Regression in 1a28dc3887.
The usage of CONCAT to allow SearchVector to deal with non-text fields
made the generated expression non-IMMUTABLE which prevents a functional
index to be created for it.
Using a combination of COALESCE and ::text makes sure the expression
preserves its immutability.
Refs #29582. Thanks Andrew Brown for the report, Nick Pope for the
review.
Adds a reasonably feature complete implementation of full text search
using the built in PostgreSQL engine. It uses public APIs from
Expression and Lookup.
With thanks to Tim Graham, Simon Charettes, Josh Smeaton, Mikey Ariel
and many others for their advice and review. Particular thanks also go
to the supporters of the contrib.postgres kickstarter.