ESQL: Method to convert BooleanBlock to a "mask"

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/ConstantNullBlock.java

@@ -48,6 +48,11 @@ public OrdinalBytesRefBlock asOrdinals() {
         return null;
     }
 
+    @Override
+    public ToMask toMask() {
+        return new ToMask(blockFactory.newConstantBooleanVector(false, positionCount), false);
+    }
+
     @Override
     public boolean isNull(int position) {
         return true;

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/ConstantNullVector.java

@@ -48,6 +48,12 @@ public OrdinalBytesRefVector asOrdinals() {
         throw new UnsupportedOperationException("null vector");
     }
 
+    @Override
+    public ToMask toMask() {
+        assert false : "null vector";
+        throw new UnsupportedOperationException("null vector");
+    }
+
     @Override
     public ConstantNullVector filter(int... positions) {
         assert false : "null vector";

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/ToMask.java

@@ -0,0 +1,22 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.compute.data;
+
+import org.elasticsearch.core.Releasable;
+
+/**
+ * Result from calling {@link BooleanBlock#toMask}. {@link #close closing} this will
+ * close the contained {@link #mask()}. If you want to keep a reference to it then you'll
+ * have to {@link Block#incRef()} it.
+ */
+public record ToMask(BooleanVector mask, boolean hadMultivaluedFields) implements Releasable {
+    @Override
+    public void close() {
+        mask.close();
+    }
+}

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-ArrayBlock.java.st

@@ -101,6 +101,32 @@ $if(BytesRef)$
     public OrdinalBytesRefBlock asOrdinals() {
         return null;
     }
+
+$elseif(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    @Override
+    public ToMask toMask() {
+        if (getPositionCount() == 0) {
+            return new ToMask(blockFactory().newConstantBooleanVector(false, 0), false);
+        }
+        try (BooleanVector.FixedBuilder builder = blockFactory().newBooleanVectorFixedBuilder(getPositionCount())) {
+            boolean hasMv = false;
+            for (int p = 0; p < getPositionCount(); p++) {
+                builder.appendBoolean(switch (getValueCount(p)) {
+                    case 0 -> false;
+                    case 1 -> getBoolean(getFirstValueIndex(p));
+                    default -> {
+                        hasMv = true;
+                        yield false;
+                    }
+                });
+            }
+            return new ToMask(builder.build(), hasMv);
+        }
+    }
 $endif$
 
     @Override

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-ArrayVector.java.st

@@ -130,8 +130,19 @@ $if(BytesRef)$
     public OrdinalBytesRefVector asOrdinals() {
         return null;
     }
-$endif$
 
+$elseif(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    @Override
+    public ToMask toMask() {
+        incRef();
+        return new ToMask(this, false);
+    }
+
+$endif$
 $if(BytesRef)$
     @Override
     public BytesRef getBytesRef(int position, BytesRef dest) {

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-BigArrayBlock.java.st

@@ -86,6 +86,33 @@ public final class $Type$BigArrayBlock extends AbstractArrayBlock implements $Ty
         return null;
     }
 
+$if(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    @Override
+    public ToMask toMask() {
+        if (getPositionCount() == 0) {
+            return new ToMask(blockFactory().newConstantBooleanVector(false, 0), false);
+        }
+        try (BooleanVector.FixedBuilder builder = blockFactory().newBooleanVectorFixedBuilder(getPositionCount())) {
+            boolean hasMv = false;
+            for (int p = 0; p < getPositionCount(); p++) {
+                builder.appendBoolean(switch (getValueCount(p)) {
+                    case 0 -> false;
+                    case 1 -> getBoolean(getFirstValueIndex(p));
+                    default -> {
+                        hasMv = true;
+                        yield false;
+                    }
+                });
+            }
+            return new ToMask(builder.build(), hasMv);
+        }
+    }
+$endif$
+
     @Override
     public $type$ get$Type$(int valueIndex) {
         return vector.get$Type$(valueIndex);

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-BigArrayVector.java.st

@@ -84,6 +84,18 @@ $endif$
         return new $Type$VectorBlock(this);
     }
 
+$if(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    @Override
+    public ToMask toMask() {
+        incRef();
+        return new ToMask(this, false);
+    }
+$endif$
+
     @Override
     public $type$ get$Type$(int position) {
         return values.get(position);

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-Block.java.st

@@ -63,8 +63,15 @@ $if(BytesRef)$
      * returns null. Callers must not release the returned block as no extra reference is retained by this method.
      */
     OrdinalBytesRefBlock asOrdinals();
-$endif$
 
+$elseif(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    ToMask toMask();
+
+$endif$
     @Override
     $Type$Block filter(int... positions);
 

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-ConstantVector.java.st

@@ -59,8 +59,19 @@ $if(BytesRef)$
     public OrdinalBytesRefVector asOrdinals() {
         return null;
     }
-$endif$
 
+$elseif(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    @Override
+    public ToMask toMask() {
+        incRef();
+        return new ToMask(this, false);
+    }
+
+$endif$
     @Override
     public $Type$Vector filter(int... positions) {
         return blockFactory().newConstant$Type$Vector(value, positions.length);

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-Vector.java.st

@@ -51,8 +51,15 @@ $if(BytesRef)$
      * returns null. Callers must not release the returned vector as no extra reference is retained by this method.
      */
     OrdinalBytesRefVector asOrdinals();
-$endif$
 
+$elseif(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    ToMask toMask();
+
+$endif$
     @Override
     $Type$Vector filter(int... positions);
 

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/X-VectorBlock.java.st

@@ -44,8 +44,18 @@ $if(BytesRef)$
             return null;
         }
     }
-$endif$
 
+$elseif(boolean)$
+    /**
+     * Convert this to a {@link BooleanVector "mask"} that's appropriate for
+     * passing to {@link #keepMask}.
+     */
+    @Override
+    public ToMask toMask() {
+        return vector.toMask();
+    }
+
+$endif$
     @Override
 $if(BytesRef)$
     public BytesRef getBytesRef(int valueIndex, BytesRef dest) {