[Fix #6917] Bump Bundler dependency to >= 1.15.0

[koic]

Fixes #6917.

This PR bumps Bundler dependency to >= 1.15.0.

Bundler 2 has already been released.
This PR drops old Bundler versions (1.14 or lower) to prevent the following error.

Bundler 1.14

An unexpected error occurs.

% bundle _1.14.6_ exec rubocop
bundler: failed to load command:
rubocop (/Users/koic/.rbenv/versions/2.6.2/lib/ruby/gems/2.6.0/bin/rubocop)
TypeError: no implicit conversion of String into Integer
  /Users/koic/.rbenv/versions/2.6.2/lib/ruby/gems/2.6.0/gems/rubocop-0.67.1/exe/rubocop:16:in
  `<top (required)>'
  /Users/koic/.rbenv/versions/2.6.2/lib/ruby/gems/2.6.0/bin/rubocop:23:in
  `load'
  /Users/koic/.rbenv/versions/2.6.2/lib/ruby/gems/2.6.0/bin/rubocop:23:in
  `<top (required)>'

Bundler 1.15

Errors does not occur as expected.

% bundle _1.15.0_ exec rubocop
[Warn] Performance Cops will be removed from RuboCop 0.68. Use
rubocop-performance gem instead.
       https://github.com/rubocop-hq/rubocop/tree/master/manual/migrate_performance_cops.md

(snip)

---

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).
• 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.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[bbatsov]

Thanks!

[deivid-rodriguez]

Hi @koic! I don't think this PR fixes the issue.

bundler is not a runtime dependency of rubocop, so changing the development_dependency won't have any effect for end users.

What you can do is activate the version your code needs inside the rubocop executable (gem "bundler", ">= 1.15.0" or whatever), and rescue the error and give a proper message if that fails. And in the case where bundler is already loaded by the time the executable is run, check for an appropriate Bundler::VERSION.

Also, shouldn't the warning be activated only if the user is actually using performance cops?

[koic]

@deivid-rodriguez Right! Thanks for your feedback.

Also, shouldn't the warning be activated only if the user is actually using performance cops?

I opened a PR #6944 that removes a warning when running rubocop command. In the future, it wll be better to replace it with a mechanism that displays a warning only when the user need Performance. Thank you, again!

[deivid-rodriguez]

No problem, thanks to you for your good work!

[agraul]

Rubocop failed for older bundlers because "Bundle dependencies" were change to be a Hash instead of an Array in: rubygems/bundler@9febe9a

Fix is here:agraul@09e0a90. It may help when bringing this back only for the case the user need Performance without having to require a newer Bundler.