cli: support \d client-side command with no arguments

[rafiss]

\d can be used with no arguments as a way to show all the
tables in a database. This is an alias for \dt.

Release note (cli change): Support \d client-side command with no
arguments as an alias for \dt, for more ease of adoption by psql
users.

[cockroach-teamcity]

This change is 

[jordanlewis]

LGTM

[kenliu]

looks great, nice addition!

Reviewed 2 of 2 files at r1.
Reviewable status: complete! 0 of 0 LGTMs obtained

[knz]

No comment on the code but I'll paste this comment I made to Ken a while ago: the word "metacommand" is an anachronism and would be best replaced by "client-side command".

Small bit of history: the word "metacommand" was introduced by pg in the 1980s-1990s at a time where there was a lot of activity in PL design. Back then there was a craze around "meta" constructs: bits of syntax in a language that would be expanded into other bits of syntax in the same language before the program would be further compiled/interpreted. Back then they were calling it "meta syntax" or "meta languages".

1. We call this "preprocessing" and "macros" today, not "meta"

2. CockroachDB does not do preprocessing on these things server-side. They are in fact compiled by the client into other things sent to the server.

Hence the name "client-side command". Also the word "client-side" puts the emphasis on the fact this is specific to the CockroachDB SQL shell, and therefore users should not expect \d etc to work if using another SQL client. With a true "meta-command" the meta-command would be understood server-side and the client would not matter.

[rafiss]

Thanks for the feedback everyone. @knz: that makes sense, thanks for the background! I was copying the verbiage used in the initial PR that added support for this, but I will adjust the wording in the code and commit message before merging.

[rafiss]

bors r+

[craig]

Build succeeded

• GitHub CI (Cockroach)