Remove partiallyFoldable code as it is not needed

Author: julian-elastic

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

@@ -85,13 +85,6 @@ public boolean foldable() {
         return false;
     }
 
-    /**
-     * Whether the expression can be evaluated partially, for example we might be able to fold and expression in an argument of the function but not remove the function completely
-     */
-    public boolean partiallyFoldable() {
-        return false;
-    }
-
     /**
      * Evaluate this expression statically to a constant. It is an error to call
      * this if {@link #foldable} returns false.
@@ -102,10 +95,6 @@ public Object fold(FoldContext ctx) {
         throw new QlIllegalArgumentException("Should not fold expression");
     }
 
-    public Expression partiallyFold(FoldContext ctx) {
-        throw new QlIllegalArgumentException("Should not fold expression");
-    }
-
     public abstract Nullability nullable();
 
     // the references/inputs/leaves of the expression tree

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/vector/Knn.java

@@ -18,7 +18,6 @@
 import org.elasticsearch.xpack.esql.common.Failures;
 import org.elasticsearch.xpack.esql.core.InvalidArgumentException;
 import org.elasticsearch.xpack.esql.core.expression.Expression;
-import org.elasticsearch.xpack.esql.core.expression.FoldContext;
 import org.elasticsearch.xpack.esql.core.expression.Literal;
 import org.elasticsearch.xpack.esql.core.expression.MapExpression;
 import org.elasticsearch.xpack.esql.core.expression.TypeResolutions;
@@ -248,28 +247,6 @@ private Map<String, Object> knnQueryOptions() throws InvalidArgumentException {
         return matchOptions;
     }
 
-    @Override
-    public boolean partiallyFoldable() {
-        return true;
-    }
-
-    @Override
-    public Expression partiallyFold(FoldContext ctx) {
-        if (k instanceof Literal) {
-            // already folded, return self
-            return this;
-        }
-        Object foldedK = k.fold(ctx);
-        if (foldedK instanceof Number == false) {
-            throw new EsqlIllegalArgumentException(format(null, "K value must be a constant integer in [{}], found [{}]", source(), k()));
-        }
-        List<Expression> newChildren = new ArrayList<>(this.children());
-        newChildren.set(2, new Literal(source(), foldedK, INTEGER));
-        Expression replaced = this.replaceChildren(newChildren);
-        log.error("Partially folded knn function [{}] with k value [{}]", replaced, foldedK);
-        return replaced;
-    }
-
     @Override
     public List<Number> queryAsObject() {
         // we need to check that we got a list and every element in the list is a number

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/ConstantFolding.java

@@ -19,11 +19,6 @@ public ConstantFolding() {
 
     @Override
     public Expression rule(Expression e, LogicalOptimizerContext ctx) {
-        if (e.foldable()) {
-            return Literal.of(ctx.foldCtx(), e);
-        } else if (e.partiallyFoldable()) {
-            return e.partiallyFold(ctx.foldCtx());
-        }
-        return e;
+        return e.foldable() ? Literal.of(ctx.foldCtx(), e) : e;
     }
 }