CLI: set localhost as default for database hostname in verdi setup

[sphuber]

Fixes #4907

The default was actually being defined on the option, however, it was
taken from the pgsu.DEFAULT_DSN dictionary, which defines the database
hostname to be None. Still, 9 out of 10 times the database is on the
localhost so not having this as a default is kind of annoying and
unnecessary.

[ltalirz]

thanks @sphuber - to my knowledge, there actually is a difference between None and localhost, see
https://github.com/aiidateam/pgsu/blob/43d8d305053e9f6a1352295bf9a3f6955881d5ba/pgsu/__init__.py#L17

In particular, I believe that localhost will not work with the default postgres setup on ubuntu that goes via the local connection.

What is annoying about the default?

[codecov]

Codecov Report

Merging #4908 (8ea1c8c) into develop (87ab7e3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #4908   +/-   ##
========================================
  Coverage    80.07%   80.07%           
========================================
  Files          518      518           
  Lines        36683    36683           
========================================
  Hits         29371    29371           
  Misses        7312     7312           

Flag	Coverage Δ
django	74.56% <ø> (+0.03%)	⬆️
sqlalchemy	73.50% <ø> (ø)

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Impacted Files	Coverage Δ
aiida/cmdline/params/options/__init__.py	98.27% <ø> (ø)
aiida/cmdline/params/options/commands/setup.py	56.85% <ø> (ø)

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[sphuber]

In particular, I believe that localhost will not work with the default postgres setup on ubuntu that goes via the local connection.

Maybe circumstantial evidence but I have been using localhost on Ubuntu 18.04 and 20.04 since forever without any issues.

What is annoying about the default?

I always have to specify localhost when creating a new profile. Since most cases would actually use this, it seems to me like there is not really a reason to not have that as a default.

[ltalirz]

In particular, I believe that localhost will not work with the default postgres setup on ubuntu that goes via the local connection.

Maybe circumstantial evidence but I have been using localhost on Ubuntu 18.04 and 20.04 since forever without any issues.

I might be wrong (I'll check). Can you please share the uncommented lines of your /etc/postgresql/10/main/pg_hba.conf ?

[ltalirz]

On second thought, I think you are right.

'localhost' is the correct default there, while None is a good thing to try for pgsu (because it is the only way you can access the psql shell without a password).

You may want to include this information in the commit message.

[sphuber]

local   all             postgres                                peer

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     peer
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
local   replication     all                                     peer
host    replication     all             127.0.0.1/32            md5
host    replication     all             ::1/128                 md5

This is the default config of postgres-12 on Ubuntu 20.04

[sphuber]

You may want to include this information in the commit message.

Cheers, will do.