Re: PSQL schema "describe" \dn is not escaping quotes

Hi Peter,

Thanks for v7. It applies cleanly on master, builds without warnings, and
make check passes.
The quoting fix itself looks right: both queries now take the actual schema
name via appendStringLiteralConn(). I tried names with embedded ', ", \
and ., plus mixed case. They all display correctly with the right
publications footer, and \dn "e_sch1" now shows the footer that master
silently left out.

I have a couple of comments:
1. Backpatching. Nishant showed the bug goes back to PG15, but v7 also
changes what \dn prints whenever a pattern is given:
- each match is now its own "Schema "x"" table instead of one "List of
schemas"
- the "(N rows)" footer is gone
- in non-quiet mode, a pattern with no match is now an error

I don't think changes to user-visible output can go into 15–18. Could this
be split into two patches? 0001 would be a minimal escaping fix that can be
backpatched, e.g. keying the footer off PQgetvalue(res, 0, 0) when exactly
one row comes back. 0002 would be the per-schema display, master only, and
would probably need its own discussion. psql-ref.sgml also still says
matching schemas "are listed", so 0002 would need a doc update.

2. The no-match behaviour doesn't actually match \dt. The comment says "to
be same as \dt", but listTables() prints the error and then returns true,
while listSchemas() jumps to error_return and returns false. So under
ON_ERROR_STOP, \dn nosuch now aborts a script where it used to print an
empty table:

$ psql -v ON_ERROR_STOP=1 -c '\dn e_nosuch' -c 'select 1'; echo "exit=$?"
Did not find any schemas named "e_nosuch".
exit=1
$ psql -v ON_ERROR_STOP=1 -c '\dt e_nosuch' -c 'select 1'; echo "exit=$?"
Did not find any tables named "e_nosuch".
?column?
----------
1
(1 row)

exit=0

Also:
- the no-pattern message "Did not find any schemas" has no trailing
period, unlike the other messages in describe.c
- in quiet mode a no-match still prints the old empty "List of
schemas" table, so there are two output styles depending on -q
- pg_regress runs psql with -q, so none of the new error paths are
exercised by the regression tests

3. \dn * now prints a separate table for every schema in the database,
pg_catalog, pg_toast and information_schema included. With CSV output, a
multi-match pattern now produces several header rows in a row, which would
break anything that parses the output:
\pset format csv
\dn e_sch*
Name,Owner
e_sch1,surya
Name,Owner
e_sch2,surya
Name,Owner
e_sch3,surya
This is one more reason to keep the redesign out of the bug fix, or at
least call it out explicitly.

4. Minor issues in describeOneSchemaDetails():
- The footer query has no separator after the literal. With
ECHO_HIDDEN it shows up as WHERE n.nspname = 'e_sch1'ORDER BY 1;. It works,
but a "\n" before ORDER BY would fix it.
- The footer query still uses appendPQExpBuffer() with no format
arguments. Jim pointed this out for v1, but v2 only changed the ORDER BY
line. appendPQExpBufferStr() would do.
- myopt.topt.default_footer = false is only set inside the sversion >=
150000 branch, so against an older server each schema table still ends with
"(1 row)".

5. Tests:
- CREATE PUBLICATION pub_sch_1 FOR TABLES IN SCHEMA SCH_1 is unquoted,
so it publishes sch_1, not "SCH_1". The expected output is correct, but a
reader will probably assume the opposite. Could you add a comment, or use
distinct names?
- There's no coverage for \dn+ with a pattern or for names containing
a backslash.

Regards,
Surya Poondla