From ec2581435442dca0a07b9b34fe717559c5f3ea9c Mon Sep 17 00:00:00 2001
From: Wan Kai <wankai123@foxmail.com>
Date: Tue, 28 Mar 2023 11:04:52 +0800
Subject: [PATCH] Support parse PromQL expression has empty labels in the
 braces for metadata query. (#10599)

---
 docs/en/changes/changes.md                    |  1 +
 .../promql/rt/grammar/PromQLParser.g4         |  2 +-
 .../rt/parser/PromQLMatchVisitorTest.java     | 47 +++++++++++++++----
 3 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/docs/en/changes/changes.md b/docs/en/changes/changes.md
index 55498f22b1..38073edeb5 100644
--- a/docs/en/changes/changes.md
+++ b/docs/en/changes/changes.md
@@ -20,6 +20,7 @@
 * [Breaking Change] Support cross-thread trace profiling. The data structure and query APIs are changed.
 * Fix PromQL HTTP API `/api/v1/labels` response missing `service` label.
 * Fix possible NPE when initialize `IntList`.
+* Support parse PromQL expression has empty labels in the braces for metadata query.
 
 #### UI
 * Revert: cpm5d function. This feature is cancelled from backend.
diff --git a/oap-server/server-query-plugin/promql-plugin/src/main/antlr4/org/apache/skywalking/promql/rt/grammar/PromQLParser.g4 b/oap-server/server-query-plugin/promql-plugin/src/main/antlr4/org/apache/skywalking/promql/rt/grammar/PromQLParser.g4
index ae29a801e0..3d0abf8485 100644
--- a/oap-server/server-query-plugin/promql-plugin/src/main/antlr4/org/apache/skywalking/promql/rt/grammar/PromQLParser.g4
+++ b/oap-server/server-query-plugin/promql-plugin/src/main/antlr4/org/apache/skywalking/promql/rt/grammar/PromQLParser.g4
@@ -36,7 +36,7 @@ mulDivMod:       MUL | DIV | MOD;
 compare:        (DEQ | NEQ | LTE | LT | GTE | GT) BOOL?;
 
 metricName:      NAME_STRING;
-metricInstant:   metricName | metricName L_BRACE labelList R_BRACE;
+metricInstant:   metricName | metricName L_BRACE labelList? R_BRACE;
 metricRange:     metricInstant L_BRACKET DURATION R_BRACKET;
 
 labelName:       NAME_STRING;
diff --git a/oap-server/server-query-plugin/promql-plugin/src/test/java/org/apache/skywalking/promql/rt/parser/PromQLMatchVisitorTest.java b/oap-server/server-query-plugin/promql-plugin/src/test/java/org/apache/skywalking/promql/rt/parser/PromQLMatchVisitorTest.java
index e4becc6643..232c4c4801 100644
--- a/oap-server/server-query-plugin/promql-plugin/src/test/java/org/apache/skywalking/promql/rt/parser/PromQLMatchVisitorTest.java
+++ b/oap-server/server-query-plugin/promql-plugin/src/test/java/org/apache/skywalking/promql/rt/parser/PromQLMatchVisitorTest.java
@@ -18,6 +18,8 @@
 
 package org.apache.skywalking.promql.rt.parser;
 
+import java.util.Arrays;
+import java.util.Collection;
 import org.antlr.v4.runtime.CharStreams;
 import org.antlr.v4.runtime.CommonTokenStream;
 import org.antlr.v4.runtime.tree.ParseTree;
@@ -27,20 +29,49 @@ import org.apache.skywalking.oap.query.promql.rt.result.ParseResultType;
 import org.apache.skywalking.promql.rt.grammar.PromQLLexer;
 import org.apache.skywalking.promql.rt.grammar.PromQLParser;
 import org.junit.jupiter.api.Assertions;
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
 
 public class PromQLMatchVisitorTest {
-    @Test
-    public void testMatchVisitor() {
-        PromQLLexer lexer = new PromQLLexer(
-            CharStreams.fromString("service_cpm{service='serviceA', layer='GENERAL'}"));
+
+    public static Collection<Object[]> data() {
+        return Arrays.asList(new Object[][] {
+            {
+                "service_cpm",
+                ParseResultType.MATCH,
+                "service_cpm",
+                0
+            },
+            {
+                "service_cpm{}",
+                ParseResultType.MATCH,
+                "service_cpm",
+                0
+            },
+            {
+                "service_cpm{service='serviceA', layer='GENERAL'}",
+                ParseResultType.MATCH,
+                "service_cpm",
+                2
+            }
+        });
+    }
+
+    @ParameterizedTest
+    @MethodSource("data")
+    public void testMatchVisitor(
+        String expression,
+        ParseResultType wantType,
+        String metricName,
+        int labelsSize) {
+        PromQLLexer lexer = new PromQLLexer(CharStreams.fromString(expression));
         CommonTokenStream tokens = new CommonTokenStream(lexer);
         PromQLParser parser = new PromQLParser(tokens);
         ParseTree tree = parser.expression();
         PromQLMatchVisitor visitor = new PromQLMatchVisitor();
         MatcherSetResult parseResult = visitor.visit(tree);
-        Assertions.assertEquals(ParseResultType.MATCH, parseResult.getResultType());
-        Assertions.assertEquals("service_cpm", parseResult.getMetricName());
-        Assertions.assertEquals(2, parseResult.getLabelMap().size());
+        Assertions.assertEquals(wantType, parseResult.getResultType());
+        Assertions.assertEquals(metricName, parseResult.getMetricName());
+        Assertions.assertEquals(labelsSize, parseResult.getLabelMap().size());
     }
 }