Summary

Fixes #3686

• Adds support for indexing more than 32 columns using composite types with ROW(...)::type expressions
• Composite fields are searchable individually by their field names from the type definition

Changes

Core Module (pg_search/src/postgres/composite.rs)

• CompositeSlotValues - Unpacks composite values upfront during construction for field extraction
• CompositeFieldInfo - Metadata struct for composite type fields
• CompositeError - Validation errors for nested composites, anonymous ROW, and domain types
• Helper functions: is_composite_type, get_composite_type_fields, get_composite_fields_for_index

Field Matching (pg_search/src/api/operator.rs)

• expr_matches_node - New helper function for matching WHERE clause expressions against indexed expressions
• Extended field_name_from_node to detect composite type fields and match them by field name

Integration (pg_search/src/postgres/utils.rs)

• FieldSource::CompositeField variant for composite-derived fields
• get_field_value helper to extract individual fields from unpacked composites
• Extended extract_field_attributes to detect and expand composite expressions
• Duplicate field name detection across composites and regular columns

Parallel Build & Insert

• build_parallel.rs and insert.rs updated to use CompositeSlotValues
• mvcc.rs updated for MVCC-aware composite unpacking

Usage Example

-- Create a composite type with the fields you want to index
CREATE TYPE product_search AS (name TEXT, description TEXT, category TEXT);

-- Create table with regular columns
CREATE TABLE products (
    id SERIAL PRIMARY KEY,
    name TEXT,
    description TEXT,
    category TEXT
);

-- Create BM25 index using composite type
CREATE INDEX idx_products ON products USING bm25 (
    id,
    (ROW(name, description, category)::product_search)
) WITH (key_field = 'id');

-- Search by individual field names from the composite type
SELECT * FROM products WHERE name @@@ 'Widget';
SELECT * FROM products WHERE description @@@ 'amazing';

-- Or with pdb functions for more control
SELECT * FROM products WHERE name @@@ pdb.term('Widget');
SELECT * FROM products WHERE name @@@ pdb.fuzzy_term('Widgt', distance => 1);

Test plan

• 47 pg_regress test sections covering:
  • composite.sql (39 test sections): Basic indexing, >32 fields, 100 fields, JSON/array fields, tokenizers, error cases, parallel builds, MVCC, and more
  • composite_advanced.sql (8 test sections): Field-level queries with field @@@ query syntax, pdb functions, scoring, snippets
• cargo fmt and cargo clippy clean