More cops(rules)

[bbatsov]

Hey guys,

Here's a list of the more important rules that we should implement in the future.

• Use Kernel#loop with break rather than begin/end/until or begin/end/while for post-loop tests.
• Avoid return where not required for flow of control.
• Avoid self where not required. (It is only required when calling a self write accessor.)
• Avoid line continuation (\) where not required. In practice, avoid using line continuations at all~~.
• Use only ascii symbols in identifiers and comments
• When using reduce with short blocks, name the arguments |a, e| (accumulator, element).
• When defining binary operators, name the argument other. (like def +(other))
• Comment annotation would be all upcase and at the beginning of the comment like (# TODO improve performance).
• Favor the use of module_function over extend self when you want to turn a module's instance methods into class methods.
• Use the attr family of functions to define trivial accessors or mutators.
• Use def self.method to define singleton methods. This makes the code easier to refactor since the class name is not repeated.
• Signal exceptions using the fail method. Use raise only when catching an exception and re-raising it (because here you're not failing, but explicitly and purposefully raising an exception).
• Never return from an ensure block. If you explicitly return from a method inside an ensure block, the return will take precedence over any exception being raised, and the method will return as if no exception had been raised at all. In effect, the exception will be silently thrown away.
• Use implicit begin blocks where possible.
• Don't suppress exceptions.
• Avoid rescuing the Exception class. This will trap signals and calls to exit, requiring you to kill -9 the process.
• Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is).
• Prefer %w to the literal array syntax when you need an array of strings.
• Use %r only for regular expressions matching more than one '/' character.
• Favor %r if you have more than 1 '/' characters in your regexp.
• Avoid %q, %Q, %x, %s, and %W.
• Prefer () as delimiters for all % literals.
• Avoid methods longer than 10 LOC (lines of code). Ideally, most methods will be shorter than 5 LOC. Empty lines do not contribute to the relevant LOC. (this cop should have configurable max length)
• Avoid alias when alias_method will do.
• Avoid more than three levels of block nesting.
• One space after if, unless, etc.
• Use two spaces for indentation.
• Add empty lines around private and protected.
• Indent private and protected as much as method definitions.

Details and examples about most rules are available in the guide itself.

I'm opening this ticket mostly so we can discuss who would like to implement what, so that we don't end up with two people working on the same cop. When somebody(me included) starts to work on a cop he'd write a comment here; when he's done - we'd scratch the rule from the list.

So, who'd like to pick a task first? :-)

@jonas054, @vsakarov, @emou

[jonas054]

I want to do "Use only ascii symbols in identifiers and comments". The list is a great idea, by the way.

[bbatsov]

It's yours then.

[jdanielnd]

I've written a cop for "Prefer %w to the literal array syntax when you need an array of strings." and now it detects that style rule on various code files from the project. Should I correct them to match this new rule too?

[bolandrm]

This can be crossed off the list:

• Avoid methods longer than 10 LOC (lines of code). Ideally, most methods will be shorter than 5 LOC. Empty lines do not contribute to the relevant LOC. (this cop should have configurable max length)

I'm going to work on "When using reduce with short blocks, name the arguments |a, e|"

[bbatsov]

I guess I crossed it off just as you were typing this comment. :-)

Great, looking forward to it.

[jonas054]

I'll do "Use %r only for regular expressions matching more than one '/' character".

[emou]

I'll look into "Avoid more than three levels of block nesting."

[bbatsov]

Great, @emou. I'd suggest to actually use a customizable param for that particular check(instead of hardcoding 3), since a lot of people might disagree with the number prescribed by default.

[bbatsov]

I'll do 'Favor %r if you have more than 1 '/' characters in your regexp'.

[jurriaan]

What do you think about an indentation Cop?

ps. Could you use a task list? I think that's more clear.

[bbatsov]

Yep, that would be a great addition. The ruby interpreter detect misaligned ends, but nothing more than that. An indentation cop would be an awesome addition. Do you volunteer to write it? :-)

ps. Will do!

[bbatsov]

Done.

[bbatsov]

@jonas054 @yujinakayama I think we should try to wrap this issue before 1.0. I'd suggest we continue the old practice of doing a cop at time until we're out of cops. I'll start with the unneeded return check.

[jonas054]

I'll do Avoid self where not required.

[bbatsov]

I'll do the implicit begin next.

[jonas054]

I'll do "Comment annotation should be all upper case and at the beginning of the comment".

[jonas054]

I'll do "Prefer modules to classes with only class methods" next.