Script: ulong via fields API

Exposes unsigned long via the fields API.

Unsigned longs default to java signed longs.  That means the upper range
appears negative.  Consumers should use `Long.compareUnsigned(long, long)`
`Long.divideUnsigned(long, long)` and `Long.remainderUnsigned(long, long)`
to correctly work with values known to be unsigned long.

Alternatively, users may treat the unsigned long type as `BigInteger` using
the field API, `field('ul').as(Field.BigInteger).getValue(BigInteger.ZERO)`.
```
field('ul').as(Field.BigInteger).getValue(BigInteger.valueOf(1000))
field('ul').getValue(1000L)
```

This change also implements the beginning of the converters for the fields
API.  The following conversions have been added:
```
ulong <-> BigInteger
long <-> BigInteger
double -> BigInteger
String (parsed as long or double) -> BigInteger
double -> long
String (parsed as long or double) -> long
Date (epoch milliseconds) -> long
Nano Date (epoch nanoseconds) -> long
boolean (1L for true, 0L for false) -> long
```

Fixes: elastic#64361

Author: stu-elastic

modules/lang-painless/src/main/resources/org/elasticsearch/painless/org.elasticsearch.script.fields.txt

@@ -10,10 +10,18 @@
 
 # API
 class org.elasticsearch.script.Field {
+  org.elasticsearch.script.Converter BigInteger
+  org.elasticsearch.script.Converter Long
   String getName()
   boolean isEmpty()
   List getValues()
   def getValue(def)
+  double getDouble(double)
+  long getLong(long)
+  org.elasticsearch.script.Field as(org.elasticsearch.script.Converter)
+}
+
+class org.elasticsearch.script.Converter {
 }
 
 class org.elasticsearch.script.DocBasedScript {

server/src/main/java/org/elasticsearch/index/fielddata/ScriptDocValues.java

@@ -17,6 +17,9 @@
 import org.elasticsearch.common.geo.GeoUtils;
 import org.elasticsearch.common.time.DateUtils;
 import org.elasticsearch.geometry.utils.Geohash;
+import org.elasticsearch.script.Field;
+import org.elasticsearch.script.FieldValues;
+import org.elasticsearch.script.InvalidConversion;
 import org.elasticsearch.script.JodaCompatibleZonedDateTime;
 
 import java.io.IOException;
@@ -25,6 +28,8 @@
 import java.util.AbstractList;
 import java.util.Arrays;
 import java.util.Comparator;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
 import java.util.function.UnaryOperator;
 
 /**
@@ -35,7 +40,7 @@
  * return as a single {@link ScriptDocValues} instance can be reused to return
  * values form multiple documents.
  */
-public abstract class ScriptDocValues<T> extends AbstractList<T> {
+public abstract class ScriptDocValues<T> extends AbstractList<T> implements FieldValues<T> {
 
     /**
      * Set the current doc ID.
@@ -68,6 +73,31 @@ public final void sort(Comparator<? super T> c) {
         throw new UnsupportedOperationException("doc values are unmodifiable");
     }
 
+    public abstract Field<T> toField(String fieldName);
+
+    public List<T> getValues() {
+        return this;
+    }
+
+    public T getNonPrimitiveValue() {
+        return get(0);
+    }
+
+    public long getLongValue() {
+        throw new InvalidConversion(this.getClass(), long.class);
+    }
+
+    public double getDoubleValue() {
+        throw new InvalidConversion(this.getClass(), double.class);
+    }
+
+    protected void throwIfEmpty() {
+        if (size() == 0) {
+            throw new IllegalStateException("A document doesn't have a value for a field! " +
+                "Use doc[<field>].size()==0 to check if a document is missing a field!");
+        }
+    }
+
     public static final class Longs extends ScriptDocValues<Long> {
         private final SortedNumericDocValues in;
         private long[] values = new long[0];
@@ -107,17 +137,31 @@ public long getValue() {
 
         @Override
         public Long get(int index) {
-            if (count == 0) {
-                throw new IllegalStateException("A document doesn't have a value for a field! " +
-                    "Use doc[<field>].size()==0 to check if a document is missing a field!");
-            }
+            throwIfEmpty();
             return values[index];
         }
 
         @Override
         public int size() {
             return count;
         }
+
+        @Override
+        public long getLongValue() {
+            throwIfEmpty();
+            return values[0];
+        }
+
+        @Override
+        public double getDoubleValue() {
+            throwIfEmpty();
+            return values[0];
+        }
+
+        @Override
+        public Field<Long> toField(String fieldName) {
+            return new Field.LongField(fieldName, this);
+        }
     }
 
     public static final class Dates extends ScriptDocValues<JodaCompatibleZonedDateTime> {
@@ -192,6 +236,29 @@ void refreshArray() throws IOException {
                 }
             }
         }
+
+        @Override
+        public long getLongValue() {
+            throwIfEmpty();
+            Instant dt = dates[0].toInstant();
+            if (isNanos) {
+                return TimeUnit.SECONDS.toNanos(dt.getEpochSecond()) + dt.getNano();
+            }
+            return dt.toEpochMilli();
+        }
+
+        @Override
+        public double getDoubleValue() {
+            return getLongValue();
+        }
+
+        @Override
+        public Field<JodaCompatibleZonedDateTime> toField(String fieldName) {
+            if (isNanos) {
+                return new Field.DateNanosField(fieldName, this);
+            }
+            return new Field.DateMillisField(fieldName, this);
+        }
     }
 
     public static final class Doubles extends ScriptDocValues<Double> {
@@ -246,6 +313,22 @@ public Double get(int index) {
         public int size() {
             return count;
         }
+
+        @Override
+        public long getLongValue() {
+            return (long) getDoubleValue();
+        }
+
+        @Override
+        public double getDoubleValue() {
+            throwIfEmpty();
+            return values[0];
+        }
+
+        @Override
+        public Field<Double> toField(String fieldName) {
+            return new Field.DoubleField(fieldName, this);
+        }
     }
 
     public abstract static class Geometry<T> extends ScriptDocValues<T> {
@@ -436,6 +519,11 @@ public double getMercatorHeight() {
         public GeoBoundingBox getBoundingBox() {
           return size() == 0 ? null : boundingBox;
         }
+
+        @Override
+        public Field<GeoPoint> toField(String fieldName) {
+            return new Field.GeoPointField(fieldName, this);
+        }
     }
 
     public static final class Booleans extends ScriptDocValues<Boolean> {
@@ -496,6 +584,22 @@ private static boolean[] grow(boolean[] array, int minSize) {
                 return array;
         }
 
+        @Override
+        public long getLongValue() {
+            throwIfEmpty();
+            return values[0] ? 1L : 0L;
+        }
+
+        @Override
+        public double getDoubleValue() {
+            throwIfEmpty();
+            return values[0] ? 1.0D : 0.0D;
+        }
+
+        @Override
+        public Field<Boolean> toField(String fieldName) {
+            return new Field.BooleanField(fieldName, this);
+        }
     }
 
     abstract static class BinaryScriptDocValues<T> extends ScriptDocValues<T> {
@@ -568,6 +672,21 @@ protected String bytesToString(BytesRef bytes) {
         public final String getValue() {
             return get(0);
         }
+
+        @Override
+        public long getLongValue() {
+            return Long.parseLong(get(0));
+        }
+
+        @Override
+        public double getDoubleValue() {
+            return Double.parseDouble(get(0));
+        }
+
+        @Override
+        public Field<String> toField(String fieldName) {
+            return new Field.StringField(fieldName, this);
+        }
     }
 
     public static final class BytesRefs extends BinaryScriptDocValues<BytesRef> {
@@ -594,5 +713,9 @@ public BytesRef getValue() {
             return get(0);
         }
 
+        @Override
+        public Field<BytesRef> toField(String fieldName) {
+            return new Field.BytesRefField(fieldName, this);
+        }
     }
 }

server/src/main/java/org/elasticsearch/index/mapper/IpFieldMapper.java

@@ -355,6 +355,11 @@ public String get(int index) {
             public int size() {
                 return count;
             }
+
+            @Override
+            public org.elasticsearch.script.Field<String> toField(String fieldName) {
+                return new org.elasticsearch.script.Field.IpField(fieldName, this);
+            }
         }
 
         @Override

server/src/main/java/org/elasticsearch/script/Converter.java

@@ -0,0 +1,15 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.script;
+
+public interface Converter<CT, CF extends Field<CT>> {
+    CF convert(Field<?> sourceField);
+    Class<CF> getFieldClass();
+    Class<CT> getTargetClass();
+}