yaml parser: support `#` in literal

[aelij]

• Copilot Chat Extension Version: 0.35.2025120802
• VS Code Version: 1.107.0-insider
• OS Version: 25H2
• Feature (e.g. agent/edit/ask mode): Agent
• Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet): Claude Opus 4.5
• Logs:

From Chat Debug:

<instruction>
<description>C</description>
<file>repo-path/.github/instructions/style.instructions.md</file>
<applyTo>**</applyTo>
</instruction>

style.instructions.md frontmatter:

---
description: C# coding conventions
applyTo: "**"
---

Steps to Reproduce:

1. Add an .instructions.md file with a special character in the description frontmatter, e.g. description: C# coding conventions
2. Write a chat message in Agent mode

[aeschli]

It's a bug, but please for now put quotes around the name. # is the comment token in YAML and the parser starts a coment.

[aelij]

Is this a reasonable fix?

		const isTerminator = (char: string): boolean => {
			// Comments must be preceded by whitespace
			if (char === '#') {
				const prevChar = this.lexer.getPreviousChar();
				return prevChar === '' || isWhitespace(prevChar);
			}
			// Comma, ']' and '}' only terminate inside flow collections
			if (this.flowLevel > 0 && (char === ',' || char === ']' || char === '}')) { return true; }
			return false;
		};

[RedCMD]

even tho # is YAML's comment token
a # by itself is not a valid comment
is must be preceded by a whitespace char \r\n\t

@aelij

Comma, ']' and '}' only terminate inside flow collections

afaik they don't?

[aelij]

@RedCMD this was existing code, I only added the part that checks that # is preceded by whitespace.

vscode/src/vs/base/common/yaml.ts

Lines 326 to 332 in 01586ca

	// Helper function to check for value terminators
	const isTerminator = (char: string): boolean => {
	if (char === '#') { return true; }
	// Comma, ']' and '}' only terminate inside flow collections
	if (this.flowLevel > 0 && (char === ',' || char === ']' || char === '}')) { return true; }
	return false;
	};

From what I gather isTerminator is not just checking for comments, it checks if we reached the end of a value. But I'm just a guest here.

[RedCMD]

I see now

your fix seems perfectly reasonable