add test

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/QueryPlanConstraints.scala

@@ -23,14 +23,18 @@ import org.apache.spark.sql.catalyst.expressions._
 trait QueryPlanConstraints { self: LogicalPlan =>
 
   /**
-   * An [[ExpressionSet]] that contains invariants about the rows output by this operator. For
-   * example, if this set contains the expression `a = 2` then that expression is guaranteed to
-   * evaluate to `true` for all rows produced.
-   */
+    * An [[ExpressionSet]] that contains an additional set of constraints about equality constraints
+    * and `isNotNull` constraints.
+    */
   lazy val allConstraints: ExpressionSet = ExpressionSet(validConstraints
     .union(inferAdditionalConstraints(validConstraints))
     .union(constructIsNotNullConstraints(validConstraints)))
 
+  /**
+    * An [[ExpressionSet]] that contains invariants about the rows output by this operator. For
+    * example, if this set contains the expression `a = 2` then that expression is guaranteed to
+    * evaluate to `true` for all rows produced.
+    */
   lazy val constraints: ExpressionSet = {
     if (conf.constraintPropagationEnabled) {
       ExpressionSet(allConstraints.filter { c =>

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/InferFiltersFromConstraintsSuite.scala

@@ -192,4 +192,17 @@ class InferFiltersFromConstraintsSuite extends PlanTest {
 
     comparePlans(Optimize.execute(original.analyze), correct.analyze)
   }
+
+  test("single left-semi join: filter out nulls on either side on equi-join keys") {
+    val x = testRelation.subquery('x)
+    val y = testRelation.subquery('y)
+    val originalQuery = x.join(y, LeftSemi,
+      condition = Some("x.a".attr === "y.a".attr)).analyze
+    val left = x.where(IsNotNull('a))
+    val right = y.where(IsNotNull('a))
+    val correctAnswer = left.join(right, LeftSemi, condition = Some("x.a".attr === "y.a".attr))
+        .analyze
+    val optimized = Optimize.execute(originalQuery)
+    comparePlans(optimized, correctAnswer)
+  }
 }