ES|QL: Make fork available in release builds

docs/changelog/129606.yaml

@@ -0,0 +1,35 @@
+pr: 129606
+summary: Release FORK in tech preview
+area: ES|QL
+type: feature
+issues: []
+highlight:
+  title: Release FORK in tech preview
+  body: |-
+    Fork is a foundational building block that allows multiple branches of execution.
+    Conceptually, fork is:
+    - a bifurcation of the stream, with all data going to each fork branch, followed by
+    - a merge of the branches, enhanced with a discriminator column called FORK:
+
+    Example:
+
+    [source,yaml]
+    ----------------------------
+    FROM test
+    | FORK
+    ( WHERE content:"fox" )
+    ( WHERE content:"dog" )
+    | SORT _fork
+    ----------------------------
+
+    The FORK command add a discriminator column called `_fork`:
+
+    [source,yaml]
+    ----------------------------
+    | id  | content   | _fork |
+    |-----|-----------|-------|
+    | 3   | brown fox | fork1 |
+    | 4   | white dog | fork2 |
+    ----------------------------
+
+  notable: true

x-pack/plugin/esql/qa/testFixtures/src/main/resources/rerank.csv-spec

@@ -96,7 +96,7 @@ book_no:keyword | title:text                                            | author
 
 
 reranker after RRF
-required_capability: fork
+required_capability: fork_v9
 required_capability: rrf
 required_capability: match_operator_colon
 required_capability: rerank

x-pack/plugin/esql/qa/testFixtures/src/main/resources/rrf.csv-spec

@@ -3,7 +3,7 @@
 //
 
 simpleRrf
-required_capability: fork
+required_capability: fork_v9
 required_capability: rrf
 required_capability: match_operator_colon
 
@@ -22,7 +22,7 @@ _score:double | _fork:keyword | emp_no:integer
 ;
 
 rrfWithMatchAndScore
-required_capability: fork
+required_capability: fork_v9
 required_capability: rrf
 required_capability: match_operator_colon
 
@@ -44,7 +44,7 @@ _score:double | _fork:keyword  | _id:keyword
 ;
 
 rrfWithDisjunctionAndPostFilter
-required_capability: fork
+required_capability: fork_v9
 required_capability: rrf
 required_capability: match_operator_colon
 
@@ -66,7 +66,7 @@ _score:double | _fork:keyword  | _id:keyword
 ;
 
 rrfWithStats
-required_capability: fork
+required_capability: fork_v9
 required_capability: rrf
 required_capability: match_operator_colon
 
@@ -86,7 +86,7 @@ count_fork:long | _fork:keyword
 ;
 
 rrfWithMultipleForkBranches
-required_capability: fork
+required_capability: fork_v9
 required_capability: rrf
 required_capability: match_operator_colon
 
@@ -112,6 +112,7 @@ _score:double | author:keyword                    | title:keyword        | _fork
 ;
 
 rrfWithSemanticSearch
+required_capability: fork_v9
 required_capability: rrf
 required_capability: semantic_text_field_caps
 required_capability: metadata_score

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

@@ -32,7 +32,7 @@ public class ForkIT extends AbstractEsqlIntegTestCase {
 
     @Before
     public void setupIndex() {
-        assumeTrue("requires FORK capability", EsqlCapabilities.Cap.FORK.isEnabled());
+        assumeTrue("requires FORK capability", EsqlCapabilities.Cap.FORK_V9.isEnabled());
         createAndPopulateIndices();
     }
 

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

@@ -58,11 +58,11 @@ processingCommand
     | changePointCommand
     | completionCommand
     | sampleCommand
+    | forkCommand
     // in development
     | {this.isDevVersion()}? inlinestatsCommand
     | {this.isDevVersion()}? lookupCommand
     | {this.isDevVersion()}? insistCommand
-    | {this.isDevVersion()}? forkCommand
     | {this.isDevVersion()}? rerankCommand
     | {this.isDevVersion()}? rrfCommand
     ;
@@ -282,7 +282,7 @@ insistCommand
     ;
 
 forkCommand
-    : DEV_FORK forkSubQueries
+    : FORK forkSubQueries
     ;
 
 forkSubQueries

x-pack/plugin/esql/src/main/antlr/lexer/Fork.g4

@@ -9,7 +9,7 @@ lexer grammar Fork;
 //
 // Fork
 //
-DEV_FORK :        {this.isDevVersion()}? 'fork'          -> pushMode(FORK_MODE);
+FORK : 'fork' -> pushMode(FORK_MODE);
 
 mode FORK_MODE;
 // commands needs to break out of their mode and the default mode when they encounter RP

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -917,11 +917,6 @@ public enum Cap {
          */
         AGGREGATE_METRIC_DOUBLE_RENDERING(AGGREGATE_METRIC_DOUBLE_FEATURE_FLAG),
 
-        /**
-         * Support for FORK command
-         */
-        FORK(Build.current().isSnapshot()),
-
         /**
          * Support for RERANK command
          */
@@ -1038,9 +1033,9 @@ public enum Cap {
         MAX_OVER_TIME(Build.current().isSnapshot()),
 
         /**
-         * Support streaming of sub plan results
+         * Support for FORK out of snapshot
          */
-        FORK_V9(Build.current().isSnapshot()),
+        FORK_V9,
 
         /**
          * Support for the {@code leading_zeros} named parameter.