dumper.js, why my emojis are escaped ?

[ysavary]

Hi all,

The yaml specification says (https://yaml.org/spec/1.2/spec.html#id2770814):

On output, a YAML processor must only produce acceptable characters. Any excluded characters must be presented using escape sequences. In addition, any allowed characters known to be non-printable should also be escaped. This isn’t mandatory since a full implementation would require extensive character property tables.

c-printable ::= #x9 | #xA | #xD | [#x20-#x7E]          /* 8 bit */
              | #x85 | [#xA0-#xD7FF] | [#xE000-#xFFFD] /* 16 bit */
              | [#x10000-#x10FFFF]                     /* 32 bit */

dumper.js follow the specification:

js-yaml/lib/js-yaml/dumper.js

Lines 186 to 191 in d8ba402

	function isPrintable(c) {
	return (0x00020 <= c && c <= 0x00007E)
	|| ((0x000A1 <= c && c <= 0x00D7FF) && c !== 0x2028 && c !== 0x2029)
	|| ((0x0E000 <= c && c <= 0x00FFFD) && c !== 0xFEFF /* BOM */)
	|| (0x10000 <= c && c <= 0x10FFFF);
	}

But the code that is calling isPrintable() use charCodeAt. This function will never return char > 0xFFFF so the supplementary planes range (0x010000 to 0x10FFFF) which include emojis will never be detected as printable.

js-yaml/lib/js-yaml/dumper.js

Lines 289 to 293 in d8ba402

	for (i = 0; i < string.length; i++) {
	char = string.charCodeAt(i);
	if (!isPrintable(char)) {
	return STYLE_DOUBLE;
	}

I tested with codePointAt and Array.from(string) to iterate the chars while managing surrogate pairs: emojis are not escaped as desired.