explain_get_index_name() applied quote_identifier() to the index name. This is fine for text output, but the non-text output formats all have their own quoting conventions and would much rather start from the actual index name. For example in JSON you'd get something like
"Index Name": "\"My Index\"",
which is surely not desirable, especially when the same does not happen for table names. Hence, move the responsibility for applying quoting out to the callers, where it can go into already-existing special code paths for text format.
This changes the API spec for users of explain_get_index_name_hook: before, they were supposed to apply quote_identifier() if necessary, now they should not. Research suggests that the only publicly available user of the hook is hypopg, and it actually forgot to apply quoting anyway, so it's fine. (In any case, there's no behavioral change for the output of a hook as seen in non-text EXPLAIN formats, so this won't break any case that programs should be relying on.)
Digging in the commit logs, it appears that quoting was included in explain_get_index_name's duties when commit 604ffd280 invented it; and that was fine at the time because we only had text output format. This should have been rethought when non-text formats were invented, but it wasn't.
This is a fairly clear bug for users of non-text EXPLAIN formats, so back-patch to all supported branches.
Per bug #16502 from Maciek Sakrejda. Patch by me (based on investigation by Euler Taveira); thanks to Julien Rouhaud for review.
63d2ac23b0 Undo double-quoting of index names in non-text EXPLAIN output formats.
src/backend/commands/explain.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)