fix: keep blank lines when pasting plain text into the composer

components/email/__tests__/plain-text-paste.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, it } from 'vitest';
+import { Editor } from '@tiptap/core';
+import StarterKit from '@tiptap/starter-kit';
+
+import { PlainTextPaste } from '../plain-text-paste';
+
+function makeEditor(content = '<p></p>') {
+  return new Editor({
+    element: document.createElement('div'),
+    extensions: [StarterKit, PlainTextPaste],
+    coreExtensionOptions: { clipboardTextSerializer: { blockSeparator: '\n' } },
+    content,
+  });
+}
+
+// jsdom has no ClipboardEvent, which pasteText constructs when given none.
+function paste(editor: Editor, text: string) {
+  editor.view.pasteText(text, new Event('paste') as ClipboardEvent);
+}
+
+describe('plain-text paste', () => {
+  it('keeps blank lines as empty paragraphs', () => {
+    const editor = makeEditor();
+    paste(editor, 'Hi Joost,\n\nThanks for the write-up.\n\n\nPHASE 1');
+    expect(editor.getHTML()).toBe(
+      '<p>Hi Joost,</p><p></p><p>Thanks for the write-up.</p><p></p><p></p><p>PHASE 1</p>',
+    );
+    editor.destroy();
+  });
+
+  it('treats CRLF and CR line endings like LF', () => {
+    const editor = makeEditor();
+    paste(editor, 'one\r\n\r\ntwo\rthree');
+    expect(editor.getHTML()).toBe('<p>one</p><p></p><p>two</p><p>three</p>');
+    editor.destroy();
+  });
+
+  it('pastes a single line inline without splitting the paragraph', () => {
+    const editor = makeEditor('<p>Hello world</p>');
+    editor.commands.setTextSelection(7);
+    paste(editor, 'big ');
+    expect(editor.getHTML()).toBe('<p>Hello big world</p>');
+    editor.destroy();
+  });
+
+  it('copies back out as the same text', () => {
+    const text = 'Hi Joost,\n\nThanks for the write-up.\n\n\nPHASE 1';
+    const editor = makeEditor();
+    paste(editor, text);
+    // TipTap's serializer reads the editor selection, not the slice it gets.
+    editor.commands.selectAll();
+    const slice = editor.state.selection.content();
+    const copied = editor.view.someProp('clipboardTextSerializer', (f) => f(slice, editor.view));
+    expect(copied).toBe(text);
+    editor.destroy();
+  });
+});

components/email/plain-text-paste.ts

@@ -0,0 +1,36 @@
+import { Extension } from "@tiptap/core";
+import { Fragment, Slice } from "@tiptap/pm/model";
+import { Plugin, PluginKey } from "@tiptap/pm/state";
+
+/**
+ * Pastes plain text as one paragraph per line, blank lines included.
+ *
+ * In the composer Enter starts a new paragraph and a blank line is an empty
+ * paragraph. ProseMirror's default text paste splits on runs of newlines
+ * instead, so every blank line was dropped and a pasted mail arrived as a
+ * wall of lines with no gap between its paragraphs. This builds the same
+ * paragraphs typing the text would.
+ */
+export const PlainTextPaste = Extension.create({
+  name: "plainTextPaste",
+
+  addProseMirrorPlugins() {
+    const { schema } = this.editor;
+    return [
+      new Plugin({
+        key: new PluginKey("plainTextPaste"),
+        props: {
+          clipboardTextParser: (text, $context) => {
+            const marks = $context.marks();
+            const paragraphs = text
+              .split(/\r\n?|\n/)
+              .map((line) =>
+                schema.nodes.paragraph.create(null, line ? schema.text(line, marks) : null),
+              );
+            return Slice.maxOpen(Fragment.from(paragraphs));
+          },
+        },
+      }),
+    ];
+  },
+});

components/email/rich-text-editor.tsx

@@ -9,6 +9,7 @@ import Underline from "@tiptap/extension-underline";
 import Link from "@tiptap/extension-link";
 import TextAlign from "@tiptap/extension-text-align";
 import { TextDirection } from "@/components/email/text-direction";
+import { PlainTextPaste } from "@/components/email/plain-text-paste";
 import { TextStyle, BackgroundColor } from "@tiptap/extension-text-style";
 import Color from "@tiptap/extension-color";
 import { FontSize, FONT_SIZES } from "@/components/email/font-size";
@@ -236,7 +237,14 @@ export function RichTextEditor({
       // into editable content (#822).
       SignatureBlock.configure({ editHint: tComposer('signature_edit_hint') }),
       TextDirection,
+      PlainTextPaste,
     ],
+    // One newline per paragraph when copying out as plain text, the inverse
+    // of PlainTextPaste: a blank line is an empty paragraph, so the default
+    // "\n\n" separator doubled every line break.
+    coreExtensionOptions: {
+      clipboardTextSerializer: { blockSeparator: "\n" },
+    },
     content,
     editorProps: {
       attributes: {