Improve error message for unsupported window functions in eventstats/streamstats

api/src/test/java/org/opensearch/sql/api/UnifiedQueryPlannerTest.java

@@ -165,10 +165,11 @@ public void unsupportedWindowFunctionIsRethrownAsSemanticCheckException() {
     // CalciteRexNodeVisitor#visitWindowFunction's
     // orElseThrow. The throw site emits CalciteUnsupportedException so this path normalizes to a
     // 4xx SemanticCheckException rather than escaping as a 500.
-    givenInvalidQuery("source = catalog.employees | eventstats rank()")
+    givenInvalidQuery("source = catalog.employees | eventstats percent_rank()")
         .assertErrorType(SemanticCheckException.class)
         .assertCauseType(CalciteUnsupportedException.class)
-        .assertErrorMessageContains("Unexpected window function: rank");
+        .assertErrorMessageContains(
+            "Window function 'percent_rank' is not supported in eventstats/streamstats");
   }
 
   @Test

core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java

@@ -705,7 +705,14 @@ public RexNode visitWindowFunction(WindowFunction node, CalcitePlanContext conte
                       node.getWindowFrame());
             })
         .orElseThrow(
-            () -> new CalciteUnsupportedException("Unexpected window function: " + funcName));
+            () ->
+                new CalciteUnsupportedException(
+                    "Window function '"
+                        + funcName
+                        + "' is not supported in eventstats/streamstats."
+                        + " Supported functions: avg, count, dc, distinct_count, earliest,"
+                        + " latest, max, min, row_number, stddev_pop, stddev_samp, sum,"
+                        + " var_pop, var_samp."));
   }
 
   private List<RexNode> translateOrderKeys(

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalcitePPLEventstatsIT.java

@@ -12,6 +12,7 @@
 import java.util.List;
 import org.json.JSONObject;
 import org.junit.jupiter.api.Test;
+import org.opensearch.sql.common.antlr.SyntaxCheckException;
 import org.opensearch.sql.ppl.PPLIntegTestCase;
 
 public class CalcitePPLEventstatsIT extends PPLIntegTestCase {
@@ -329,7 +330,23 @@ public void testUnsupportedWindowFunctions() {
                   executeQuery(
                       String.format(
                           "source=%s | eventstats %s(age)", TEST_INDEX_STATE_COUNTRY, u)));
-      verifyErrorMessageContains(e, "Unexpected window function: " + u);
+      verifyErrorMessageContains(e, "is not supported in eventstats/streamstats");
+    }
+  }
+
+  @Test
+  public void testRankingWindowFunctionsUnsupportedInEventstats() {
+    // rank/dense_rank aren't in eventstats/streamstats' windowFunctionName grammar rule, so this
+    // is now a parse-time rejection rather than a semantic one.
+    for (String func : List.of("rank", "dense_rank")) {
+      Throwable e =
+          assertThrowsWithReplace(
+              SyntaxCheckException.class,
+              () ->
+                  executeQuery(
+                      String.format(
+                          "source=%s | eventstats %s() by state", TEST_INDEX_STATE_COUNTRY, func)));
+      verifyErrorMessageContains(e, "is not a valid term at this part of the query");
     }
   }
 

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalciteStreamstatsCommandIT.java

@@ -16,6 +16,7 @@
 import org.json.JSONObject;
 import org.junit.jupiter.api.Test;
 import org.opensearch.client.Request;
+import org.opensearch.sql.common.antlr.SyntaxCheckException;
 import org.opensearch.sql.ppl.PPLIntegTestCase;
 import org.opensearch.sql.util.RequiresCapability;
 
@@ -846,7 +847,24 @@ public void testUnsupportedWindowFunctions() {
                   executeQuery(
                       String.format(
                           "source=%s | streamstats %s(age)", TEST_INDEX_STATE_COUNTRY, u)));
-      verifyErrorMessageContains(e, "Unexpected window function: " + u);
+      verifyErrorMessageContains(e, "is not supported in eventstats/streamstats");
+    }
+  }
+
+  @Test
+  public void testRankingWindowFunctionsUnsupportedInStreamstats() {
+    // rank/dense_rank aren't in eventstats/streamstats' windowFunctionName grammar rule, so this
+    // is now a parse-time rejection rather than a semantic one.
+    for (String func : List.of("rank", "dense_rank")) {
+      Throwable e =
+          assertThrowsWithReplace(
+              SyntaxCheckException.class,
+              () ->
+                  executeQuery(
+                      String.format(
+                          "source=%s | streamstats %s() by state",
+                          TEST_INDEX_STATE_COUNTRY, func)));
+      verifyErrorMessageContains(e, "is not a valid term at this part of the query");
     }
   }
 

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -832,8 +832,6 @@ windowFunctionName
 
 scalarWindowFunctionName
    : ROW_NUMBER
-   | RANK
-   | DENSE_RANK
    | PERCENT_RANK
    | CUME_DIST
    | FIRST