src/vs/editor/contrib/snippet/snippetParser.ts/TextmateSnippet/resolveVariables
class TextmateSnippet:	resolveVariables(resolver: VariableResolver): this {
		this.walk(candidate => {
			if (candidate instanceof Variable) {
				if (candidate.resolve(resolver)) {
					this._placeholders = undefined;
				}
			}
			return true;
		});
		return this;
	}