[Avocado-devel] RFC: Configuration by convention

[Beraldo Leal]

On Tue, Dec 03, 2019 at 07:28:10AM +0100, Lukáš Doktor wrote:
> >> The default comes from /etc. You can checkout the `avocado/plugins/run.py` for details:
> >>
> >>         sysinfo_default = settings.get_value('sysinfo.collect',
> >>                                              'enabled',
> >>                                              key_type='bool',
> >>                                              default=True)
> >>         sysinfo_default = 'on' if sysinfo_default is True else 'off'
> >>         parser.add_argument('--sysinfo', choices=('on', 'off'),
> >>                             default=sysinfo_default, help="Enable or disable "
> >>                             "system information (hardware details, profilers, "
> >>                             "etc.). Current:  %(default)s")
> >>
> >> 1. `--sysinfo on` => force-enable
> >> 2. `--sysinfo off` => force-disable
> >> 3. no `--sysinfo` => use the value from /etc
> > 
> > IIUC, the default comes from the source code:
> > 
> >   settings.get_value(..., default=True)
> > 
> > If the option is missing on config file and there is no --sysinfo option
> > on command line, the default will be "True", right?
> > 
> > So, there are 3 ways to use, but the possible values are "on" or "off",
> > right? Fix-me if I'm wrong, but what is the third option other than,
> > "on" and "off"? The key_type is still a bool, right?
> > 
> 
> 1 -> will be always enabled
> 2 -> will be always disabled
> 3 -> depends on /etc configuration. If not present there it uses True
> 
> So the (3) means it reflects the configuration option. If we make it
> only a bool (present/missing) there would be no way to force-override
> the /etc configuration.

Sorry if I'm insisting on this, but I just would like to make sure that
I'm not missing anything.

Regarding the "tri-state" ...

My question is: What happens, in terms of behavior, if `sysinfo = none`?
Is there behavior for "none"? You are showing me that the "third state"
is "none", but what happens if it is "none"?

Some logic that could help you understanding my findings and thought:

    1. Configuration file parse is already a bool:
       * settings.get_value has key_type = bool;
       * settings.get_value has default = True;
       * settings.get_value has an "allow_blank" set to False;
       * At the end of this parsing, the line above will transform
       anything into "on" or "off":

	sysinfo_default = 'on' if sysinfo_default is True else 'off'

    2. Argument Parse is not an explicit bool, but it is limited to
    "on/off" with default to "on" or "off". 
      * At the end of this parsing, we have "on" or "off".

So, IIUC, in terms of behavior, we have only: disabled or enabled. At
the end of all parsing stuff, it will reflect only on enabled or
disabled. I could not find any code execution (behavior) based on
"none". Please, show me what happens when sysinfo = none.

Regarding the "force-override the /etc configuration" ...

IMO, we could improve the code here, with some basic and common logic,
and keeping the "force-override" in /etc/:

    1. Source code knows the default values, let's say the "config object"
    into memory;

    2. Parse configuration file options into the "config object",
    overwriting the defaults;

    3. Parse the command line arguments into the "config object",
    overwriting the configuration file;

    4. Let the "config object" (already parsed) available to all code.

I understand that we don't have a 1:1 mapping between config file
options and argument options, and item 3 is limited. But the current
state already like that, right?

Again, sorry for the insistence, let me know if I'm missing something.

Regards,
Beraldo