Prevent premailer from converting HTML entities

This prevents `&mdash` in our templates being change to `-`

3 files changed, 20 insertions, 1 deletions

diff --git a/changelogs/unreleased/55964-fix-email-encoding.yml b/changelogs/unreleased/55964-fix-email-encoding.yml
new file mode 100644
index 00000000000..2195a853702
--- /dev/null
+++ b/changelogs/unreleased/55964-fix-email-encoding.yml
@@ -0,0 +1,5 @@
+---
+title: Fix notfication emails having wrong encoding
+merge_request: 26931
+author:
+type: fixed
diff --git a/config/initializers/premailer.rb b/config/initializers/premailer.rb
index cb00d3cfe95..87f8e67ef1c 100644
--- a/config/initializers/premailer.rb
+++ b/config/initializers/premailer.rb
@@ -4,5 +4,6 @@ Premailer::Rails.config.merge!(
   preserve_styles: true,
   remove_comments: true,
   remove_ids: false,
-  remove_scripts: false
+  remove_scripts: false,
+  output_encoding: 'US-ASCII'
 )
diff --git a/spec/mailers/notify_spec.rb b/spec/mailers/notify_spec.rb
index 3c8897ed37c..5fa1369c00a 100644
--- a/spec/mailers/notify_spec.rb
+++ b/spec/mailers/notify_spec.rb
@@ -30,6 +30,19 @@ describe Notify do
                    description: 'My awesome description!')
   end
 
+  describe 'with HTML-encoded entities' do
+    before do
+      described_class.test_email('test@test.com', 'Subject', 'Some body with —').deliver
+    end
+
+    subject { ActionMailer::Base.deliveries.last }
+
+    it 'retains 7bit encoding' do
+      expect(subject.body.ascii_only?).to eq(true)
+      expect(subject.body.encoding).to eq('7bit')
+    end
+  end
+
   context 'for a project' do
     shared_examples 'an assignee email' do
       it 'is sent to the assignee as the author' do