Deprecate Unicode#downcase/upcase/swapcase.

[frodsan]

• Deprecates ActiveSupport::Multibyte::Unicode#downcase/upcase/swapcase in favor of using String methods directly.
• Removes ActiveSupport::Multibyte::Chars wrappers around the following String methods: #downcase, #upcase, #swapcase, and #capitalize.

[rails-bot]

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @sgrif (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

This repository is being automatically checked for code quality issues using Code Climate. You can see results for this analysis in the PR status below. Newly introduced issues should be fixed before a Pull Request is considered ready to review.

Please see the contribution instructions for more information.

[jeremy]

Related to #26743 and #26403.

When you already have a Chars object, this deprecation message tells you to use a method from a different class. How will a user understand this and what should they do?

Is the underlying intent to deprecate ActiveSupport::Multibyte::Chars itself?

[frodsan]

The intent is to deprecate the wrappers for the String methods (upcase, downcase, swapcase) in AS::Multibyte::Unicode. These methods are used in AS::Multibyte::Chars so I changed those to just use the String methods directly. The warning only appears if you use the Unicode methods directly. I added a test case to show this behavior, but here is the output in irb:

>> ActiveSupport::Multibyte::Unicode.downcase("DEPRECATED")
DEPRECATION WARNING: ActiveSupport::Multibyte::Unicode#downcase is deprecated and will be removed from Rails 6.1. Use String#downcase instead. (called from block (3 levels) in run at /Users/frodsan/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/minitest-5.11.3/lib/minitest/test.rb:98)
deprecated
>> "NOTDEPRECATED".mb_chars.downcase.to_s
notdeprecated

I think these could be the wrapper methods referred here: #26743 (comment)

[jeremy]

That sounds good. Let's deprecate these methods together as a group and change the warning message to suggest using String directly since the ActiveSupport::Multibyte::Unicode wrapper is no longer needed.

[jeremy]

/cc @mtsmfm @amatsuda

[amatsuda]

+1 from me!

[mtsmfm]

👍

[frodsan]

@jeremy I made the changes. I hope I got it right :) ... I also removed the method definitions from Multibyte::Chars because that logic is already being handled by #method_missing.

[frodsan]

I'm also removing the wrapper around String#capitalize after discussing this with @mtsmfm (#26743 (comment))

[mtsmfm]

reverse can be chars(@wrapped_string.scan(/\X/).reverse.join)

[jeremy]

Thank you @frodsan. For those interested, let's look at deprecating Unicode.normalize and changing Chars#reverse implementation in new PRs.

[jeremy]

Looks like a failing test remains:

MultibyteCharsUTF8BehaviourTest#test_method_works_for_proxyed_methods:
FrozenError: can't modify frozen String
    /home/travis/build/rails/rails/activesupport/lib/active_support/multibyte/chars.rb:61:in `capitalize!'
    /home/travis/build/rails/rails/activesupport/lib/active_support/multibyte/chars.rb:61:in `method_missing'
    /home/travis/build/rails/rails/activesupport/test/multibyte_chars_test.rb:481:in `call'
    /home/travis/build/rails/rails/activesupport/test/multibyte_chars_test.rb:481:in `test_method_works_for_proxyed_methods'

[frodsan]

@jeremy I fixed the failing test.

I just found that the bang version of these methods will raise FrozenError when the wrapped string is frozen. I think that should be expected:

>> (-"hello").mb_chars.chomp!
FrozenError (can't modify frozen String)
>> (-"hello").mb_chars.gsub!("m", "")
FrozenError (can't modify frozen String)
>> (-"hello").mb_chars.downcase!
FrozenError (can't modify frozen String)

I'll work on the Unicode#normalize deprecation.