Try to implement more M:F/A ignore rules

[onno-vos-dev]

In order to avoid marking an entire module to be ignored, I would like to explore the option of being able to ignore specific functions within a module, possibly including the arity as an optional value. The only rule that currently supports this behaviour is max_function_length_config and it would be great to support more rules in this way.

Especially on larger modules (one can argue that they shouldn't exist but reality sometimes punches us in the face), being forced to ignore the entire module because of one function that violates a specific rule makes me all sad.

Before exploring if this is feasible, I'd like to ask:

1. Has this been considered and dropped due to feasibility reasons?
2. Is this a feature that you would like to see implemented?

[elbrujohalcon]

I ❤️ this idea and I would totally implement it with module attributes, just like dialyzer and xref (within rebar3 or xref_runner) do.
In other words, I would allow for individual modules to have some way to override the global config with attributes like:

-module my_module.

-elvis #{ module => [{elvis_style, god_modules, disable}]
        , {my_function, 2} => [{elvis_style, operator_spaces, #{rules => [{right, ","}]}}]
        , …
        }.

-export [my_function/2].

my_function(A, B) -> …

That would be amazing!

[onno-vos-dev]

I really like your second suggestion but that's a completely different beast altogether.

I can start looking into implementing my proposal. I suggest breaking off your 2nd approach to a different issue and we can track that seperately? 👍

[elbrujohalcon]

Well… I'm not entirely sure what's your proposal, then.
Just add ignore clauses to several existing rules?
If that's so, then by all means go ahead!

[onno-vos-dev]

Example config of what I mean

% -*- mode: erlang -*-
[{elvis,
  [{config,
    [ #{dirs => [ "lib/my_awesome_app/src"
                , "lib/my_legacy_app/src"
                ],
        filter => "*.erl",
        ruleset => erl_files,
        rules => [ {elvis_style, nesting_level,
                    #{ level => 3,
                       ignore_functions => [ {legacy_module, foo}
                                           , {legacy_module, bar, 2}
                                           ]
                     }}
                 ]}
    ]
   }
  ]
 }
].

Currently the nesting_level rule only allows ignoring a module. I'd like to be able to ignore legacy_module but only the function foo with any arity and bar with arity 2. In essence I want to bring the ignore_functions that is available functionality for the max_function_length_config-rule to more rules and allow a much more granular ignoring behavior than what is currently possible.

The problem that I'm trying to solve is implementing Elvis on a large codebase where Elvis is unhappy about a handful of functions within modules and want to avoid having to mark the entire module as a ignore. I want to start by adding these functions as ignore_functions and having the rest of the module be checked. This way, no more style issues can sneak into the code base and combined with https://github.com/inaka/elvis/issues/487 slowly but surely remove the style issues and get Elvis to dance happily-ever-after.

Does that clarify this?

[elbrujohalcon]

It does clarify and yes… by all means, go ahead!!

[paulo-ferraz-oliveira]

I vote that we slightly change ignore to encompass ignore_functions and then add that to all the rules.

ignore could be :: module() | {module(), function()} | {module() | function() | arity()}

@elbrujohalcon: at the same time, it seems this Issue might have been closed by a previous PR already. I'll later check if a new Issue should be created with my "proposal" (I'm imagining this isn't a new suggestion, in any case).

[elbrujohalcon]

@paulo-ferraz-oliveira I like your idea.
Besides… I still like the -elvis attribute 😎

[paulo-ferraz-oliveira]

Also partially mentioned in #507.