better error msg

Author: jan-elastic

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/parser/LogicalPlanBuilder.java

@@ -445,7 +445,9 @@ public PlanFactory visitEnrichCommand(EsqlBaseParser.EnrichCommandContext ctx) {
     public PlanFactory visitChangePointCommand(EsqlBaseParser.ChangePointCommandContext ctx) {
         Source src = source(ctx);
         NamedExpression value = visitQualifiedName(ctx.value);
-        NamedExpression key = ctx.key == null ? new UnresolvedAttribute(src, "@timestamp") : visitQualifiedName(ctx.key);
+        NamedExpression key = ctx.key == null
+            ? new UnresolvedAttribute(src, "@timestamp", "Key column unspecified and default [@timestamp] is missing")
+            : visitQualifiedName(ctx.key);
         Attribute targetType = new ReferenceAttribute(
             src,
             ctx.targetType == null ? "type" : visitQualifiedName(ctx.targetType).name(),

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/VerifierTests.java

@@ -2021,8 +2021,10 @@ public void testChangePoint() {
         var airports = AnalyzerTestUtils.analyzer(loadMapping("mapping-airports.json", "airports"));
         assertEquals("1:30: Unknown column [blahblah]", error("FROM airports | CHANGE_POINT blahblah ON scalerank", airports));
         assertEquals("1:43: Unknown column [blahblah]", error("FROM airports | CHANGE_POINT scalerank ON blahblah", airports));
-        // TODO: nicer error message for missing default column "@timestamp"
-        assertEquals("1:17: Unknown column [@timestamp]", error("FROM airports | CHANGE_POINT scalerank", airports));
+        assertEquals(
+            "1:17: Key column unspecified and default [@timestamp] is missing",
+            error("FROM airports | CHANGE_POINT scalerank", airports)
+        );
     }
 
     public void testChangePoint_keySortable() {