ESQL: introduce mapping-unavailable fields grammar

docs/changelog/138889.yaml

@@ -0,0 +1,5 @@
+pr: 138889
+summary: Introduce mapping-unavailable fields grammar
+area: ES|QL
+type: feature
+issues: []

x-pack/plugin/esql-core/src/main/java/org/elasticsearch/xpack/esql/core/expression/Expressions.java

@@ -147,10 +147,6 @@ public static Attribute attribute(Expression e) {
         return null;
     }
 
-    public static boolean isPresent(NamedExpression e) {
-        return e instanceof EmptyAttribute == false;
-    }
-
     public static boolean equalsAsAttribute(Expression left, Expression right) {
         if (left.semanticEquals(right) == false) {
             Attribute l = attribute(left);

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

@@ -102,15 +102,15 @@ rerankField
     ;
 
 fromCommand
-    : FROM indexPatternAndMetadataFields
+    : FROM indexPatternAndFields
     ;
 
 timeSeriesCommand
-    : TS indexPatternAndMetadataFields
+    : TS indexPatternAndFields
     ;
 
-indexPatternAndMetadataFields
-    : indexPatternOrSubquery (COMMA indexPatternOrSubquery)* metadata?
+indexPatternAndFields
+    : indexPatternOrSubquery (COMMA indexPatternOrSubquery)* fieldsClause*
     ;
 
 indexPatternOrSubquery
@@ -145,10 +145,24 @@ indexString
     | QUOTED_STRING
     ;
 
-metadata
+fieldsClause
+    : metadataFields
+    | optionalFields
+    | unmappedFields
+    ;
+
+metadataFields
     : METADATA UNQUOTED_SOURCE (COMMA UNQUOTED_SOURCE)*
     ;
 
+optionalFields
+    : OPTIONAL fieldNamePatterns
+    ;
+
+unmappedFields
+    : UNMAPPED fieldNamePatterns
+    ;
+
 evalCommand
     : EVAL fields
     ;
@@ -180,24 +194,34 @@ qualifiedNamePattern
     ;
 
 fieldNamePattern
-    : (identifierPattern (DOT identifierPattern)*)
+    : (identifierPatternOrParameter (DOT identifierPatternOrParameter)*)
     ;
 
 qualifiedNamePatterns
     : qualifiedNamePattern (COMMA qualifiedNamePattern)*
     ;
 
-identifier
-    : UNQUOTED_IDENTIFIER
-    | QUOTED_IDENTIFIER
+fieldNamePatterns
+    : fieldNamePattern (COMMA fieldNamePattern)*
+    ;
+
+identifierOrParameter
+    : identifier
+    | parameter
+    | doubleParameter
     ;
 
-identifierPattern
+identifierPatternOrParameter
     : ID_PATTERN
     | parameter
     | doubleParameter
     ;
 
+identifier
+    : UNQUOTED_IDENTIFIER
+    | QUOTED_IDENTIFIER
+    ;
+
 parameter
     : PARAM                        #inputParam
     | NAMED_OR_POSITIONAL_PARAM    #inputNamedOrPositionalParam
@@ -208,12 +232,6 @@ doubleParameter
     | NAMED_OR_POSITIONAL_DOUBLE_PARAMS    #inputNamedOrPositionalDoubleParams
     ;
 
-identifierOrParameter
-    : identifier
-    | parameter
-    | doubleParameter
-    ;
-
 stringOrParameter
     : string
     | parameter