECT (
+    WITH t AS (SELECT 3)
+    SELECT * FROM t
+  )
+);
+
+-- Clean up
+DROP VIEW IF EXISTS t;
+DROP VIEW IF EXISTS t2;