ESQL: Entirely remove META FUNCTIONS (#113967) (#114342)

This removes the undocumented `META FUNCTIONS` command that emits
descriptions for all functions. This shouldn't be used because we never
told anyone about it. I'd have preferred if we'd have explicitly
documented it as no public or if we'd have left it snapshot-only. But
sometimes you make a mistake. I'm hopeful no one is relying on it. It
was never reliable and not public.....

build-tools-internal/src/main/resources/changelog-schema.json

@@ -284,6 +284,7 @@
         "Cluster and node setting",
         "Command line tool",
         "CRUD",
+        "ES|QL",
         "Index setting",
         "Ingest",
         "JVM option",

docs/changelog/113967.yaml

@@ -0,0 +1,13 @@
+pr: 113967
+summary: "ESQL: Entirely remove META FUNCTIONS"
+area: ES|QL
+type: breaking
+issues: []
+breaking:
+  title: "ESQL: Entirely remove META FUNCTIONS"
+  area: ES|QL
+  details: |
+    Removes an undocumented syntax from ESQL: META FUNCTION. This was never
+    reliable or really useful. Consult the documentation instead.
+  impact: "Removes an undocumented syntax from ESQL: META FUNCTION"
+  notable: false

docs/reference/rest-api/usage.asciidoc

@@ -239,8 +239,7 @@ GET /_xpack/usage
       "keep" : 0,
       "enrich" : 0,
       "from" : 0,
-      "row" : 0,
-      "meta" : 0
+      "row" : 0
     },
     "queries" : {
       "rest" : {

x-pack/plugin/build.gradle

@@ -202,5 +202,6 @@ tasks.named("precommit").configure {
 tasks.named("yamlRestTestV7CompatTransform").configure({ task ->
   task.skipTest("security/10_forbidden/Test bulk response with invalid credentials", "warning does not exist for compatibility")
   task.skipTest("inference/inference_crud/Test get all", "Assertions on number of inference models break due to default configs")
+  task.skipTest("esql/60_usage/Basic ESQL usage output (telemetry)", "The telemetry output changed. We dropped a column. That's safe.")
 })
 

x-pack/plugin/esql/qa/server/mixed-cluster/src/javaRestTest/java/org/elasticsearch/xpack/esql/qa/mixed/MixedClusterEsqlSpecIT.java

@@ -72,10 +72,6 @@ public MixedClusterEsqlSpecIT(
     protected void shouldSkipTest(String testName) throws IOException {
         super.shouldSkipTest(testName);
         assumeTrue("Test " + testName + " is skipped on " + bwcVersion, isEnabled(testName, instructions, bwcVersion));
-        assumeFalse(
-            "Skip META tests on mixed version clusters because we change it too quickly",
-            testCase.requiredCapabilities.contains("meta")
-        );
         if (mode == ASYNC) {
             assumeTrue("Async is not supported on " + bwcVersion, supportsAsync());
         }

x-pack/plugin/esql/qa/server/multi-clusters/src/javaRestTest/java/org/elasticsearch/xpack/esql/ccq/MultiClusterSpecIT.java

@@ -112,10 +112,6 @@ protected void shouldSkipTest(String testName) throws IOException {
         );
         assumeFalse("INLINESTATS not yet supported in CCS", testCase.requiredCapabilities.contains("inlinestats"));
         assumeFalse("INLINESTATS not yet supported in CCS", testCase.requiredCapabilities.contains("inlinestats_v2"));
-        assumeFalse(
-            "Skip META tests on mixed version clusters because we change it too quickly",
-            testCase.requiredCapabilities.contains("meta")
-        );
     }
 
     private TestFeatureService remoteFeaturesService() throws IOException {

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/EsqlActionIT.java

@@ -34,7 +34,6 @@
 import org.elasticsearch.xpack.core.esql.action.ColumnInfo;
 import org.elasticsearch.xpack.esql.VerificationException;
 import org.elasticsearch.xpack.esql.core.type.DataType;
-import org.elasticsearch.xpack.esql.expression.function.EsqlFunctionRegistry;
 import org.elasticsearch.xpack.esql.parser.ParsingException;
 import org.elasticsearch.xpack.esql.plugin.EsqlPlugin;
 import org.junit.Before;
@@ -1038,29 +1037,6 @@ public void testShowInfo() {
         }
     }
 
-    public void testMetaFunctions() {
-        try (EsqlQueryResponse results = run("meta functions")) {
-            assertThat(
-                results.columns(),
-                equalTo(
-                    List.of(
-                        new ColumnInfoImpl("name", "keyword"),
-                        new ColumnInfoImpl("synopsis", "keyword"),
-                        new ColumnInfoImpl("argNames", "keyword"),
-                        new ColumnInfoImpl("argTypes", "keyword"),
-                        new ColumnInfoImpl("argDescriptions", "keyword"),
-                        new ColumnInfoImpl("returnType", "keyword"),
-                        new ColumnInfoImpl("description", "keyword"),
-                        new ColumnInfoImpl("optionalArgs", "boolean"),
-                        new ColumnInfoImpl("variadic", "boolean"),
-                        new ColumnInfoImpl("isAggregation", "boolean")
-                    )
-                )
-            );
-            assertThat(getValuesList(results).size(), equalTo(new EsqlFunctionRegistry().listFunctions().size()));
-        }
-    }
-
     public void testInWithNullValue() {
         try (EsqlQueryResponse results = run("from test | where null in (data, 2) | keep data")) {
             assertThat(results.columns(), equalTo(List.of(new ColumnInfoImpl("data", "long"))));

x-pack/plugin/esql/src/main/antlr/EsqlBaseLexer.g4

@@ -66,7 +66,6 @@ FROM : 'from'                 -> pushMode(FROM_MODE);
 GROK : 'grok'                 -> pushMode(EXPRESSION_MODE);
 KEEP : 'keep'                 -> pushMode(PROJECT_MODE);
 LIMIT : 'limit'               -> pushMode(EXPRESSION_MODE);
-META : 'meta'                 -> pushMode(META_MODE);
 MV_EXPAND : 'mv_expand'       -> pushMode(MVEXPAND_MODE);
 RENAME : 'rename'             -> pushMode(RENAME_MODE);
 ROW : 'row'                   -> pushMode(EXPRESSION_MODE);
@@ -467,26 +466,6 @@ SHOW_WS
     : WS -> channel(HIDDEN)
     ;
 
-//
-// META commands
-//
-mode META_MODE;
-META_PIPE : PIPE -> type(PIPE), popMode;
-
-FUNCTIONS : 'functions';
-
-META_LINE_COMMENT
-    : LINE_COMMENT -> channel(HIDDEN)
-    ;
-
-META_MULTILINE_COMMENT
-    : MULTILINE_COMMENT -> channel(HIDDEN)
-    ;
-
-META_WS
-    : WS -> channel(HIDDEN)
-    ;
-
 mode SETTING_MODE;
 SETTING_CLOSING_BRACKET : CLOSING_BRACKET -> type(CLOSING_BRACKET), popMode;