fix(markdown): don't convert underscore within urls or emails

app/components/simple_format_component.rb

@@ -21,12 +21,22 @@ class SimpleFormatComponent < ApplicationComponent
     no_images: true
   }
 
+  SIMPLE_URL_REGEX = %r{https?://\S+}
+  EMAIL_IN_TEXT_REGEX = Regexp.new(Devise.email_regexp.source.gsub(/\\A|\\z/, '\b'))
+
   def initialize(text, allow_a: true, class_names_map: {})
+    @allow_a = allow_a
+
     @text = (text || "").gsub(/\R/, "\n\n") # force double \n otherwise a single one won't split paragraph
       .split("\n\n")  #
       .map(&:lstrip)  # this block prevent redcarpet to consider "   text" as block code by lstriping
-      .join("\n\n")   #
-    @allow_a = allow_a
+      .join("\n\n")
+      .gsub(EMAIL_IN_TEXT_REGEX) { _1.gsub('_', '\\_') } # Workaround for redcarpet bug on autolink email having _. Cf tests
+
+    if !@allow_a
+      @text = @text.gsub(SIMPLE_URL_REGEX) { _1.gsub('_', '\\_') } # Escape underscores in URLs
+    end
+
     @renderer = Redcarpet::Markdown.new(
       Redcarpet::BareRenderer.new(class_names_map:),
       REDCARPET_EXTENSIONS.merge(autolink: @allow_a)

app/lib/redcarpet/bare_renderer.rb

@@ -26,6 +26,7 @@ module Redcarpet
       when :url
         link(link, nil, link)
       when :email
+        # NOTE: As of Redcarpet 3.6.0, autolinking email containing is broken https://github.com/vmg/redcarpet/issues/402
         content_tag(:a, link, { href: "mailto:#{link}" })
       else
         link

spec/components/simple_format_component_spec.rb

@@ -90,4 +90,31 @@ TEXT
       it { expect(page).not_to have_selector("a") }
     end
   end
+
+  context 'emphasis not in urls' do
+    let(:text) do
+      <<~TEXT
+        A _string emphased_ but https://example.fr/path_preserves_underscore
+        email: here_is_my@email.com
+      TEXT
+    end
+
+    context "without autolink" do
+      let(:allow_a) { false }
+      it { expect(page).to have_selector("em", count: 1, text: "string emphased") }
+      it { expect(page).to have_text("https://example.fr/path_preserves_underscore") }
+      it { expect(page).to have_text("email: here_is_my@email.com") }
+    end
+
+    context "with autolink" do
+      let(:allow_a) { true }
+      it {
+        expect(page).to have_link("https://example.fr/path_preserves_underscore")
+
+        # NOTE: As of Redcarpet 3.6.0, autolinking email containing _ is broken https://github.com/vmg/redcarpet/issues/402
+        # but we still want the email to be displayed
+        expect(page).to have_text("here_is_my@email.com")
+      }
+    end
+  end
 end