Fails to navigate to Markdown headers containing extended Unicode characters generated via autocomplete

[COPAPascal]

Type: Bug

Description

VS Code cannot reliably navigate to Markdown headers in the Markdown preview when using a link generated by autocomplete for a header that contains extended Unicode characters (e.g., 🔥, ✔️).

This happens whether the Unicode character appears at the end of the header or anywhere within it.

It remains unclear whether the problem lies in:

• link generation by autocomplete,
• the Markdown preview’s anchor resolution,
• or a combination of these.

---

Steps to Reproduce

1. Create a new text file.
2. Add several lines of filler text.
3. At the bottom, add the header ## 🔥Some header.
4. At the top of the file, type [link](# and select the 'Some header' anchor from autocomplete.
5. Open the preview (Markdown: Open Preview to the Side).
6. Click the link.
   → The preview does not navigate to the header.

Actual Behavior

The link does not navigate to the header.

Expected Behavior

Autocomplete-generated links should correctly navigate to autocomplete-generated headers in the preview.

Additional hint

If fixed, also test with ✔️. This character behaves differently: when a Variation Selector-16 is present, hidden symbols may be added to the generated link text.

VS Code version: Code 1.106.3 (bf9252a, 2025-11-25T22:28:18.024Z)
OS version: Windows_NT x64 10.0.26100
Modes:

System Info

Item	Value
CPUs	13th Gen Intel(R) Core(TM) i7-1365U (12 x 2688)
GPU Status	2d_canvas: enabled direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off trees_in_viz: disabled_off video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	undefined
Memory (System)	31.69GB (14.31GB free)
Process Argv	--crash-reporter-id 61268690-3e96-4352-a66a-cf1e9fadc69a
Screen Reader	no
VM	0%

Extensions (15)

Extension	Author (truncated)	Version
insert-unicode	bru	0.15.1
vscode-markdownlint	Dav	0.60.0
pb-syntax	flo	0.2.2
copilot	Git	1.388.0
copilot-chat	Git	0.33.3
vscode-drawio	hed	1.9.0
git-graph	mhu	1.30.0
vscode-language-pack-de	MS-	1.106.2025111209
debugpy	ms-	2025.16.0
python	ms-	2025.18.0
vscode-pylance	ms-	2025.10.3
vscode-python-envs	ms-	1.12.0
vscode-yaml	red	1.19.1
pdf	tom	1.2.2
markdown-pdf	yza	1.5.0

A/B Experiments

vsliv368cf:30146710
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
aj953862:31281341
nes-set-on:31351930
6abeh943:31336334
editstats-enabled:31346257
gaj49834:31404438
cloudbuttont:31379625
todos-1:31405332
v66_all_req:31402695
control_gpt5applypatchexclusively:31412085
3efgi100_wstrepl:31403338
trigger-command-fix:31379601
auto_model_enabled:31385282
use-responses-api:31390855
sonnet_45_3e700918:31424416
je187915:31401257
v2prompt_9f72f763:31415580
2a0ce269:31419925
agentic_ask_h7d75428:31408710
ec5jj548:31422691
copilot-nes-oct-t:31418199
terminalsuggestdisabled:31426256
cmp-ext-control:31426504
cp_cls_c_966_ss:31426491
chatvisible:31426294
defaulttokens:31426298
c0683394:31419495
g0h3h215:31426582
478ah919:31426277

[COPAPascal]

Facts after resarched more in detail

In summary: Only the HTML preview needs to be fixed:

• VSCode link generation with auto complete

  • The link style (slug) seems to be equal to how GitHub does (✅ good)
  • The Variation Selector-16 part of some unicode symbols (U+FE0F - like in ✔️) is not removed for auto complete link generation: This part (e.g. UTF-8: EF B8 8F) is put into the markdown link text (invisible character for the consumer). I first thought this would be wrong but depending on the renderer this is ok: Aligned to GitHub this invisible character needs to be kept, since GitHub's renderer creates
    • An HTML header whose id attribute contains this character
    • A link like e.g. <a href="#header7-%EF%B8%8F">Link to Header7</a> that also assumes this invisible character to be available.
      So according to GitHub this is also ✅ good and should not be changed

• VSCode Preview

  • This is the part where the issue lies I think. Seems that in the generated HTML for the preview either the links and/or the header (<hX>) do not consider the hidden characters like the GitHub renderer does. (not good ❌)
  • VSCode's preview should work with the links its own autocomplete creates:
    • Put the characters of the link in the HTML header id tags
    • Put the characters of the link in the HTML href attributes accordingly

Links generated by VSCode autocomplete

• These are the links created by VSCode autocomplete
• None of them work in VSCode preview (use the markdown of this comment)
• All of them work on GitHub (use the markdown of this comment and put into a new file)
• Links 7–12 contain invisible Variation Selector-16 U+FE0F characters because of ✔️.

Link to Header1
Link to Header2
Link to Header3
Link to Header4
Link to Header5
Link to Header6

Link to Header7
Link to Header8
Link to Header9
Link to Header10
Link to Header11
Link to Header12

Test-Header

Testing different headers types

• Symbol at the end with leading empty character
• Symbol at the end without leading empty character
• Symbol at the beginning followed by an empty character
• Symbol at the beginning without following empty character
• Symbol at the middle without leading empty character
• Symbol at the middle with leading empty character

For each type testing symbols

1. 🔥 (U+1F525)
2. ✔️ (contains Variation Selector-16 → U+2714 + U+FE0F)

Header1 🔥

Header2🔥

🔥 Header3

🔥Header4

Header🔥5

Header 🔥6

---

Header7 ✔️

Header8✔️

✔️ Header9

✔️Header10

Header✔️11

Header ✔️12

[mjbvz]

Should be fixed by #282556