1 files changed, 45 insertions, 3 deletions

diff --git a/packages/backend/src/core/MfmService.ts b/packages/backend/src/core/MfmService.ts
index dc47e38562..6c2f673217 100644
--- a/packages/backend/src/core/MfmService.ts
+++ b/packages/backend/src/core/MfmService.ts
@@ -179,6 +179,40 @@ export class MfmService {
 					break;
 				}
 
+					// this is here only to catch upstream changes!
+				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} ${rt}]`;
+					}
+					break;
+				}
+
 				// block code (<pre><code>)
 				case 'pre': {
 					if (node.childNodes.length === 1 && node.childNodes[0].nodeName === 'code') {
@@ -277,16 +311,24 @@ export class MfmService {
 								continue;
 							}
 							if (child.nodeName === 'rt') {
-								text += '$[ruby $[group ';
+								// the only case in which we don't need a `$[group ]`
+								// is when both sides of the ruby are simple words
+								const needsGroup = nonRtNodes.length > 1 ||
+									/\s|\[|\]/.test(getText(nonRtNodes[0])) ||
+									/\s|\[|\]/.test(getText(child));
+								text += '$[ruby ';
+								if (needsGroup) text += '$[group ';
 								appendChildren(nonRtNodes);
-								text += '] ';
+								if (needsGroup) text += ']';
+								text += ' ';
 								analyze(child);
-								text += '] ';
+								text += ']';
 								nonRtNodes = [];
 								continue;
 							}
 							nonRtNodes.push(child);
 						}
+						appendChildren(nonRtNodes);
 					}
 					break;
 				}