MB-27666: Fix nested mode handling for field-implicit queries

[CascadingRadium]

• Fix nested-mode search for field-implicit queries (match_all, docID): These queries previously filtered nested documents at the searcher level, but since ExtractFields returned no fields, the nested collector was never activated. In compound queries (e.g., Boolean filters), this caused a level mismatch—searcher filtering vs nested-level execution—resulting in zero matches.
• Unify filtering at collector level: Introduced HasID() and HasAll() flags in FieldSet to track field-implicit queries. Removed searcher-level filtering from MatchAllSearcher.
• Nested collector now correctly activates, ensuring consistent behavior regardless of query composition.
• Fix an edge case where usage of match_all query as a sub-clause in a NestedConjunctionSearcher could cause a panic.
• Fix a case where root document fields would get excluded from the _all field even when included.
• Fix outdated information in hierarchy.md
• Add unit tests for Hierarchical Nested Vector Search.

[Copilot]

Pull request overview

This PR fixes a critical bug in nested-mode search where field-agnostic queries (match_all, docID) were incorrectly filtered at the searcher level instead of the collector level. The issue caused zero matches when these queries were used in compound queries (e.g., Boolean filters) due to a level mismatch between searcher filtering and nested-level execution.

Changes:

• Introduced a Global() flag in the FieldSet interface to identify field-agnostic queries
• Removed searcher-level nested document filtering from MatchAllSearcher
• Updated nested collector activation logic to trigger for global queries, ensuring consistent filtering at the collector level

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
search/util.go	Converted FieldSet from a map type to an interface with a private implementation, adding Global() flag to track field-agnostic queries
search/query/query.go	Updated ExtractFields to set the Global() flag for MatchAllQuery and DocIDQuery
search/searcher/search_match_all.go	Removed nested document filtering logic (isNested method) to unify filtering at collector level
index_impl.go	Enhanced nested collector activation logic to include global queries; refactored field iteration to use VisitFields
registry/nested.go	Adapted to new FieldSet interface using VisitFields method
index_alias_impl.go	Updated field iteration to use new FieldSet.VisitFields API
mapping/index.go	Updated method call from Slice() to Fields()
search_nested_test.go	Added comprehensive test cases for match_all, docID, and Boolean filter queries in nested mode
search/query/query_test.go	Extended test coverage for field extraction with expGlobal assertions

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[coveralls]

coverage: 52.657% (+0.04%) from 52.621%
when pulling 4d4984d on bugFix
into ca7d4ab on master.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

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[Copilot]

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[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

registry/nested.go:1

• Potential panic when accessing ancestors[len(ancestors)-pos-1] if ancestors is empty or if pos >= len(ancestors). With the changes allowing global queries in nested contexts, this function may be called with empty ancestor chains from top-level documents matched by match_all queries. Add bounds checking to prevent panics.

//  Copyright (c) 2026 Couchbase, Inc.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.

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