[Fix #3937] Add new Rails/StartEndWith cop

[tdeo]

This cop checks for consistent use of starts_with? and ends_with? string
methods or consistent use of start_with? and end_with?

No option to mix consistent use of starts_with? and end_with? or the opposite.

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Used the same coding conventions as the rest of the project.
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• All tests are passing.
• The new code doesn't generate RuboCop offenses.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[bbatsov]

We should actually have a single cop checking for all similar ActiveSupport aliases.

[tdeo]

Do you have any specific one in mind? Or how could we enumerate all such singular / plural forms in aliases?

[bbatsov]

Here's a listing of all the methods - http://guides.rubyonrails.org/active_support_core_extensions.html

[tdeo]

There's indeed several other examples: String#camelize and String#titleizealiased respectively to String#camelcase and String#titlecase.

Otherwise there's also:

• Array#append and Array#prepend
• Hash#reverse_update, Hash#to_options and Hash#to_options!
• Several Date and DateTime methods.
• The Numeric#byte, Numeric#kilobyte, Numeric#megabyte, ... available in singular and plural forms (which I fell should belong in Rails/PluralizationGrammar)

I'm not sure if all of them should belong to the same cop (which would then be Rails/ActiveSupportAliases that can be enabled / disabled) ?

[rrosenblum]

Aren't some of these aliases designed for grammatical purposes more so than as a replacement? In my mind this should work similar to what is being done in Rails/PluralizationGrammar. Rather than enforcing an always use one style, I would expect this to attempt to figure out if the receiver uses a singular or a plural name.

[bbatsov]

Aren't some of these aliases designed for grammatical purposes more so than as a replacement?

They were, but this is pointless in a programming language. Matz himself mentioned this a while back when asked what he thinks about those.

[tdeo]

So we would rather head towards a cop Rails/VanillaSemantics that would handle all of them at once?

People will still have a choice to enable or disable it anyway. But yeah, it would be "all or nothing".

[tdeo]

@bbatsov I renamed the cop to Rails/ActiveSupportAliases to be consistent with #3935.

I'm only checking for String#starts_with?, String#ends_with?, Array#append and Array#prepend which are the only aliases to core ruby methods (the other I mentioned before are actually alias to other ActiveSupport methods).

A detail here: I'm not supporting autocorrect from Array#append to Array#<< because I didn't know how to handle removing the . for method call and the parameter parenthesis if present. I felt that autocorrecting to array.<<(element) was too ugly.

[bbatsov]

You have a typo here - # should be *.

[bbatsov]

This sentence should end with a ..

[bbatsov]

Add . here.

[bbatsov]

Add a blank line between the code examples.

[bbatsov]

A detail here: I'm not supporting autocorrect from Array#append to Array#<< because I didn't know how to handle removing the . for method call and the parameter parenthesis if present. I felt that autocorrecting to array.<<(element) was too ugly.

You can simply replace . with op in the autocorrect. It's accessible via node.loc as everything else.

I've added a few small remarks to the code. Btw, ideally this cop should be configurable to both enforce consistent non-usage of the aliases and their consistent usage. I'll merge the cop even in its current form, but I guess some people won't be happy about the lack of config options.

[tdeo]

I still can't figure a good way for autocorrecting append that handles all those cases:

array.append(3)
array.append 3
array
  .append 3

[bbatsov]

Well, let's leave this out of the cop's scope for now.

[tdeo]

And about different styles, I don't see any issue adding the option for consistent non-usage, but I think some people will still be unhappy having to write Array#append just because you want to use String#ends_with?.

[bbatsov]

Fine by me. Just squash and rebase and I'll merge this.