mdx.validate.validateFileLinks does not show diagnostics

[karlhorky]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Affected packages and versions

MDX VS Code Extension v1.8.9

Link to runnable example

No response

Steps to reproduce

1. Open app/message.mdx in the reproduction repo (code below)
2. Observe that none of the 4 "incorrect path" permutations for the non-existent file mdx2.png report any diagnostics (both images and links, relative paths starting with ./ and "bare" paths without any ./)

## Links

[link relative](./mdx.png) and [link bare](mdx.png)

[link relative - incorrect path](./mdx2.png) and [link bare - incorrect path](mdx2.png)

## Images

![image relative](./mdx.png) and ![image bare](mdx.png)

![image relative - incorrect path](./mdx2.png) and ![image bare - incorrect path](mdx2.png)

Expected behavior

Diagnostics and problems should be reported for non-existent files when mdx.validate.validateFileLinks is set to hint, warning or error

Actual behavior

Diagnostics and problems are not reported for non-existent files when mdx.validate.validateFileLinks is set to hint, warning or error

Runtime

No response

Package manager

No response

OS

macOS

Build and bundle tools

No response

[polynook]

I can observe the same behavior.

In my case, from all available validations, only one works, and that is the link.no-such-reference.
The link.no-such-header-in-file validation also reports, although incorrectly—it reports an error when the header exists.

mdx.mdx file content:

[no-definition] {/* No link definition found: 'no-definition'(link.no-such-reference) */}
[empty-definition]()

[non-existing-file-relative](./not-existing-file)
[non-existing-file-absolute](not-existing-file)

[existing-file-relative](./existing-file.md)
[existing-file-absolute](/existing-file.md)

[existing-file-existing-header](./existing-file.md#existing-header) {/* Header does not exist in file: existing-header(link.no-such-header-in-file) */}
[existing-file-non-existing-header](./existing-file.md#non-existing-header) {/* Header does not exist in file: non-existing-header(link.no-such-header-in-file) */}

[non-existing-file-non-existing-header](./not-existing-file#non-existing-header)
[non-existing-file-non-existing-header](not-existing-file#non-existing-header)
- Header does not exist in file: my_file(link.no-such-header-in-file)

I used the exact same content in an md.md file as control, and all Markdown validations work with plain VS Code Markdown (except for [empty-definition]() not being flagged as no-definition, which I personally think should be flagged as such).

I did this test in a blank VS Code profile that has only MDX extension installed to exclude possible conflicts.