SQL: allow LEFT and RIGHT as function names (elastic#32066)

Due to the way ANTLR works, any declared tokens need to be accounted for
manually inside function names (otherwise a different rule gets applied).

Fix elastic#32046

(cherry picked from commit 20ea72e)

Author: costin

x-pack/plugin/sql/src/main/antlr/SqlBase.g4

@@ -243,7 +243,12 @@ functionExpression
     ;
     
 functionTemplate
-    : identifier '(' (setQuantifier? expression (',' expression)*)? ')'
+    : functionName '(' (setQuantifier? expression (',' expression)*)? ')'
+    ;
+functionName
+    : LEFT 
+    | RIGHT 
+    | identifier
     ;
     
 constant

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/ExpressionBuilder.java

@@ -396,8 +396,7 @@ public Function visitExtractExpression(ExtractExpressionContext ctx) {
     @Override
     public Function visitFunctionExpression(FunctionExpressionContext ctx) {
         FunctionTemplateContext template = ctx.functionTemplate();
-
-        String name = visitIdentifier(template.identifier());
+        String name = template.functionName().getText();
         boolean isDistinct = template.setQuantifier() != null && template.setQuantifier().DISTINCT() != null;
         UnresolvedFunction.ResolutionType resolutionType =
                 isDistinct ? UnresolvedFunction.ResolutionType.DISTINCT : UnresolvedFunction.ResolutionType.STANDARD;

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/SqlBaseBaseListener.java

@@ -803,6 +803,18 @@ class SqlBaseBaseListener implements SqlBaseListener {
    * <p>The default implementation does nothing.</p>
    */
   @Override public void exitFunctionTemplate(SqlBaseParser.FunctionTemplateContext ctx) { }
+  /**
+   * {@inheritDoc}
+   *
+   * <p>The default implementation does nothing.</p>
+   */
+  @Override public void enterFunctionName(SqlBaseParser.FunctionNameContext ctx) { }
+  /**
+   * {@inheritDoc}
+   *
+   * <p>The default implementation does nothing.</p>
+   */
+  @Override public void exitFunctionName(SqlBaseParser.FunctionNameContext ctx) { }
   /**
    * {@inheritDoc}
    *

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/SqlBaseBaseVisitor.java

@@ -473,6 +473,13 @@ class SqlBaseBaseVisitor<T> extends AbstractParseTreeVisitor<T> implements SqlBa
    * {@link #visitChildren} on {@code ctx}.</p>
    */
   @Override public T visitFunctionTemplate(SqlBaseParser.FunctionTemplateContext ctx) { return visitChildren(ctx); }
+  /**
+   * {@inheritDoc}
+   *
+   * <p>The default implementation returns the result of calling
+   * {@link #visitChildren} on {@code ctx}.</p>
+   */
+  @Override public T visitFunctionName(SqlBaseParser.FunctionNameContext ctx) { return visitChildren(ctx); }
   /**
    * {@inheritDoc}
    *

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/SqlBaseListener.java

@@ -745,6 +745,16 @@ interface SqlBaseListener extends ParseTreeListener {
    * @param ctx the parse tree
    */
   void exitFunctionTemplate(SqlBaseParser.FunctionTemplateContext ctx);
+  /**
+   * Enter a parse tree produced by {@link SqlBaseParser#functionName}.
+   * @param ctx the parse tree
+   */
+  void enterFunctionName(SqlBaseParser.FunctionNameContext ctx);
+  /**
+   * Exit a parse tree produced by {@link SqlBaseParser#functionName}.
+   * @param ctx the parse tree
+   */
+  void exitFunctionName(SqlBaseParser.FunctionNameContext ctx);
   /**
    * Enter a parse tree produced by the {@code nullLiteral}
    * labeled alternative in {@link SqlBaseParser#constant}.