Add autocorrect

[FnControlOption]

User-facing changes:

• Added CLI flag --fix.
• Added autocorrect for Style/LargeNumbers and partially for Layout/TrailingBlankLines.
• Added optional block parameter to Reportable#add_issue. The block receives a Source::Corrector (described below) to perform autocorrection.
• Added expect_correction and expect_no_corrections spec helpers.

Implementation details:

• Added Source::Rewriter and Source::Rewriter::Action, which are ports of Parser::Source::TreeRewriter and Parser::Source::TreeRewriter::Action from the Ruby gem parser. These classes accept source positions as integer indexes (instead of line and column).
• Added Source::Corrector, which wraps around a Source::Rewriter. This class provides helper methods that accept source locations as Crystal::Location or {Int32, Int32}. (The length of each source line is stored in an array, which is used to convert AST locations to Rewriter positions.)

Changes required for recursive autocorrect (f39a7a4):

• Added Source#correct, which runs autocorrection and updates the underlying @code property.
• Issue.new now requires an additional code parameter (because Source#code is no longer immutable).
• Formatter::Util#affected_code now has an additional method overload.
  • The original method now receives a String as the first parameter instead of Source.
  • The new overload accepts an Issue so that we can now do affected_code(issue) instead of affected_code(issue.code, issue.location, issue.end_location)

Todo:

• Update other formatters in src/ameba/formatter to indicate whether any issues have been autocorrected.
• Add missing methods from RuboCop::Cop::Corrector: remove_preceding, remove_leading, remove_trailing
• Add documentation for:
  • Config#autocorrect
  • Runner#autocorrect
  • Source#correct
  • Source::Corrector and its methods
• Add :nodoc: directive to Source::Rewriter::Action since it is only used internally.

Future PRs:

• Implement policy configuration for different_replacements and swallowed_insertions (and maybe also crossing_deletions). I didn't realize that RuboCop::Cop::Corrector configures different_replacements and swallowed_insertions to :raise.
• Revert corrections if they produce a syntax error #discussion_r736176647

[FnControlOption]

Thank you for reviewing, @veelenga and @Sija. Now before I start working on the final todo, do you think it is necessary?

• Implement policy configuration for different_replacements and swallowed_insertions (and maybe also crossing_deletions).
  • I didn't realize that RuboCop::Cop::Corrector configures different_replacements and swallowed_insertions to :raise.

Or is what I have so far good enough, and this can be added in a follow-up pull request?

For reference, here's the relevant documentation: https://github.com/whitequark/parser/blob/master/lib/parser/source/tree_rewriter.rb#L59-L77
(rubydoc.info messes up the formatting)

[veelenga]

@FnControlOption I am fine moving this out of scope of this PR. Current work is big enough. Thanks

[veelenga]

I tested this locally and it is looking great. Thanks for you work @FnControlOption

I left two small suggestions/comments

[veelenga]

👏

[Sija]

🚀