fix(formatter): preserve remote MFM mentions

lib/pleroma/formatter.ex

@@ -129,6 +129,7 @@ defmodule Pleroma.Formatter do
 
   def markdown_to_html(text, opts) do
     breaks = Map.get(opts, :breaks, false)
+    strip_email_autolinks = Map.get(opts, :strip_email_autolinks, false)
     text = normalize_markdown_quirks(text)
 
     MDEx.new(
@@ -138,6 +139,7 @@ defmodule Pleroma.Formatter do
       render: [hardbreaks: breaks, unsafe: true]
     )
     |> MDEx.Document.run()
+    |> maybe_strip_email_autolinks(strip_email_autolinks)
     |> MDEx.Document.update_nodes(MDEx.HtmlBlock, &strip_dangerous_raw_html/1)
     |> MDEx.Document.update_nodes(MDEx.HtmlInline, &strip_dangerous_raw_html/1)
     |> MDEx.to_html!()
@@ -176,6 +178,24 @@ defmodule Pleroma.Formatter do
       String.ends_with?(markdown, ">")
   end
 
+  defp maybe_strip_email_autolinks(document, true) do
+    MDEx.Document.update_nodes(document, MDEx.Link, &strip_email_autolink/1)
+  end
+
+  defp maybe_strip_email_autolinks(document, _), do: document
+
+  defp strip_email_autolink(
+         %MDEx.Link{
+           nodes: [%MDEx.Text{literal: literal, sourcepos: text_sourcepos} = text],
+           url: "mailto:" <> email,
+           sourcepos: sourcepos
+         } = link
+       ) do
+    if email == literal and sourcepos == text_sourcepos, do: text, else: link
+  end
+
+  defp strip_email_autolink(link), do: link
+
   defp strip_dangerous_raw_html(%{literal: literal} = node) do
     literal =
       literal

lib/pleroma/web/common_api/utils.ex

@@ -324,7 +324,7 @@ defmodule Pleroma.Web.CommonAPI.Utils do
 
   def format_input(text, "text/x.misskeymarkdown", options) do
     text
-    |> Formatter.markdown_to_html(%{breaks: true})
+    |> Formatter.markdown_to_html(%{breaks: true, strip_email_autolinks: true})
     |> safe_mfm_to_html()
     |> Formatter.linkify(options)
     |> Formatter.html_escape("text/x.misskeymarkdown")

test/pleroma/web/activity_pub/object_validators/article_note_page_validator_test.exs

@@ -216,6 +216,39 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.ArticleNotePageValidatorTest
     assert content =~ "@uncached"
   end
 
+  test "a Misskey MFM remote mention is not rendered as an email link" do
+    remote_user = insert(:user, ap_id: "https://mk.absturztau.be/users/alice")
+    mentioned_user = insert(:user, ap_id: "https://movsw.0x0.st/users/bob")
+
+    note = %{
+      "id" => "https://mk.absturztau.be/notes/1",
+      "type" => "Note",
+      "actor" => remote_user.ap_id,
+      "attributedTo" => remote_user.ap_id,
+      "to" => ["https://www.w3.org/ns/activitystreams#Public"],
+      "cc" => [mentioned_user.ap_id],
+      "content" => ~s(<p>@<a href="mailto:bob@movsw.0x0.st">bob@movsw.0x0.st</a> hello</p>),
+      "context" => Utils.generate_context_id(),
+      "tag" => [
+        %{
+          "type" => "Mention",
+          "name" => "@bob@movsw.0x0.st",
+          "href" => mentioned_user.ap_id
+        }
+      ],
+      "source" => %{
+        "content" => "@bob@movsw.0x0.st hello",
+        "mediaType" => "text/x.misskeymarkdown"
+      }
+    }
+
+    %{valid?: true, changes: %{content: content}} =
+      ArticleNotePageValidator.cast_and_validate(note)
+
+    assert content =~ ~s(href="#{mentioned_user.ap_id}")
+    refute content =~ "mailto:"
+  end
+
   test "a Misskey MFM note drops oversized source content instead of parsing it" do
     user = insert(:user, ap_id: "https://misskey.example/users/oversized")
 

test/pleroma/web/common_api/utils_test.exs

@@ -125,6 +125,14 @@ defmodule Pleroma.Web.CommonAPI.UtilsTest do
       assert output == expected
     end
 
+    test "MFM keeps bare URLs containing Markdown delimiters intact" do
+      url = "https://example.org/a*b*c"
+
+      {output, [], []} = Utils.format_input(url, "text/x.misskeymarkdown")
+
+      assert output == ~s(<p><a href="#{url}">#{url}</a></p>)
+    end
+
     test "works for bare text/bbcode" do
       text = "[b]hello world[/b]"
       expected = "<strong>hello world</strong>"