[CALCITE-7487] ProjectJoinTransposeRule throws ArrayIndexOutOfBoundsException in PushProjector when a Join input has a zero-column row type

core/src/main/java/org/apache/calcite/rel/rules/PushProjector.java

@@ -457,13 +457,22 @@
         || (childRel instanceof SetOp)) {
       // if nothing is projected from the children, arbitrarily project
       // the first columns; this is necessary since Fennel doesn't
-      // handle 0-column projections
-      if (nProject == 0 && childPreserveExprs.isEmpty()) {
+      // handle 0-column projections.
+      //
+      // An input may legitimately have a zero-column row type: for
+      // example, a Values with an empty row type and a single empty
+      // tuple, which returns one row with zero columns and is the
+      // identity for cross join. There is no first column to fall back
+      // on in that case, so skip the workaround rather than set a bit
+      // that points past the input's fields; createProjectRefsAndExprs
+      // would use it to index into an empty field list.
+      if (nProject == 0 && childPreserveExprs.isEmpty() && nFields > 0) {
         projRefs.set(0);
         nProject = 1;
       }
       if (childRel instanceof Join) {
-        if (nRightProject == 0 && rightPreserveExprs.isEmpty()) {
+        if (nRightProject == 0 && rightPreserveExprs.isEmpty()
+            && nFieldsRight > 0) {
           projRefs.set(nFields);
           nRightProject = 1;
         }

core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java

@@ -1559,6 +1559,56 @@ private void checkSemiOrAntiJoinProjectTranspose(JoinRelType type) {
     checkJoinProjectTransposeDoesNotMatch(JoinRelType.LEFT_MARK);
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7487">[CALCITE-7487]
+   * ProjectJoinTransposeRule throws ArrayIndexOutOfBoundsException in
+   * PushProjector when a Join input has a zero-column row type</a>. */
+  @Test void testProjectJoinTransposeWithZeroColumnRightInput() {
+    relFn(b -> zeroColumnJoinInputRelFn(b, false))
+        .withRule(CoreRules.PROJECT_JOIN_TRANSPOSE).check();
+  }
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7487">[CALCITE-7487]
+   * ProjectJoinTransposeRule throws ArrayIndexOutOfBoundsException in
+   * PushProjector when a Join input has a zero-column row type</a>. */
+  @Test void testProjectJoinTransposeWithZeroColumnLeftInput() {
+    relFn(b -> zeroColumnJoinInputRelFn(b, true))
+        .withRule(CoreRules.PROJECT_JOIN_TRANSPOSE).check();
+  }
+
+  /** Builds {@code Project(CAST(col1))} over a cross join in which one input is
+   * DEE -- a {@link org.apache.calcite.rel.core.Values} with an empty row type,
+   * the identity for cross join. The project must be non-identity, otherwise
+   * {@link RelBuilder} collapses it away and the rule never fires. */
+  private static RelNode zeroColumnJoinInputRelFn(RelBuilder b,
+      boolean deeOnLeft) {
+    final RelDataTypeFactory typeFactory = b.getTypeFactory();
+    final RelDataType bigintType =
+        typeFactory.createSqlType(SqlTypeName.BIGINT);
+    final RelNode nonEmpty = b
+        .values(
+            ImmutableList.of(
+                ImmutableList.of(
+                    (RexLiteral) b.getRexBuilder().makeZeroLiteral(bigintType))),
+            typeFactory.builder().add("col1", bigintType).build())
+        .build();
+    final RelNode dee = b
+        .values(ImmutableList.of(ImmutableList.of()),
+            typeFactory.builder().build())
+        .build();
+    final RelDataType varcharType =
+        typeFactory.createSqlType(SqlTypeName.VARCHAR);
+    return b
+        .push(deeOnLeft ? dee : nonEmpty)
+        .push(deeOnLeft ? nonEmpty : dee)
+        .join(JoinRelType.INNER, b.literal(true))
+        // DEE contributes no fields, so the sole column is at index 0
+        // whichever side it is on.
+        .project(b.getRexBuilder().makeCast(varcharType, b.field(0)))
+        .build();
+  }
+
   /** A SEMI, ANTI or LEFT_MARK join does not project its right input, so
    * {@link JoinProjectTransposeRule} must not pull projects above it. */
   private void checkJoinProjectTransposeDoesNotMatch(JoinRelType type) {

core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml

@@ -12359,6 +12359,44 @@ LogicalProject(DEPTNO=[$0])
     LogicalAggregate(group=[{}], DUMMY=[COUNT()])
       LogicalProject(EMPNO=[$0])
         LogicalTableScan(table=[[scott, EMP]])
+]]>
+    </Resource>
+  </TestCase>
+  <TestCase name="testProjectJoinTransposeWithZeroColumnLeftInput">
+    <Resource name="planBefore">
+      <![CDATA[
+LogicalProject(col1=[CAST($0):VARCHAR NOT NULL])
+  LogicalJoin(condition=[true], joinType=[inner])
+    LogicalValues(tuples=[[{  }]])
+    LogicalValues(tuples=[[{ 0 }]])
+]]>
+    </Resource>
+    <Resource name="planAfter">
+      <![CDATA[
+LogicalJoin(condition=[true], joinType=[inner])
+  LogicalProject
+    LogicalValues(tuples=[[{  }]])
+  LogicalProject(col1=[CAST($0):VARCHAR NOT NULL])
+    LogicalValues(tuples=[[{ 0 }]])
+]]>
+    </Resource>
+  </TestCase>
+  <TestCase name="testProjectJoinTransposeWithZeroColumnRightInput">
+    <Resource name="planBefore">
+      <![CDATA[
+LogicalProject(col1=[CAST($0):VARCHAR NOT NULL])
+  LogicalJoin(condition=[true], joinType=[inner])
+    LogicalValues(tuples=[[{ 0 }]])
+    LogicalValues(tuples=[[{  }]])
+]]>
+    </Resource>
+    <Resource name="planAfter">
+      <![CDATA[
+LogicalJoin(condition=[true], joinType=[inner])
+  LogicalProject(col1=[CAST($0):VARCHAR NOT NULL])
+    LogicalValues(tuples=[[{ 0 }]])
+  LogicalProject
+    LogicalValues(tuples=[[{  }]])
 ]]>
     </Resource>
   </TestCase>