Sourced from haml's changelog.

5.0.0

Released on April 26, 2017
(diff).

Breaking Changes

• Haml now requires Ruby 2.0.0 or above.

• Rails 3 is no longer supported, matching the official
  Maintenance Policy for Ruby on Rails.
  Use Haml 4 if you want to use Rails 3.
  (Tee Parham)

• Remove :ugly option (#894)

• The haml command's debug option (-d) no longer executes the Haml code, but
  rather checks the generated Ruby syntax for errors.

• Drop parser/compiler accessor from Haml::Engine. Modify Haml::Engine#initialize options
  or Haml::Template.options instead. (Takashi Kokubun)

• Drop dynamic quotes support and always escape ' for escape_html/escape_attrs instead.
  Also, escaped results are slightly changed and always unified to the same characters. (Takashi Kokubun)

• Don't preserve newlines in attributes. (Takashi Kokubun)

• HTML escape interpolated code in filters.
  #770
  (Matt Wildig)

    :javascript
      #{JSON.generate(foo: "bar")}
    Haml 4 output: {"foo":"bar"}
    Haml 5 output: {"foo":"bar"}
  

Added

• Add a tracing option. When enabled, Haml will output a data-trace attribute on each tag showing the path
  to the source Haml file from which it was generated. Thanks Alex Babkin.
• Add haml_tag_if to render a block, conditionally wrapped in another element (Matt Wildig)
• Support Rails 5.1 Erubi template handler.
• Support Sprockets 3. Thanks Sam Davies and Jeremy Venezia.
• General performance and memory usage improvements. (Akira Matsuda)
• Analyze attribute values by Ripper and render static attributes beforehand. (Takashi Kokubun)
• Optimize attribute rendering about 3x faster. (Takashi Kokubun)
• Add temple gem as dependency and create Haml::TempleEngine class.
  Some methods in Haml::Compiler are migrated to Haml::TempleEngine. (Takashi Kokubun)

Fixed

• Fix for attribute merging. When an attribute method (or literal nested hash)
  was used in an old style attribute hash and there is also a (non-static) new
  style hash there is an error. The fix can result in different behavior in
  some circumstances. See the commit message
  for detailed info. (Matt Wildig)
• Make escape_once respect hexadecimal references. (Matt Wildig)

... (truncated)

• 78e2a09 Version 5.0.0
• e5d6409 Note about #770 in Haml 5 changes
• 1bac6f9 Remove JRuby from allow_failures
• d45c2d4 Add backslash for @ to support JRuby
• 8f20707 Enable frozen_string_literal pragma if possible
• a6bb255 Oops, this was not intentional...
• aa4c397 Fix spec in #867 for pretty mode removal
• 11af795 Fallback to default value of preserve option
• bbbeb7e Update CHANGELOG to include #867
• ed7f24f Merge pull request #867 from redoPop/atful-css
• Additional commits viewable in compare view

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