Fix post-merge compilation and test failures

- Add OPTIONAL_ANY to PPLOperandTypes for BaseConversionUDF
- Revert registerExternalOperator to HEAD's simpler version (origin/main
  used PPLTypeChecker/CalciteFuncSignature not available on this branch)
- Remove duplicate TOSTRING registerOperator (conflicts with custom register)
- Update streamstats and timechart test expectations for sort/hint changes

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java

@@ -28,6 +28,10 @@ public class PPLOperandTypes {
   private PPLOperandTypes() {}
 
   public static final UDFOperandMetadata NONE = UDFOperandMetadata.wrap(OperandTypes.family());
+  public static final UDFOperandMetadata OPTIONAL_ANY =
+      UDFOperandMetadata.wrap(
+          (CompositeOperandTypeChecker)
+              OperandTypes.family(SqlTypeFamily.ANY).or(OperandTypes.family()));
 
   public static final UDFOperandMetadata OPTIONAL_INTEGER =
       UDFOperandMetadata.wrap(OperandTypes.INTEGER.or(OperandTypes.family()));

core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java

@@ -401,16 +401,11 @@ private PPLFuncImpTable(Builder builder, AggBuilder aggBuilder) {
    * @param operator a SqlOperator representing an externally implemented function
    */
   public void registerExternalOperator(BuiltinFunctionName functionName, SqlOperator operator) {
-    PPLTypeChecker typeChecker =
-        wrapSqlOperandTypeChecker(
-            operator.getOperandTypeChecker(),
-            functionName.name(),
-            operator instanceof SqlUserDefinedFunction);
-    CalciteFuncSignature signature = new CalciteFuncSignature(functionName.getName(), typeChecker);
-    externalFunctionRegistry.put(
-        functionName,
-        List.of(
-            Pair.of(signature, (FunctionImp) (builder, args) -> builder.makeCall(operator, args))));
+    if (externalFunctionRegistry.containsKey(functionName)) {
+      logger.warn(
+          String.format(Locale.ROOT, "Function %s is registered multiple times", functionName));
+    }
+    externalFunctionRegistry.put(functionName, (builder, args) -> builder.makeCall(operator, args));
   }
 
   /**
@@ -760,7 +755,6 @@ void populate() {
 
       registerOperator(INTERNAL_PATTERN_PARSER, PPLBuiltinOperators.PATTERN_PARSER);
       registerOperator(TONUMBER, PPLBuiltinOperators.TONUMBER);
-      registerOperator(TOSTRING, PPLBuiltinOperators.TOSTRING);
 
       // Register PPL Convert command functions
       registerOperator(AUTO, PPLBuiltinOperators.AUTO);

ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStreamstatsTest.java

@@ -237,15 +237,15 @@ public void testStreamstatsWithReverse() {
             + "  LogicalSort(sort0=[$8], dir0=[DESC])\n"
             + "    LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4],"
             + " SAL=[$5], COMM=[$6], DEPTNO=[$7], __stream_seq__=[$8], max(SAL)=[MAX($5) OVER"
-            + " (PARTITION BY $7 ROWS UNBOUNDED PRECEDING)])\n"
+            + " (PARTITION BY $7 ORDER BY $0 NULLS LAST ROWS UNBOUNDED PRECEDING)])\n"
             + "      LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4],"
             + " SAL=[$5], COMM=[$6], DEPTNO=[$7], __stream_seq__=[ROW_NUMBER() OVER ()])\n"
             + "        LogicalTableScan(table=[[scott, EMP]])\n";
     verifyLogical(root, expectedLogical);
 
     String expectedSparkSql =
         "SELECT `EMPNO`, `ENAME`, `JOB`, `MGR`, `HIREDATE`, `SAL`, `COMM`, `DEPTNO`,"
-            + " MAX(`SAL`) OVER (PARTITION BY `DEPTNO` ROWS BETWEEN UNBOUNDED"
+            + " MAX(`SAL`) OVER (PARTITION BY `DEPTNO` ORDER BY `EMPNO` NULLS LAST ROWS BETWEEN UNBOUNDED"
             + " PRECEDING AND CURRENT ROW) `max(SAL)`\n"
             + "FROM (SELECT `EMPNO`, `ENAME`, `JOB`, `MGR`, `HIREDATE`, `SAL`, `COMM`, `DEPTNO`,"
             + " ROW_NUMBER() OVER () `__stream_seq__`\n"

ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLTimechartTest.java

@@ -396,7 +396,7 @@ public void testTimechartWithReverse() {
     verifyLogical(root, expectedLogical);
 
     String expectedSparkSql =
-        "SELECT SPAN(`@timestamp`, 1, 'm') `@timestamp`, COUNT(*) `count()`\n"
+        "SELECT\n/*+ `AGG_ARGS`(`ignoreNullBucket` = 'true') */\nSPAN(`@timestamp`, 1, 'm') `@timestamp`, COUNT(*) `count()`\n"
             + "FROM `scott`.`events`\n"
             + "WHERE `@timestamp` IS NOT NULL\n"
             + "GROUP BY SPAN(`@timestamp`, 1, 'm')\n"
@@ -422,7 +422,7 @@ public void testTimechartWithCustomTimefieldAndReverse() {
     verifyLogical(root, expectedLogical);
 
     String expectedSparkSql =
-        "SELECT SPAN(`created_at`, 1, 'M') `created_at`, COUNT(*) `count()`\n"
+        "SELECT\n/*+ `AGG_ARGS`(`ignoreNullBucket` = 'true') */\nSPAN(`created_at`, 1, 'M') `created_at`, COUNT(*) `count()`\n"
             + "FROM `scott`.`events`\n"
             + "WHERE `created_at` IS NOT NULL\n"
             + "GROUP BY SPAN(`created_at`, 1, 'M')\n"