“Style” lint from Pylint and lint configuration

[mcarton]

Pylint has a few interesting “bad style” lints, eg.:

% cat a.py
def test(a, b, c, d, e, f):
    foo = a+b
    return foo
% pylint a.py
No config file found, using default configuration
[…]
C:  1, 0: Invalid argument name "a" (invalid-name)
[…]
C:  1, 0: Invalid argument name "f" (invalid-name)
[…]
R:  1, 0: Too many arguments (6/5) (too-many-arguments)
C:  2, 4: Black listed name "foo" (blacklisted-name)
[…]

The three of those are interesting I think.

• invalid-name forbids one-lettered names for parameters or variables (but whitelists i, j, and k, to which I think we should add n; see also Lint non-expressive variable names #644, which suggests linting one-lettered variables if there are more than 3 in the same scope);
• too-many-arguments lints for “complex” functions with too many parameters, here the default threshold for “too many” is >5;
• blacklisted-name lints for anything named foo, bar, baz, toto, tutu, or tata (some pylint dev must be French), which you might write “temporarily” eg. for debugging and forget to rename/remove.

The thing is pylint lints are all configurable through command line arguments or in a config file. I think we should have such configuration if we want to implement those lints. The cyclomatic-complexity and probably other lints will also benefit from it.

I suggest a Clippy.toml file, which could contain something like

too-many-arguments-threshold = 7
blacklisted-names = ["toto", "tutu", "tata", "titi"]
cyclomatic-complexity-threshold = 42

maybe in a [configuration] table or something and to allow to use:

#![plugin(clippy(too_many_arguments_threshold="7"))]

What do you think?

[Manishearth]

I like the idea. The default too_many_arguments_threshold probably should be larger for us? It's not always easy to struct-ify things and python has named arguments amongst other things to make these things easier to manage

[mcarton]

That’s what I though too, if we’re going to implement that lint, we should look at real projects to see what unreasonable functions look like.

[killercup]

I like this! There are a lot of places where clippy can be allowed to make opinionated like these, though, so it might be a good idea to split these things into a separate lint group (or even crate).

The configuration file is a good idea as well. Would it be possible to enable lints/set lint levels there as well? (I can imagine this being difficult).

[ticki]

I don't like the lint for one letter variables, since (as long as they're not overused or abused) can be a handy tool for temporary variables. I like the idea of restricting the number of single letter variables in the same scope.