Doppeltes Entkommen von Unterstrichen im Alt-Text von Bildern beschädigt den Roh-Beitrag bei jeder Bearbeitung

zogstrip · 23. April 2026 um 08:41

Das ist eine knifflige Angelegenheit

github.com/discourse/discourse

FIX: Prevent backslash accumulation in upload markdown labels (#39461)

main ← fix-upload-label-escape-doubling

opened 05:00PM - 22 Apr 26 UTC

ZogStriP

+221 -46

in upload filenames at generation time. That worked for freshly uploaded files b…ut exposed a latent bug in the rich-editor round-trip: markdown-it kept `\_` in the parsed image token's content, ProseMirror stored it verbatim in the `alt` attribute, and on save the serializer re-escaped each `\` to `\\`. Every edit doubled the backslashes (1 → 2 → 4 → … → 2^N) until the post exceeded `max_post_length` and became uneditable. **Approach change** Escaping the raw is fundamentally fragile — nothing treats the stored raw as canonical, so any parse/serialize cycle either drops the escape or re-applies it. Fix it at parse time instead: - Revert the generation-side escaping from #39133 in `UploadMarkdown`, `uploads.js`, `inline_uploads.rb`, `to-markdown.js`, and `sanitizeAlt`. - Add a `literalize_upload_labels` core ruler in the markdown-it engine. After inline parsing runs, it walks `image` / `link_open` tokens whose URL starts with `upload://` and collapses their children into a single literal text token. The label text is reconstructed from children `content` plus the `markup` of emphasis/strong/strikethrough delimiters, so `_foo_`, `**foo**`, `~~foo~~`, `` `foo` ``, `\_foo`, linkified URLs, hashtags, mentions, and emoji shortcodes inside upload labels all render literally. The raw now stays canonical — the filename goes in verbatim, cooks the same way on every pass, and both the textarea and rich editor round-trip identically. Reference-style links (`[label][ref]` with `[ref]: upload://…`) get the same treatment for free since they go through the same `link_open`/`image` tokens. **Parser resilience from #39133 is kept** The multi-token scan-forward in `renderAttachment` (engine.js) and in ProseMirror's `link.js` parser still matters for non-upload attachment links like `[**bold**|attachment](https://example.com/file.pdf)`, where the label legitimately contains inline formatting that the new ruler doesn't touch. **Data cleanup** `StripUploadLabelEscapes` (post-deploy migration) heals posts already damaged by the regression with a single scoped `regexp_replace`. The lookahead `(?=[^\]]*\]\(upload://)` bounds the match to upload labels so user-written `\_` escapes elsewhere in the raw stay intact. Excluding `\` from the prefix char class keeps the greedy match from swallowing a backslash that belongs to the run being stripped. https://meta.discourse.org/t/401231

Thema		Antworten	Aufrufe
Markdown rendering issue with image surrounded with HTML Bug	24	4203	4. April 2022
Uploads broken with subfolder installation Bug subfolder	6	618	2. September 2022
Thumbnail generation & markdown rendering issue Support	14	1986	30. Mai 2020
Duplicate emoji code in post blurb Bug	3	795	22. Juli 2022
How to find any missing images? Support	62	7104	31. Juli 2019

Doppeltes Entkommen von Unterstrichen im Alt-Text von Bildern beschädigt den Roh-Beitrag bei jeder Bearbeitung

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