From b927aac70d7dfd9112201344077f0a65998a74b2 Mon Sep 17 00:00:00 2001
From: Shaik Sher Ali <sher_shaik@apple.com>
Date: Thu, 2 Nov 2023 22:01:00 -0700
Subject: [PATCH] misc(query): make match[] parameter optional for LabelNames
 queries (#1687)

---
 .../MultiPartitionPlannerSpec.scala           | 23 +++++++++++++++++++
 .../filodb/prometheus/parse/Parser.scala      | 14 +++++++----
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/coordinator/src/test/scala/filodb.coordinator/queryplanner/MultiPartitionPlannerSpec.scala b/coordinator/src/test/scala/filodb.coordinator/queryplanner/MultiPartitionPlannerSpec.scala
index a2de722611..2f47ddf533 100644
--- a/coordinator/src/test/scala/filodb.coordinator/queryplanner/MultiPartitionPlannerSpec.scala
+++ b/coordinator/src/test/scala/filodb.coordinator/queryplanner/MultiPartitionPlannerSpec.scala
@@ -1337,6 +1337,29 @@ class MultiPartitionPlannerSpec extends AnyFunSpec with Matchers with PlanValida
       .children(0).asInstanceOf[LabelNamesExec].endMs shouldEqual (endSeconds * 1000)
   }
 
+  it("should materialize LabelNames with empty query correctly") {
+    val (startSeconds: Int, endSeconds: Int, engine: MultiPartitionPlanner) = getPlannerForMetadataQueryTests
+
+    val promQl = """"""
+    val lv = Parser.labelNamesQueryToLogicalPlan(promQl, TimeStepParams(startSeconds, step, endSeconds))
+
+    val promQlQueryParams = PromQlQueryParams(promQl, startSeconds, step, endSeconds, Some("/api/v2/labels/name"))
+    val execPlan = engine.materialize(lv, QueryContext(origQueryParams = promQlQueryParams, plannerParams =
+      PlannerParams(processMultiPartition = true)))
+
+    execPlan.isInstanceOf[LabelNamesDistConcatExec] shouldEqual true
+    execPlan.children.size shouldEqual 2
+
+    val expectedUrlParams = Map("match[]" -> "{}")
+    execPlan.children(1).asInstanceOf[MetadataRemoteExec].urlParams shouldEqual (expectedUrlParams)
+    execPlan.children(1).asInstanceOf[MetadataRemoteExec].queryContext.origQueryParams.asInstanceOf[PromQlQueryParams].
+      endSecs shouldEqual (localPartitionStart - 1)
+    execPlan.children(0).asInstanceOf[LabelNamesDistConcatExec]
+      .children(0).asInstanceOf[LabelNamesExec].startMs shouldEqual (localPartitionStart * 1000)
+    execPlan.children(0).asInstanceOf[LabelNamesDistConcatExec]
+      .children(0).asInstanceOf[LabelNamesExec].endMs shouldEqual (endSeconds * 1000)
+  }
+
   it ("should generate correct plan for multipartition BinaryJoin with instant function") {
     def partitions(timeRange: TimeRange): List[PartitionAssignment] = List(PartitionAssignment("remote", "remote-url",
       TimeRange(timeRange.startMs, timeRange.endMs)))
diff --git a/prometheus/src/main/scala/filodb/prometheus/parse/Parser.scala b/prometheus/src/main/scala/filodb/prometheus/parse/Parser.scala
index f6bde99cef..3fb870e0bd 100644
--- a/prometheus/src/main/scala/filodb/prometheus/parse/Parser.scala
+++ b/prometheus/src/main/scala/filodb/prometheus/parse/Parser.scala
@@ -5,7 +5,7 @@ import com.typesafe.scalalogging.StrictLogging
 import filodb.core.GlobalConfig
 import filodb.core.query.{ColumnFilter, Filter, QueryConfig, QueryUtils}
 import filodb.prometheus.ast._
-import filodb.query.{LabelValues, LogicalPlan}
+import filodb.query.{LabelNames, LabelValues, LogicalPlan}
 
 /**
   * Parser routes requests to LegacyParser or AntlrParser.
@@ -169,10 +169,14 @@ object Parser extends StrictLogging {
 
   def labelNamesQueryToLogicalPlan(query: String,
                                    timeParams: TimeRangeParams): LogicalPlan = {
-    val expression = parseQuery(query)
-    expression match {
-      case p: InstantExpression => p.toLabelNamesPlan(timeParams)
-      case _ => throw new UnsupportedOperationException()
+    if (query == null || query.isEmpty) {
+      LabelNames(Seq.empty, timeParams.start * 1000, timeParams.end * 1000)
+    } else {
+      val expression = parseQuery(query)
+      expression match {
+        case p: InstantExpression => p.toLabelNamesPlan(timeParams)
+        case _ => throw new UnsupportedOperationException()
+      }
     }
   }