src/vs/workbench/contrib/files/browser/views/explorerDecorationsProvider.ts/provideDecorations
export function provideDecorations(fileStat: ExplorerItem): IDecorationData | undefined {
	if (fileStat.isRoot && fileStat.isError) {
		return {
			tooltip: localize('canNotResolve', "Unable to resolve workspace folder"),
			letter: '!',
			color: listInvalidItemForeground,
		};
	}
	if (fileStat.isSymbolicLink) {
		return {
			tooltip: localize('symbolicLlink', "Symbolic Link"),
			letter: '\u2937'
		};
	}
	if (fileStat.isUnknown) {
		return {
			tooltip: localize('unknown', "Unknown File Type"),
			letter: '?'
		};
	}
	if (fileStat.isExcluded) {
		return {
			color: listDeemphasizedForeground,
		};
	}

	return undefined;
}