fix(backend): Let MfmService.fromHtml accept ruby (#15117)

This fix makes `MfmService.fromHtml()` method accept `<ruby>` tags
and translate it to MFM's ruby characters syntax (`$[ruby ...]`).

このパッチは`MfmService.fromHtml()`メソッドが`<ruby>`タグをMFMの
読み仮名（ルビ）文法に翻訳する様に修正します。

1 files changed, 33 insertions, 0 deletions

diff --git a/packages/backend/src/core/MfmService.ts b/packages/backend/src/core/MfmService.ts
index 8061622340..bf06d4457e 100644
--- a/packages/backend/src/core/MfmService.ts
+++ b/packages/backend/src/core/MfmService.ts
@@ -171,6 +171,39 @@ export class MfmService {
 					break;
 				}
 
+				case 'ruby': {
+					let ruby: [string, string][] = [];
+					for (const child of node.childNodes) {
+						if (child.nodeName === 'rp') {
+							continue;
+						}
+						if (treeAdapter.isTextNode(child) && !/\s|\[|\]/.test(child.value)) {
+							ruby.push([child.value, '']);
+							continue;
+						}
+						if (child.nodeName === 'rt' && ruby.length > 0) {
+							const rt = getText(child);
+							if (/\s|\[|\]/.test(rt)) {
+								// If any space is included in rt, it is treated as a normal text
+								ruby = [];
+								appendChildren(node.childNodes);
+								break;
+							} else {
+								ruby.at(-1)![1] = rt;
+								continue;
+							}
+						}
+						// If any other element is included in ruby, it is treated as a normal text
+						ruby = [];
+						appendChildren(node.childNodes);
+						break;
+					}
+					for (const [base, rt] of ruby) {
+						text += `$[ruby ${base} ${rt}]`;
+					}
+					break;
+				}
+
 				// block code (<pre><code>)
 				case 'pre': {
 					if (node.childNodes.length === 1 && node.childNodes[0].nodeName === 'code') {