bitflicker64 commented on code in PR #2994:
URL: https://github.com/apache/hugegraph/pull/2994#discussion_r4154106031


##########
hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/traversal/optimize/TraversalUtil.java:
##########
@@ -645,14 +679,553 @@ private static boolean 
extractHasContainers(HugeVertexStep<?> newStep,
 
     private static boolean canExtractHasContainers(HugeGraph graph,
                                                    HasContainerHolder holder) {
-        for (HasContainer has : holder.getHasContainers()) {
+        // Keep unsafe labels and their sibling properties for local filtering.
+        if (hasUnsafeLabelPredicate(holder)) {
+            return false;
+        }
+        List<HasContainer> hasContainers = holder.getHasContainers();
+        for (HasContainer has : hasContainers) {
             if (!canExtractHasContainer(graph, has)) {
                 return false;
             }
         }
         return true;
     }
 
+    private static void prepareLocalHasContainers(
+            Step<?, ?> source, Traversal.Admin<?, ?> traversal) {
+        QueryHolder query = (QueryHolder) source;
+        Step<?, ?> step = source.getNextStep();
+        while (step instanceof HasStep || step instanceof NoOpBarrierStep) {
+            Step<?, ?> next = step.getNextStep();
+            if (step instanceof HasStep) {
+                HasContainerHolder holder = (HasContainerHolder) step;
+                for (HasContainer has : new 
ArrayList<>(holder.getHasContainers())) {
+                    // Paging is query metadata, never an element property 
filter.
+                    if (QueryHolder.SYSPROP_PAGE.equals(has.getKey())) {
+                        query.addHasContainer(has);
+                        holder.removeHasContainer(has);
+                        continue;
+                    }
+                    if (T.id.getAccessor().equals(has.getKey())) {
+                        // ID lookup is complete across labels. Existing source
+                        // IDs and unsupported predicates still filter locally.
+                        if (source instanceof HugeGraphStep &&
+                            GraphStep.processHasContainerIds((HugeGraphStep<?, 
?>) source, has)) {
+                            holder.removeHasContainer(has);
+                            continue;
+                        }
+                        holder.removeHasContainer(has);
+                        holder.addHasContainer(new 
LocalIdHasContainer(has.getPredicate()));
+                        continue;
+                    }
+                    if (T.label.getAccessor().equals(has.getKey())) {
+                        holder.removeHasContainer(has);
+                        HasContainer label = new 
LocalLabelHasContainer(has.getPredicate());
+                        if (source instanceof HugeGraphStep &&
+                            canPushPositiveLabel((HugeGraphStep<?, ?>) source, 
has)) {
+                            // A positive label conjunct uses the label index,
+                            // independent of per-label property index 
coverage.
+                            // Keep the runtime label matcher for source-ID 
queries.
+                            query.addHasContainer(label);
+                        } else {
+                            // Keep unsupported candidates and adjacent-vertex
+                            // labels local, including their paging boundary.
+                            holder.addHasContainer(label);
+                        }
+                        continue;
+                    }
+                    if (keyForContainsKey(has.getKey()) || 
keyForContainsValue(has.getKey())) {
+                        // Backend CONTAINS support varies and source IDs use
+                        // local filtering too. Preserve HugeGraph's map query
+                        // semantics without treating "key"/"value" as names.
+                        holder.removeHasContainer(has);
+                        traversal.addStep(traversal.getSteps().indexOf(step),
+                                          new LocalContainsStep<>(traversal, 
has));
+                        continue;
+                    }
+                    List<P<Object>> predicates = new ArrayList<>();
+                    collectPredicates(predicates, 
ImmutableList.of(has.getPredicate()));
+                    if (predicates.stream().anyMatch(p ->
+                            p.getBiPredicate() == 
Condition.RelationType.TEXT_CONTAINS)) {
+                        // Child traversals can be unbound during optimization;
+                        // the matcher resolves the graph from each runtime 
element.
+                        holder.removeHasContainer(has);
+                        holder.addHasContainer(new LocalSearchHasContainer(
+                                has.getKey(), has.getPredicate()));
+                    }
+                }
+                if (holder.getHasContainers().isEmpty()) {
+                    TraversalHelper.copyLabels(step, step.getPreviousStep(), 
false);
+                    traversal.removeStep(step);
+                }
+            }
+            step = next;
+        }
+        if (query.queryInfo().paging() && step instanceof RangeGlobalStep) {
+            // Bound the raw backend page even when local filters prevent 
normal
+            // range extraction. Keep the range step to apply offset/limit 
after
+            // those filters; a filtered page may contain fewer results.
+            query.setRange(0, ((RangeGlobalStep<?>) step).getHighRange());
+        }
+    }
+
+    private static boolean canPushPositiveLabel(HugeGraphStep<?, ?> source,
+                                                HasContainer has) {
+        if (!isEqInLabelPredicate(has)) {
+            return false;
+        }
+        HugeGraph graph = tryGetGraph(source);
+        if (graph == null) {
+            return false;
+        }
+        List<P<Object>> predicates = new ArrayList<>();
+        collectPredicates(predicates, ImmutableList.of(has.getPredicate()));
+        for (P<Object> predicate : predicates) {
+            Object value = predicate.getValue();
+            BiPredicate<?, ?> bp = predicate.getBiPredicate();
+            if (bp == Contains.within && !(value instanceof Collection)) {
+                return false;
+            }
+            Collection<?> values = bp == Contains.within ?
+                                   (Collection<?>) value : 
Collections.singletonList(value);
+            for (Object candidate : values) {
+                if (!hasLabelIndex(graph, source.returnsVertex(), candidate)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    private static boolean hasLabelIndex(HugeGraph graph, boolean vertex, 
Object value) {
+        if (value instanceof Number) {
+            value = IdGenerator.of(((Number) value).longValue());
+        }
+        try {
+            SchemaLabel label;
+            if (value instanceof Id) {
+                Id id = (Id) value;
+                // Nonpositive IDs include internal schema objects that aren't
+                // user labels. Preserve their local matching behavior.
+                if (!id.number() || id.asLong() <= 0L) {
+                    return false;
+                }
+                label = vertex ? graph.vertexLabel(id) : graph.edgeLabel(id);
+            } else if (value instanceof String) {
+                label = vertex ? graph.vertexLabel((String) value) : 
graph.edgeLabel((String) value);
+            } else {
+                return false;
+            }
+            // Do not turn a working local filter into a missing-label/index 
error.
+            return label != null && label.enableLabelIndex();
+        } catch (IllegalArgumentException | NotFoundException e) {
+            return false;
+        }
+    }
+
+    private static P<?> localIdPredicate(P<?> predicate) {
+        // Keep IDs local to preserve source-ID intersections and step 
ordering.
+        // UUID/Element values need the same representation as 
HugeElement.id(). Leave
+        // strings unchanged so HasContainer retains its string-ID comparison.
+        P<?> copy = predicate.clone();
+        List<P<Object>> leaves = new ArrayList<>();
+        collectPredicates(leaves, ImmutableList.of(copy));
+        for (P<Object> leaf : leaves) {
+            Object value = leaf.getValue();
+            if (value instanceof Collection) {
+                List<Object> values = new ArrayList<>();
+                for (Object item : (Collection<?>) value) {
+                    values.add(localIdValue(item));
+                }
+                leaf.setValue(values);
+            } else {
+                leaf.setValue(localIdValue(value));
+            }
+        }
+        return copy;
+    }
+
+    private static Object localIdValue(Object value) {
+        if (value instanceof UUID || value instanceof Element) {
+            return HugeElement.getIdValue(HugeType.VERTEX, value);
+        }
+        return value;
+    }
+
+    private static final class LocalIdHasContainer extends HasContainer {
+
+        private static final long serialVersionUID = 1L;
+
+        private LocalIdHasContainer(P<?> predicate) {
+            super(T.id.getAccessor(), localIdPredicate(predicate));
+        }
+
+        @Override
+        protected boolean testId(Element element) {
+            return testLocalIdPredicate(this.getPredicate(), element.id());
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    private static boolean testLocalIdPredicate(P<?> predicate, Object id) {
+        if (predicate instanceof ConnectiveP) {
+            boolean and = predicate instanceof AndP;
+            for (P<?> child : ((ConnectiveP<?>) predicate).getPredicates()) {
+                if (testLocalIdPredicate(child, id) != and) {
+                    return !and;
+                }
+            }
+            return and;
+        }
+        Object value = predicate.getValue();
+        Object first = value;
+        if (value instanceof Collection) {
+            Collection<?> values = (Collection<?>) value;
+            first = values.isEmpty() ? null : values.iterator().next();
+        }
+        // HasContainer decides string-ID comparison from only the top-level
+        // P value. ConnectiveP has no such value; decide separately per leaf.
+        Object actual = first instanceof String ? id.toString() : id;
+        return ((BiPredicate<Object, Object>) 
predicate.getBiPredicate()).test(actual, value);
+    }
+
+    private static final class LocalLabelHasContainer extends HasContainer {
+
+        private static final long serialVersionUID = 1L;
+
+        private LocalLabelHasContainer(P<?> predicate) {
+            super(T.label.getAccessor(), predicate.clone());
+        }
+
+        @Override
+        protected boolean testLabel(Element element) {
+            // Resolve against the actual element, not a graph captured while
+            // strategies run. Child traversals may be unbound or later cloned.
+            return testLabelPredicate(this.getPredicate(), ((HugeElement) 
element).schemaLabel());
+        }
+    }
+
+    private static final class LocalContainsStep<S extends Element> extends 
HasStep<S> {
+
+        private static final long serialVersionUID = 1L;
+
+        private LocalContainsStep(Traversal.Admin<?, ?> traversal, 
HasContainer has) {
+            super(traversal, has.clone());
+            E.checkArgument(has.getPredicate().getBiPredicate() == Compare.eq,
+                            "CONTAINS query with relation '%s' is not 
supported",
+                            has.getPredicate().getBiPredicate());
+        }
+
+        @Override
+        protected boolean filter(Traverser.Admin<S> traverser) {
+            HugeElement element = (HugeElement) traverser.get();
+            // Adjacent vertices can be ID/label-only shells. Like 
properties(),
+            // load their properties before evaluating the system property map.
+            element.getFilledProperties();
+            // Keep a HasStep boundary so count/range cannot bypass this 
filter.
+            // Resolve schema from the runtime element; clone/reset must not
+            // retain a graph or transaction captured during optimization.
+            for (HasContainer has : this.getHasContainers()) {
+                boolean matches = keyForContainsKey(has.getKey()) || 
keyForContainsValue(has.getKey()) ?
+                                  convContains2Relation(element.graph(), 
has).test(element) :
+                                  has.test(element);
+                if (!matches) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    private static boolean testLabelPredicate(P<?> predicate, SchemaLabel 
label) {
+        if (predicate instanceof ConnectiveP) {
+            boolean and = predicate instanceof AndP;
+            for (P<?> child : ((ConnectiveP<?>) predicate).getPredicates()) {
+                if (testLabelPredicate(child, label) != and) {
+                    return !and;
+                }
+            }
+            return and;
+        }
+        BiPredicate<?, ?> bp = predicate.getBiPredicate();
+        Object value = predicate.getValue();
+        if (bp == Contains.within || bp == Contains.without) {
+            for (Object item : (Collection<?>) value) {
+                if (testLabelValue(Compare.eq, label, item)) {
+                    return bp == Contains.within;
+                }
+            }
+            return bp == Contains.without;
+        }
+        return testLabelValue((BiPredicate<Object, Object>) bp, label, value);
+    }
+
+    private static boolean testLabelValue(BiPredicate<Object, Object> 
predicate,
+                                          SchemaLabel label, Object value) {
+        if (value instanceof Number) {
+            value = IdGenerator.of(((Number) value).longValue());
+        }
+        return predicate.test(value instanceof Id ? label.id() : label.name(), 
value);
+    }
+
+    private static final class LocalSearchHasContainer extends HasContainer {
+
+        private static final long serialVersionUID = 1L;
+
+        private transient HugeGraph matcherGraph;
+        private transient P<?> matcherPredicate;
+        private transient Predicate<Object> matcher;
+
+        private LocalSearchHasContainer(String key, P<?> predicate) {
+            super(key, predicate.clone());
+        }
+
+        @Override
+        protected boolean testValue(Property property) {
+            // Keep the public P tree intact for strategies, hashing and Java
+            // serialization. Resolve the analyzer from the element's graph,
+            // including after cloning, deserialization or graph rebinding.
+            HugeGraph graph = (HugeGraph) property.element().graph();
+            if (this.matcherGraph != graph ||
+                !samePredicateValues(this.getPredicate(), 
this.matcherPredicate)) {
+                P<?> predicate = this.getPredicate().clone();
+                this.matcher = localSearchMatcher(predicate, graph);
+                this.matcherPredicate = predicate;
+                this.matcherGraph = graph;
+            }
+            return this.matcher.test(property.value());
+        }
+
+        @Override
+        public LocalSearchHasContainer clone() {
+            LocalSearchHasContainer clone = (LocalSearchHasContainer) 
super.clone();
+            clone.matcherGraph = null;
+            clone.matcherPredicate = null;
+            clone.matcher = null;
+            return clone;
+        }
+    }
+
+    private static boolean samePredicateValues(P<?> current, P<?> cached) {
+        // P.equals() compares originalValue, not the value changed by 
setValue().
+        if (cached == null || current.getClass() != cached.getClass()) {
+            return false;
+        }
+        if (current instanceof ConnectiveP) {
+            List<? extends P<?>> children = ((ConnectiveP<?>) 
current).getPredicates();
+            List<? extends P<?>> oldChildren = ((ConnectiveP<?>) 
cached).getPredicates();
+            if (children.size() != oldChildren.size()) {
+                return false;
+            }
+            for (int i = 0; i < children.size(); i++) {
+                if (!samePredicateValues(children.get(i), oldChildren.get(i))) 
{
+                    return false;
+                }
+            }
+            return true;
+        }
+        return current.getBiPredicate().equals(cached.getBiPredicate()) &&
+               Objects.equals(current.getValue(), cached.getValue());
+    }
+
+    @SuppressWarnings("unchecked")
+    private static Predicate<Object> localSearchMatcher(P<?> predicate, 
HugeGraph graph) {
+        if (predicate instanceof ConnectiveP) {
+            List<Predicate<Object>> children = new ArrayList<>();
+            for (P<?> child : ((ConnectiveP<?>) predicate).getPredicates()) {
+                children.add(localSearchMatcher(child, graph));
+            }
+            boolean and = predicate instanceof AndP;
+            return value -> {
+                for (Predicate<Object> child : children) {
+                    if (child.test(value) != and) {
+                        return !and;
+                    }
+                }
+                return and;
+            };
+        }
+        if (predicate.getBiPredicate() != 
Condition.RelationType.TEXT_CONTAINS) {
+            return (P<Object>) predicate;
+        }
+        // Match SEARCH terms in place, preserving range and side-effect 
ordering.
+        return graph.searchPredicate((String) predicate.getValue());
+    }
+
+    private static boolean hasUnsafeLabelInTraversal(
+            Traversal.Admin<?, ?> traversal, Step<?, ?> sourceStep) {
+        // Partial pushdown can lose candidates before local label filtering.
+        // Scan the remaining traversal, its children and each ancestor's
+        // remaining steps for filters on child output. Arbitrary extension
+        // steps don't reliably expose element identity, so stay conservative.
+        // FIXME(#3201): Restore selective pushdown when every candidate 
schema label
+        // has compatible index coverage for extracted property predicates.
+        // Outside proven root and child suffixes, negative labels can disable
+        // property pushdown even across element changes (including ancestors
+        // and unknown extension steps), potentially requiring a full scan.
+        List<Step> steps = traversal.getSteps();
+        int start = 0;
+        while (start < steps.size() && steps.get(start) != sourceStep) {
+            start++;
+        }
+        start++;
+        for (int i = start; i < steps.size(); i++) {
+            Step<?, ?> step = steps.get(i);
+            if (changesCurrentElement(step) &&
+                traversal.getParent() instanceof EmptyStep &&
+                onlyCurrentElementSuffix(steps.subList(i, steps.size()))) {
+                return false;
+            }
+            if (step instanceof HasStep) {
+                HasContainerHolder holder = (HasContainerHolder) step;
+                if (hasUnsafeLabelPredicate(holder)) {
+                    return true;
+                }
+            }
+            if (hasUnsafeLabelInChildren(step)) {
+                return true;
+            }
+        }
+        TraversalParent parent = traversal.getParent();
+        if (parent instanceof Step && !(parent instanceof EmptyStep)) {
+            Step<?, ?> parentStep = (Step<?, ?>) parent;
+            // RepeatStep's until/emit siblings can filter this child's output.
+            // This helper only descends, so revisiting the owning step's 
children
+            // cannot recurse back into this ancestor walk.
+            if (hasUnsafeLabelInChildren(parentStep)) {
+                return true;
+            }
+            return hasUnsafeLabelInTraversal(parentStep.getTraversal(), 
parentStep);
+        }
+        return false;
+    }
+
+    private static boolean changesCurrentElement(Step<?, ?> step) {
+        // Vertex adjacency is a scope boundary for this label fallback, not
+        // proof that a self-loop or later hop cannot return the source.
+        // Preserve the source property query's existing index/error semantics;
+        // complete cross-label property candidates are tracked in #3201.
+        // Edge endpoints can recover the source (outE().outV(), inE().inV(),
+        // bothV()). Do not admit EdgeVertexStep here or in the suffix 
allowlist:
+        // checking only that step is too late if outE() already ended the 
scan.
+        return step instanceof VertexStep || step instanceof PropertiesStep;
+    }
+
+    private static boolean onlyCurrentElementSuffix(List<Step> steps) {
+        for (Step<?, ?> step : steps) {
+            // An allowlist is deliberate: select/path, lambdas, repeat and
+            // extension steps may recover earlier elements. Never infer their
+            // provenance from the output type alone. Check by()-children of
+            // order, dedup and projections below before admitting them.
+            if (!(changesCurrentElement(step) || step instanceof HasStep ||
+                  step instanceof NoOpBarrierStep || step instanceof 
RangeGlobalStep ||
+                  step instanceof IdentityStep || step instanceof NotStep ||
+                  step instanceof AndStep || step instanceof OrStep ||
+                  step instanceof TraversalFilterStep ||
+                  step instanceof DedupGlobalStep || step instanceof 
OrderGlobalStep ||
+                  step instanceof IdStep || step instanceof LabelStep ||
+                  step instanceof PropertyKeyStep || step instanceof 
PropertyMapStep ||
+                  step instanceof PropertyValueStep || step instanceof 
ElementMapStep ||
+                  step instanceof ProjectStep || step instanceof FoldStep ||
+                  step instanceof GroupCountStep ||

Review Comment:
   Important: The allowlist now covers the seven steps from the last round, but 
other common steps that keep or reduce the current traverser are still missing, 
so the source plan still depends on which step ends the traversal. 
`TailGlobalStep`, `IsStep`, `UnfoldStep`, `ConstantStep`, `SampleGlobalStep`, 
`GroupStep`, `AggregateGlobalStep` and `PathFilterStep` (`simplePath()`) all 
fail this check. `hasUnsafeLabelInTraversal()` then keeps scanning past 
`out()`, finds the negative label, and `prepareLocalHasContainers()` leaves the 
source property local.
   
   Evidence, from probes at 2cbd5d71 on JDK 11:
   
   - Plan, with the `TraversalUtilOptimizeTest` helpers and `city` as a TEXT 
key: `has("city","Beijing").out().hasLabel(P.neq("author"))` followed by 
`.limit(5)` or `.valueMap()` gives `HugeGraphStep(Vertex,[city.eq(Beijing)])`. 
Followed by `.tail(1)`, `.values("age").is(P.gt(1))`, `.fold().unfold()`, 
`.constant(1)`, `.sample(2)`, `.group().by(T.label)`, `.aggregate("x")` or 
`.simplePath()`, it gives `HugeGraphStep(vertex,[])` plus a local 
`HasStep([city.eq(Beijing)])`, which is a full vertex scan.
   - Runtime on the memory backend, with the 
`testUnindexedPropertyBeforeNegativeLabel` schema plus one `scanDoc` edge: 
`g.V().has("unindexedProp","x").out().hasLabel(P.neq("scanExcluded"))` throws 
`NoIndexException`. The same query with `.tail(1)`, with `.fold().unfold()`, or 
with `.values("unindexedProp").is("y")` returns a row after a scan.
   
   At the merge base 83ef9f3f, `extractHasContainer()` pushes the source 
containers without looking at later steps, so on master all of these shapes 
keep the source index lookup, and with an unindexed property they raise 
`NoIndexException`. The PR description says ordinary adjacency keeps the source 
query's index plan and missing-index errors and that only select/path/repeat or 
unknown extensions stay conservative, but `tail()`, `is()` and `unfold()` are 
none of those.
   
   Requested change: add the remaining standard steps that cannot make an 
earlier element current again (at least `TailGlobalStep`, `IsStep`, 
`UnfoldStep`, `ConstantStep`, `SampleGlobalStep`, and `GroupStep` with its 
`by()` children checked through the existing recursion), and add `.tail(1)`, 
`.is(...)` and `.fold().unfold()` rows to 
`testLabelAfterElementChangeKeepsSourceIndexPlan` and to the `NoIndexException` 
regression. If adding steps one at a time is not sustainable, an alternative is 
to reject only the steps that can make an earlier element current again 
(select, path and tree, where() on step labels, match(), repeat(), lambda 
steps, and unknown step classes) instead of allowing a fixed list. Whichever 
list stays excluded on purpose, state it in the code comment and in the linked 
note.



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