[DO NOT MERGE] ESQL: PoC for name qualifiers

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

@@ -29,7 +29,11 @@
  *
  */
 public final class Alias extends NamedExpression {
-    public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(NamedExpression.class, "Alias", Alias::new);
+    public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(
+        NamedExpression.class,
+        "Alias",
+        Alias::readFrom
+    );
 
     private final Expression child;
 
@@ -39,44 +43,44 @@ public final class Alias extends NamedExpression {
      */
     private Attribute lazyAttribute;
 
+    /**
+     * Sets the qualifier to {@code null}.
+     * Mostly for tests and convenience wherever qualifiers aren't required.
+     */
     public Alias(Source source, String name, Expression child) {
-        this(source, name, child, null);
+        this(source, null, name, child, null);
     }
 
-    public Alias(Source source, String name, Expression child, @Nullable NameId id) {
-        this(source, name, child, id, false);
+    public Alias(Source source, @Nullable String qualifier, String name, Expression child) {
+        this(source, qualifier, name, child, null);
     }
 
-    public Alias(Source source, String name, Expression child, @Nullable NameId id, boolean synthetic) {
-        super(source, name, singletonList(child), id, synthetic);
-        this.child = child;
+    public Alias(Source source, @Nullable String qualifier, String name, Expression child, @Nullable NameId id) {
+        this(source, qualifier, name, child, id, false);
     }
 
-    @Deprecated
-    /**
-     * Old constructor from when this had a qualifier string. Still needed to not break serialization.
-     */
-    private Alias(Source source, String name, String qualifier, Expression child, @Nullable NameId id, boolean synthetic) {
-        this(source, name, child, id, synthetic);
+    public Alias(Source source, @Nullable String qualifier, String name, Expression child, @Nullable NameId id, boolean synthetic) {
+        super(source, qualifier, name, singletonList(child), id, synthetic);
+        this.child = child;
     }
 
-    public Alias(StreamInput in) throws IOException {
-        this(
-            Source.readFrom((StreamInput & PlanStreamInput) in),
-            in.readString(),
-            in.readOptionalString(),
-            in.readNamedWriteable(Expression.class),
-            NameId.readFrom((StreamInput & PlanStreamInput) in),
-            in.readBoolean()
-        );
+    public static Alias readFrom(StreamInput in) throws IOException {
+        Source source = Source.readFrom((StreamInput & PlanStreamInput) in);
+        String name = in.readString();
+        String qualifier = in.readOptionalString();
+        Expression child = in.readNamedWriteable(Expression.class);
+        NameId id = NameId.readFrom((StreamInput & PlanStreamInput) in);
+        boolean synthetic = in.readBoolean();
+
+        return new Alias(source, qualifier, name, child, id, synthetic);
     }
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         Source.EMPTY.writeTo(out);
         out.writeString(name());
         // We used to write the qualifier here. We can still do if needed in the future.
-        out.writeOptionalString(null);
+        out.writeOptionalString(qualifier());
         out.writeNamedWriteable(child());
         id().writeTo(out);
         out.writeBoolean(synthetic());
@@ -89,16 +93,16 @@ public String getWriteableName() {
 
     @Override
     protected NodeInfo<Alias> info() {
-        return NodeInfo.create(this, Alias::new, name(), child, id(), synthetic());
+        return NodeInfo.create(this, Alias::new, qualifier(), name(), child, id(), synthetic());
     }
 
     public Alias replaceChild(Expression child) {
-        return new Alias(source(), name(), child, id(), synthetic());
+        return new Alias(source(), qualifier(), name(), child, id(), synthetic());
     }
 
     @Override
     public Alias replaceChildren(List<Expression> newChildren) {
-        return new Alias(source(), name(), newChildren.get(0), id(), synthetic());
+        return new Alias(source(), qualifier(), name(), newChildren.get(0), id(), synthetic());
     }
 
     public Expression child() {
@@ -124,20 +128,20 @@ public DataType dataType() {
     public Attribute toAttribute() {
         if (lazyAttribute == null) {
             lazyAttribute = resolved()
-                ? new ReferenceAttribute(source(), name(), dataType(), nullable(), id(), synthetic())
-                : new UnresolvedAttribute(source(), name());
+                ? new ReferenceAttribute(source(), qualifier(), name(), dataType(), nullable(), id(), synthetic())
+                : new UnresolvedAttribute(source(), qualifier(), name());
         }
         return lazyAttribute;
     }
 
     @Override
     public String toString() {
-        return child + " AS " + name() + "#" + id();
+        return child + " AS " + qualifiedName() + "#" + id();
     }
 
     @Override
     public String nodeString() {
-        return child.nodeString() + " AS " + name();
+        return child.nodeString() + " AS " + qualifiedName();
     }
 
     /**

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

@@ -36,16 +36,23 @@ public abstract class Attribute extends NamedExpression {
     // can the attr be null - typically used in JOINs
     private final Nullability nullability;
 
-    public Attribute(Source source, String name, @Nullable NameId id) {
-        this(source, name, Nullability.TRUE, id);
+    public Attribute(Source source, @Nullable String qualifier, String name, @Nullable NameId id) {
+        this(source, qualifier, name, Nullability.TRUE, id);
     }
 
-    public Attribute(Source source, String name, Nullability nullability, @Nullable NameId id) {
-        this(source, name, nullability, id, false);
+    public Attribute(Source source, @Nullable String qualifier, String name, Nullability nullability, @Nullable NameId id) {
+        this(source, qualifier, name, nullability, id, false);
     }
 
-    public Attribute(Source source, String name, Nullability nullability, @Nullable NameId id, boolean synthetic) {
-        super(source, name, emptyList(), id, synthetic);
+    public Attribute(
+        Source source,
+        @Nullable String qualifier,
+        String name,
+        Nullability nullability,
+        @Nullable NameId id,
+        boolean synthetic
+    ) {
+        super(source, qualifier, name, emptyList(), id, synthetic);
         this.nullability = nullability;
     }
 
@@ -70,26 +77,36 @@ public AttributeSet references() {
     }
 
     public Attribute withLocation(Source source) {
-        return Objects.equals(source(), source) ? this : clone(source, name(), dataType(), nullable(), id(), synthetic());
+        return Objects.equals(source(), source) ? this : clone(source, qualifier(), name(), dataType(), nullable(), id(), synthetic());
     }
 
     public Attribute withName(String name) {
-        return Objects.equals(name(), name) ? this : clone(source(), name, dataType(), nullable(), id(), synthetic());
+        return Objects.equals(name(), name) ? this : clone(source(), qualifier(), name, dataType(), nullable(), id(), synthetic());
     }
 
     public Attribute withNullability(Nullability nullability) {
-        return Objects.equals(nullable(), nullability) ? this : clone(source(), name(), dataType(), nullability, id(), synthetic());
+        return Objects.equals(nullable(), nullability)
+            ? this
+            : clone(source(), qualifier(), name(), dataType(), nullability, id(), synthetic());
     }
 
     public Attribute withId(NameId id) {
-        return clone(source(), name(), dataType(), nullable(), id, synthetic());
+        return clone(source(), qualifier(), name(), dataType(), nullable(), id, synthetic());
     }
 
     public Attribute withDataType(DataType type) {
-        return Objects.equals(dataType(), type) ? this : clone(source(), name(), type, nullable(), id(), synthetic());
+        return Objects.equals(dataType(), type) ? this : clone(source(), qualifier(), name(), type, nullable(), id(), synthetic());
     }
 
-    protected abstract Attribute clone(Source source, String name, DataType type, Nullability nullability, NameId id, boolean synthetic);
+    protected abstract Attribute clone(
+        Source source,
+        @Nullable String qualifier,
+        String name,
+        DataType type,
+        Nullability nullability,
+        NameId id,
+        boolean synthetic
+    );
 
     @Override
     public Attribute toAttribute() {
@@ -103,12 +120,12 @@ public int semanticHash() {
 
     @Override
     public boolean semanticEquals(Expression other) {
-        return other instanceof Attribute ? id().equals(((Attribute) other).id()) : false;
+        return other instanceof Attribute otherAttribute && id().equals(otherAttribute.id());
     }
 
     @Override
     protected Expression canonicalize() {
-        return clone(Source.EMPTY, name(), dataType(), nullability, id(), synthetic());
+        return clone(Source.EMPTY, qualifier(), name(), dataType(), nullability, id(), synthetic());
     }
 
     @Override
@@ -125,7 +142,7 @@ protected boolean innerEquals(Object o) {
 
     @Override
     public String toString() {
-        return name() + "{" + label() + (synthetic() ? "$" : "") + "}" + "#" + id();
+        return qualifiedName() + "{" + label() + (synthetic() ? "$" : "") + "}" + "#" + id();
     }
 
     @Override

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

@@ -8,6 +8,7 @@
 package org.elasticsearch.xpack.esql.core.expression;
 
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.core.Nullable;
 import org.elasticsearch.xpack.esql.core.tree.NodeInfo;
 import org.elasticsearch.xpack.esql.core.tree.Source;
 import org.elasticsearch.xpack.esql.core.type.DataType;
@@ -21,7 +22,7 @@
  */
 public class EmptyAttribute extends Attribute {
     public EmptyAttribute(Source source) {
-        super(source, StringUtils.EMPTY, null);
+        super(source, null, StringUtils.EMPTY, null);
     }
 
     @Override
@@ -35,7 +36,15 @@ public String getWriteableName() {
     }
 
     @Override
-    protected Attribute clone(Source source, String name, DataType type, Nullability nullability, NameId id, boolean synthetic) {
+    protected Attribute clone(
+        Source source,
+        @Nullable String qualifier,
+        String name,
+        DataType type,
+        Nullability nullability,
+        NameId id,
+        boolean synthetic
+    ) {
         return this;
     }
 

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

@@ -21,7 +21,7 @@ public final class Expressions {
     private Expressions() {}
 
     public static NamedExpression wrapAsNamed(Expression exp) {
-        return exp instanceof NamedExpression ne ? ne : new Alias(exp.source(), exp.sourceText(), exp);
+        return exp instanceof NamedExpression ne ? ne : new Alias(exp.source(), null, exp.sourceText(), exp);
     }
 
     public static List<Attribute> asAttributes(List<? extends NamedExpression> named) {