add ability to know if an attribute is a metric

Author: not-napoleon

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

@@ -154,4 +154,9 @@ public static boolean dataTypeEquals(List<Attribute> left, List<Attribute> right
      * @return true if the attribute represents a TSDB dimension type
      */
     public abstract boolean isDimension();
+
+    /**
+     * @return true if the attribute represents a TSDB metric type
+     */
+    public abstract boolean isMetric();
 }

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

@@ -49,6 +49,11 @@ public boolean isDimension() {
         return false;
     }
 
+    @Override
+    public boolean isMetric() {
+        return false;
+    }
+
     @Override
     public boolean resolved() {
         return true;

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

@@ -221,6 +221,11 @@ public boolean isDimension() {
         return field.getTimeSeriesFieldType() == EsField.TimeSeriesFieldType.DIMENSION;
     }
 
+    @Override
+    public boolean isMetric() {
+        return field.getTimeSeriesFieldType() == EsField.TimeSeriesFieldType.METRIC;
+    }
+
     public EsField field() {
         return field;
     }

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

@@ -122,6 +122,13 @@ protected String label() {
 
     @Override
     public boolean isDimension() {
+        // Metadata attributes cannot be dimensions. I think?
+        return false;
+    }
+
+    @Override
+    public boolean isMetric() {
+        // Metadata attributes definitely cannot be metrics.
         return false;
     }
 

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

@@ -122,4 +122,9 @@ protected String label() {
     public boolean isDimension() {
         return false;
     }
+
+    @Override
+    public boolean isMetric() {
+        return false;
+    }
 }

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

@@ -112,6 +112,11 @@ public boolean isDimension() {
         return false;
     }
 
+    @Override
+    public boolean isMetric() {
+        return false;
+    }
+
     @Override
     public String nodeString() {
         return toString();