User comments in config file lost after writing to config via `pgcli`

Description

First of all, thanks for a great tool, I use it a lot.

User comments to the pgcli config file are getting lost after the config file gets modified via pgcli itself (e.g. adding a named query). According to https://github.com/dbcli/pgcli/issues/1162#issuecomment-740076796 they should remain. Additionally, all whitelines from at least the [named queries] section onward get lost as well.

I can reproduce this on a clean virtualenv and with a fresh config file.

Reproduce

Log from my reproduction attempts:

• Removed previous config file
• Created new temp virtualenv (using the system Python 3.6.9), installed new pgcli (pip install pgcli)
• Started pgcli, this created a new config file
• Config file (from [named queries] section onward; same goes for the config file snippets below) at this point:

  # Named queries are queries you can execute by name.
  [named queries]
  
  # DSN to call by -D option
  [alias_dsn]
  # example_dsn = postgresql://[user[:password]@][netloc][:port][/dbname]
  
  # Format for number representation
  # for decimal "d" - 12345678, ",d" - 12,345,678
  # for float "g" - 123456.78, ",g" - 123,456.78
  [data_formats]
  decimal = ""
  float = ""
  

• Save new named query from pgcli: \ns foo bar. Config file snippet after this:

  [named queries]
  foo = bar
  [alias_dsn]
  [data_formats]
  decimal = ""
  float = ""
  

  • NOTE: the “# Named queries are queries you can execute by name.” comment (and the preceding whiteline) above the [named query] section header is now gone as well (while the “# style classes for colored table output” comment above output.header = "#00ff5f bold" remained in tact. As did all other comment and whitelines earlier in the file)
• Close pgcli (just in case), add user comment above the foo = bar named query entry. Config file snippet after this:

  [named queries]
  # My comment
  foo = bar
  [alias_dsn]
  [data_formats]
  decimal = ""
  float = ""
  

• Start pgcli again, add new named query: \ns bar SELECT 1. Config file snippet after this:

  [named queries]
  foo = bar
  bar = SELECT 1
  [alias_dsn]
  [data_formats]
  decimal = ""
  float = ""
  

• Close pgcli (just in case), add record and comment to [alias_dsn]. Config file snippet after this:

  [named queries]
  foo = bar
  bar = SELECT 1
  [alias_dsn]
  # I feel like I'm getting lost
  baz = postgresql://foo@localhost/postgres
  [data_formats]
  decimal = ""
  float = ""
  

• Start pgcli again, add new named query: \ns baz SELECT 2. Config file snippet after this:

  [named queries]
  foo = bar
  bar = SELECT 1
  baz = SELECT 2
  [alias_dsn]
  baz = postgresql://foo@localhost/postgres
  [data_formats]
  decimal = ""
  float = ""
  

Did another quick test (only some of the steps from above) with a Python 3.9.0 (via pyenv) temp virtualenv, same results. Tried this one with both a pip install pgcli and a pip install git+https://github.com/dbcli/pgcli@master.

The same happens in my proper config file using my proper pgcli install, which contains many more named queries and DSN aliases.

Environment, verison info

• OS: Ubuntu 18.04.5 (x64)

• pgcli:

  • In most of the tests above:

    Server: PostgreSQL 9.6.13
    Version: 3.1.0
    

  • My proper install:

    Version: 3.0.0
    

• pip freeze of my proper install:

``` cffi==1.14.0shared libraries cli-helpers==1.2.1 click==7.1.1 configobj==5.0.6 cryptography==2.9.2 dbus-python==1.2.16 humanize==2.3.0 importlib-metadata==1.7.0 jeepney==0.4.3 keyring==21.2.1 pgcli==3.0.0 pgspecial==1.11.9 pkg-resources==0.0.0 prompt-toolkit==3.0.8 psycopg2==2.8.5 pycparser==2.20 Pygments==2.6.1 SecretStorage==3.1.2 setproctitle==1.1.10 six==1.14.0 sqlparse==0.3.1 tabulate==0.8.7 terminaltables==3.1.0 wcwidth==0.1.9 zipp==3.1.0 ```

[j-bennet]

I submitted a PR into ConfigObj repo. We’ll see what happens with that.

https://github.com/DiffSK/configobj/pull/212

[j-bennet]

Fixed via https://github.com/dbcli/pgcli/pull/1251.

This is by no means a perfect solution. I wish that configparser in stdlib supported comments on write, unfortunately it does not. I’d like to try and submit a PR to https://github.com/DiffSK/configobj to fix this issue, but it will not happen immediately.