Markdown footnote validation

[mail2nnv]

Does this issue occur when all extensions are disabled?: Yes/No
Yes

• VS Code Version: 1.73.1
• OS Version: Windows_NT x64 10.0.19044

Steps to Reproduce:

1. Create new markdown file
2. Type a text:

text[^1]
[^1]: footnote

3. See problems:
   (×) No link definition found: '^1' (link.no-such-reference) [Ln 1, Col 6]
   

[GeorgyKwe]

Try separating footnotes and citations by one line.

[mail2nnv]

Try separating footnotes and citations by one line.

Nothing changed.

[benblank]

I'm sure this needs a more thorough look from someone familiar with the parser, but a quick check suggests that this behavior is the result of a conflict between how reference links are parsed and how link definitions are parsed.

Specifically, link definitions are explicitly not recognized if the reference name starts with a caret. (Note the (?!\^).)

vscode-markdown-languageservice/src/languageFeatures/documentLinks.ts

Line 323 in 984eeb7

const definitionPattern = /^([\t ]*\[(?!\^)((?:\\\]|[^\]])+)\]:\s*)([^<]\S*|<[^>]+>)/gm;

Conversely, reference links aren't subject to that exclusion. (Called out here as the "link def".)

vscode-markdown-languageservice/src/languageFeatures/documentLinks.ts

Lines 295 to 313 in 984eeb7

	const referenceLinkPattern = new RegExp(
	r`(^|[^\]\\])` + // Must not start with another bracket (workaround for lack of support for negative look behinds)
	r`(?:` +
	/**/r`(?:` +
	/****/r`(` + // Start link prefix
	/******/r`!?` + // Optional image ref
	/******/r`\[((?:` +// Link text
	/********/r`\\\]|` + // escaped bracket, or...
	/********/r`[^\[\]]|` + //non bracket char, or...
	/********/r`\[[^\[\]]*\]` + // matched bracket pair
	/******/`+)*)\]` + // end link text
	/******/r`\[\s*?` + // Start of link def
	/****/r`)` + // end link prefix
	/****/r`(` +
	/******/r`[^\]]*?)\]` + //link def
	/******/r`|` +
	/******/r`\[\s*?([^\\\]]*?)\s*\])(?![\(])` +
	r`)`,
	'gm');

As a result, footnotes appear to be interpreted as [shorthand]-style reference links which simply happen to start with a caret. But because the matching footnote definition isn't recognized as a link definition, the language service sees this as a link without a definition.

By my read, a fix for this could be as simple as removing (?!\^) from definitionPattern. Unless there's something else in the way, that should allow the parser to find the link definition. It'll still think the footnote is a link, though, and I don't know whether that could cause other issues.

[villeodell]

Just for additional context, even though most people's use case for this is footnotes, the following minimal example is parsed fine by commonmark.js (see here)

[^1]

[^1]: /url

However, vscode complains with

No link definition found: '^1'(link.no-such-reference)

[hellt]

footnotes are often used in rich documentation sites powered by mkdocs and the likes. Would be great to see this fixed

a few examples with footnotes that are not captured as a link in the current vscode markdown lsp:

[`Makefile`][makefile][^1]

`make`[^4]

[`text`](url)[^5]