Rails 7 1 support

[cowlibob]

Rails 7.1 appears to have changed what is passed into the MailDown::MarkdownEngine#to_html. What used to be a String (or String-like object) is now an ActionView::OutputBuffer.

ActionView::OutputBuffer does not respond to encode, valid_encoding? and other String methods called inside Kramdown.

The simplest fix I could muster is to convert to a String before use. Do feel free to consider other solutions though, if you feel it appropriate.

Using the gemfiles/rails_7_1_gemfile and it's lock without the fix (commit b520fae) will show the following (truncated) output during tests:

Error:
LayoutsTest#test_layout_renders_fine:
ActionView::Template::Error: undefined method `valid_encoding?' for an instance of ActionView::OutputBuffer
    kramdown (2.4.0) lib/kramdown/parser/base.rb:92:in `adapt_source'
    kramdown (2.4.0) lib/kramdown/parser/kramdown.rb:90:in `parse'
    kramdown-parser-gfm (1.1.0) lib/kramdown/parser/gfm.rb:56:in `parse'
    kramdown (2.4.0) lib/kramdown/parser/base.rb:69:in `parse'
    kramdown (2.4.0) lib/kramdown/document.rb:102:in `initialize'
    /Users/james/Projects/James/maildown/lib/maildown/markdown_engine.rb:53:in `new'
    /Users/james/Projects/James/maildown/lib/maildown/markdown_engine.rb:53:in `block in default_html_block'
    /Users/james/Projects/James/maildown/lib/maildown/markdown_engine.rb:24:in `to_html'
    app/views/user_with_layout_mailer/welcome.md+erb:1
    actionview (7.1.2) lib/action_view/base.rb:264:in `public_send'
    actionview (7.1.2) lib/action_view/base.rb:264:in `_run'
    actionview (7.1.2) lib/action_view/template.rb:261:in `block in render'

LayoutsTest#test_no_layout:
ActionView::Template::Error: undefined method `valid_encoding?' for an instance of ActionView::OutputBuffer
    kramdown (2.4.0) lib/kramdown/parser/base.rb:92:in `adapt_source'
    kramdown (2.4.0) lib/kramdown/parser/kramdown.rb:90:in `parse'
    kramdown-parser-gfm (1.1.0) lib/kramdown/parser/gfm.rb:56:in `parse'
    kramdown (2.4.0) lib/kramdown/parser/base.rb:69:in `parse'
    kramdown (2.4.0) lib/kramdown/document.rb:102:in `initialize'
    /Users/james/Projects/James/maildown/lib/maildown/markdown_engine.rb:53:in `new'
    /Users/james/Projects/James/maildown/lib/maildown/markdown_engine.rb:53:in `block in default_html_block'
    /Users/james/Projects/James/maildown/lib/maildown/markdown_engine.rb:24:in `to_html'
    app/views/user_no_layout_mailer/welcome.md+erb:1
    actionview (7.1.2) lib/action_view/base.rb:264:in `public_send'
    actionview (7.1.2) lib/action_view/base.rb:264:in `_run'
    actionview (7.1.2) lib/action_view/template.rb:261:in `block in render'

Running the same test suit on (commit 2347d47) will pass.

[joshuapinter]

Hey @schneems, any chance we can get this looked and merged in, if good. We're in the process of upgrading to Rails 7.1 and this is a super useful gem we use to DRY up a tonne of our views.

Let me know what I can do to help too.

Thanks!