AyuGramDesktop/Telegram/SourceFiles/iv/markdown

Native Markdown Instant View

This directory contains the native Markdown Instant View proof of concept behind TDESKTOP_NATIVE_MARKDOWN_IV.

Current scope:

• local .md / .markdown interception from the saved-document open flow
• UTF-8 validation plus explicit parser limits
• cmark-gfm parsing with tables, task lists, strikethrough, autolinks, tagfilter, and footnotes
• native prepare/layout/paint for paragraphs, lists, quotes, code blocks, tables, details blocks, and math
• MicroTeX-backed formula rendering with a preview-lifetime cache
• selection, copy, Copy Link, and Open Link actions inside the native preview

Build

The feature is compiled only when TDESKTOP_NATIVE_MARKDOWN_IV=ON.

For the app build, use a Debug tree:

cmake --build out --config Debug --target Telegram

The regression probe is emitted only when the build tree is also configured with DESKTOP_APP_TEST_APPS=ON. In that case:

cmake --build out --config Debug --target test_markdown_iv
out\Debug\test_markdown_iv.exe

Manual smoke test

1. Build a Debug app with TDESKTOP_NATIVE_MARKDOWN_IV=ON.
2. Launch Telegram Desktop from that build.
3. Save or download a local Markdown file.
4. Click the local .md or .markdown document from chat history.

Expected behavior:

• supported local Markdown opens in the native preview
• validation, parse, or unsupported-document rejection falls back to the normal file open path
• terminal post-open prepare failures show Can't preview this Markdown file with an Open file action

Useful manual checks:

• drag selection across multiple blocks
• copy inline math, display math, code blocks, and tables
• verify Copy Link / Open Link on external, anchor, footnote, and local-Markdown links
• verify rejected relative links do not expose an open action

Regression target coverage

test_markdown_iv now exercises both parser and prepare/render layers:

• parses markdown-example.md and latex-markdown-test.md
• checks known inline/display formula counts
• keeps the currency, escaped-dollar, fenced-code, and inline-code exclusions
• asserts inline-formula copySource, display-math formulaTex, details/footnote preservation, and link classification
• verifies oversized-table flattening diagnostics
• runs a headless MicroTeX render/cache smoke pass twice through the same renderer and checks second-pass cache hits

Limits and failure policy

Current hard limits:

• source bytes: 4 MiB
• cmark nodes: 100000
• nesting depth: 128
• formula bytes: 64 KiB
• formula count: 10000
• prepared blocks: 4096
• rendered table rows / columns / cells: 128 / 16 / 1024
• display-math logical render cap: 1600 x 1200
• formula image cap: 128 MiB physical image budget
• formula cache budget: 32 MiB per preview renderer

Policy:

• oversized or invalid sources reject before native open and fall back to normal file open
• oversized tables flatten into fallback blocks with diagnostics instead of failing the whole preview
• formula overflow or render failure falls back per formula and keeps the preview alive
• terminal prepare failures, including the prepared-block budget, switch the preview surface to the user-facing failure state

Known gaps

• preview entry is local-file-only; message-bubble embedding is still future work
• details-body reparsing still falls back to plain paragraph text when nested formulas or footnotes would be introduced
• table interaction supports per-cell text selection and whole-table copy, but not arbitrary rectangular multi-cell selection
• relative links are accepted only when they resolve to safe local Markdown targets under the source directory