src/vs/editor/common/languageSelector.ts/score
export function score(selector: LanguageSelector | undefined, candidateUri: URI, candidateLanguage: string, candidateIsSynchronized: boolean, candidateNotebookUri: URI | undefined, candidateNotebookType: string | undefined): number {

	if (Array.isArray(selector)) {
		// array -> take max individual value
		let ret = 0;
		for (const filter of selector) {
			const value = score(filter, candidateUri, candidateLanguage, candidateIsSynchronized, candidateNotebookUri, candidateNotebookType);
			if (value === 10) {
				return value; // already at the highest
			}
			if (value > ret) {
				ret = value;
			}
		}
		return ret;

	} else if (typeof selector === 'string') {

		if (!candidateIsSynchronized) {
			return 0;
		}

		// short-hand notion, desugars to
		// 'fooLang' -> { language: 'fooLang'}
		// '*' -> { language: '*' }
		if (selector === '*') {
			return 5;
		} else if (selector === candidateLanguage) {
			return 10;
		} else {
			return 0;
		}

	} else if (selector) {
		// filter -> select accordingly, use defaults for scheme
		const { language, pattern, scheme, hasAccessToAllModels, notebookType } = selector as LanguageFilter; // TODO: microsoft/TypeScript#42768

		if (!candidateIsSynchronized && !hasAccessToAllModels) {
			return 0;
		}

		// selector targets a notebook -> use the notebook uri instead
		// of the "normal" document uri.
		if (notebookType && candidateNotebookUri) {
			candidateUri = candidateNotebookUri;
		}

		let ret = 0;

		if (scheme) {
			if (scheme === candidateUri.scheme) {
				ret = 10;
			} else if (scheme === '*') {
				ret = 5;
			} else {
				return 0;
			}
		}

		if (language) {
			if (language === candidateLanguage) {
				ret = 10;
			} else if (language === '*') {
				ret = Math.max(ret, 5);
			} else {
				return 0;
			}
		}

		if (notebookType) {
			if (notebookType === candidateNotebookType) {
				ret = 10;
			} else if (notebookType === '*' && candidateNotebookType !== undefined) {
				ret = Math.max(ret, 5);
			} else {
				return 0;
			}
		}

		if (pattern) {
			let normalizedPattern: string | IRelativePattern;
			if (typeof pattern === 'string') {
				normalizedPattern = pattern;
			} else {
				// Since this pattern has a `base` property, we need
				// to normalize this path first before passing it on
				// because we will compare it against `Uri.fsPath`
				// which uses platform specific separators.
				// Refs: https://github.com/microsoft/vscode/issues/99938
				normalizedPattern = { ...pattern, base: normalize(pattern.base) };
			}

			if (normalizedPattern === candidateUri.fsPath || matchGlobPattern(normalizedPattern, candidateUri.fsPath)) {
				ret = 10;
			} else {
				return 0;
			}
		}

		return ret;

	} else {
		return 0;
	}
}