[refactor] Refactor the predicate position() optimisation into a Quer…

…yRewriter

exist-core/src/main/java/org/exist/xquery/Optimizer.java

@@ -80,8 +80,14 @@ public class Optimizer extends DefaultExpressionVisitor {
 
     public Optimizer(XQueryContext context) {
         this.context = context;
+        final List<QueryRewriter> defaultRewriters = List.of(
+                new PositionalPredicateRewriter(context)
+        );
+        this.rewriters = new ArrayList<>(defaultRewriters);
         final DBBroker broker = context.getBroker();
-        this.rewriters = broker != null ? broker.getIndexController().getQueryRewriters(context) : Collections.emptyList();
+        if (broker != null) {
+            rewriters.addAll(broker.getIndexController().getQueryRewriters(context));
+        }
     }
 
     public boolean hasOptimized() {
@@ -169,37 +175,6 @@ public void visitLocationStep(final LocationStep locationStep) {
         }
     }
 
-    /**
-     * Test whether we can optimise position() withing a predicate to a POSITIONAL version of a predicate.
-     *
-     * @param predicate the predicate to test
-     *
-     * @return the inner expr to be replaced and the literal value to replace it with if it can be optimised, null otherwise.
-     */
-    private @Nullable Tuple2<Expression, LiteralValue> canOptimizeToPositionalPredicate(final Predicate predicate) {
-        if (predicate.getSubExpressionCount() == 1) {
-            final Expression predInnerExpr = predicate.getSubExpression(0);
-            if (predInnerExpr instanceof final ValueComparison valueComparison && valueComparison.getRelation() == Constants.Comparison.EQ) {
-                final Expression left = valueComparison.getLeft();
-                final Expression right = valueComparison.getRight();
-
-                if (left instanceof final InternalFunctionCall leftInternalFunctionCall && leftInternalFunctionCall.getFunction() instanceof FunPosition
-                        && right instanceof final LiteralValue rightLiteralValue && rightLiteralValue.returnsType() == Type.INTEGER) {
-
-                    // NOTE(AR) if the predicate is like [position() eq 1] or [position() = 1] then we could rewrite it to [1]
-                    return Tuple(predInnerExpr, rightLiteralValue);
-
-                } else if (left instanceof final LiteralValue leftLiteralValue && leftLiteralValue.returnsType() == Type.INTEGER
-                        && right instanceof final InternalFunctionCall rightInternalFunctionCall && rightInternalFunctionCall.getFunction() instanceof FunPosition) {
-
-                    // NOTE(AR) if the predicate is like [1 eq position()]  or [1 = position()] then we could rewrite it to [1]
-                    return Tuple(predInnerExpr, leftLiteralValue);
-                }
-            }
-        }
-        return null;
-    }
-
     @Override
     public void visitFilteredExpr(final FilteredExpression filtered) {
         super.visitFilteredExpr(filtered);
@@ -345,30 +320,6 @@ public void visitGeneralComparison(GeneralComparison comparison) {
 
     public void visitPredicate(Predicate predicate) {
         ++predicates;
-
-        // NOTE(AR) try and optimise position() withing a predicate to a POSITIONAL version of a predicate
-        @Nullable final Tuple2<Expression, LiteralValue> predOptimizableInnerExpr = canOptimizeToPositionalPredicate(predicate);
-        if (predOptimizableInnerExpr != null) {
-            try {
-                // Replace the predicates expression with a literal number
-
-                predicate.replace(predOptimizableInnerExpr._1, predOptimizableInnerExpr._2);
-
-                // traverse to outermost predicate and then call analyze! to make sure execution mode is correct
-                Expression parentExpr = predicate;
-                Predicate outermostPredicate = predicate;
-                while ((parentExpr = parentExpr.getParent()) != null) {
-                    if (parentExpr instanceof final Predicate parentPredicate) {
-                        outermostPredicate = parentPredicate;
-                    }
-                }
-                outermostPredicate.analyze(new AnalyzeContextInfo(outermostPredicate.getParent(), 0));
-
-            } catch (final XPathException e) {
-                LOG.warn("Failed to optimize expression within predicate: {}: {}", predOptimizableInnerExpr, e.getMessage(), e);
-            }
-        }
-
         super.visitPredicate(predicate);
         --predicates;
     }

exist-core/src/main/java/org/exist/xquery/PositionalPredicateRewriter.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2014, Evolved Binary Ltd
+ */
+package org.exist.xquery;
+
+import com.evolvedbinary.j8fu.tuple.Tuple2;
+import org.exist.xquery.functions.fn.FunPosition;
+import org.exist.xquery.value.Type;
+
+import javax.annotation.Nullable;
+
+import static com.evolvedbinary.j8fu.tuple.Tuple.Tuple;
+
+/**
+ * Rewrite position() withing a predicate to a POSITIONAL version of the predicate where possible.
+ *
+ * @author <a href="mailto:adam@evolvedbinary.com">Adam Retter</a>
+ */
+public class PositionalPredicateRewriter extends QueryRewriter {
+
+    public PositionalPredicateRewriter(final XQueryContext context) {
+        super(context);
+    }
+
+    @Override
+    public Pragma rewriteLocationStep(final LocationStep locationStep) throws XPathException {
+
+        @Nullable final Predicate[] predicates = locationStep.getPredicates();
+        if (predicates != null) {
+            for (final Predicate predicate : predicates) {
+                @Nullable final Tuple2<Expression, LiteralValue> predicateOptimizableInnerExpr = canOptimizeToPositionalPredicate(predicate);
+                if (predicateOptimizableInnerExpr != null) {
+                    predicate.replace(predicateOptimizableInnerExpr._1, predicateOptimizableInnerExpr._2);
+                }
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Test whether we can optimise position() withing a predicate to a POSITIONAL version of a predicate.
+     *
+     * @param predicate the predicate to test
+     *
+     * @return the inner expr to be replaced and the literal value to replace it with if it can be optimised, null otherwise.
+     */
+    private @Nullable Tuple2<Expression, LiteralValue> canOptimizeToPositionalPredicate(final Predicate predicate) {
+        if (predicate.getSubExpressionCount() == 1) {
+            final org.exist.xquery.Expression predInnerExpr = predicate.getSubExpression(0);
+            if (predInnerExpr instanceof final ValueComparison valueComparison && valueComparison.getRelation() == Constants.Comparison.EQ) {
+                final org.exist.xquery.Expression left = valueComparison.getLeft();
+                final org.exist.xquery.Expression right = valueComparison.getRight();
+
+                if (left instanceof final InternalFunctionCall leftInternalFunctionCall && leftInternalFunctionCall.getFunction() instanceof FunPosition
+                        && right instanceof final org.exist.xquery.LiteralValue rightLiteralValue && rightLiteralValue.returnsType() == Type.INTEGER) {
+
+                    // NOTE(AR) if the predicate is like [position() eq 1] or [position() = 1] then we could rewrite it to [1]
+                    return Tuple(predInnerExpr, rightLiteralValue);
+
+                } else if (left instanceof final org.exist.xquery.LiteralValue leftLiteralValue && leftLiteralValue.returnsType() == Type.INTEGER
+                        && right instanceof final InternalFunctionCall rightInternalFunctionCall && rightInternalFunctionCall.getFunction() instanceof FunPosition) {
+
+                    // NOTE(AR) if the predicate is like [1 eq position()]  or [1 = position()] then we could rewrite it to [1]
+                    return Tuple(predInnerExpr, leftLiteralValue);
+                }
+            }
+        }
+        return null;
+    }
+}