Use of locale-sensitive methods with undefined locale may cause environment-sensitive bugs

[lionel-rowe]

Describe the bug

I've mentioned this before tangentially in a couple of issues (ex), but it's probably worth its own issue.

Use of locale-sensitive methods, such as toLocaleLowerCase, with an unspecified (undefined) locale may cause environment-sensitive bugs, because the default locale is host defined.

Steps to Reproduce

For example, in http/cookie.ts, which is marked browser-compatible:

std/http/cookie.ts

Line 361 in 6a4eb6c

switch (key.toLocaleLowerCase()) {

1. Open Firefox
2. Go to https://codepen.io/lionel-rowe/pen/rNEXmoG?editors=0010:

   import { getSetCookies } from 'https://esm.sh/jsr/@std/[email protected]/cookie'
   
   const setCookie = 'a=b; EXPIRES=Thu, 19 Sep 2024 07:47:28 GMT'
   const headers = new Headers({ 'set-cookie': setCookie })
   const cookie = getSetCookies(headers)[0]
                               
   document.querySelector('#target').textContent = JSON.stringify(cookie, null, 4)

3. Observe expected output (assuming your locale isn't Turkish):

   {
       "name": "a",
       "value": "b",
       "expires": "2024-09-19T07:47:28.000Z"
   }
   

4. Go to about:preferences
5. Set language to Turkish ("Türkçe"; Turkish for "language" is "dil" if you need to find the setting again)
6. Go back to or refresh https://codepen.io/lionel-rowe/pen/rNEXmoG?editors=0010 page
7. Observe output:

   {
       "name": "a",
       "value": "b",
       "unparsed": [
           "EXPIRES=Thu, 19 Sep 2024 07:47:28 GMT"
       ]
   }
   

Expected behavior

Consistent behavior in all locales

Environment

• OS: Windows 11
• deno version: N/A
• std version: @std/[email protected]

[lionel-rowe]

As far as I can see, the problematic uses are toLocaleLowerCase and toLocaleUpperCase in http/cookie.ts, http/_negotiation/encoding.ts, and in the various casing functions under text. By contrast, fmt/bytes.ts is a best practice for allowing opt-in locale sniffing:

std/fmt/bytes.ts

Lines 193 to 195 in 6a4eb6c

	* - If locale is a string, the value is expected to be a locale-key (for example: `de`).
	* - If locale is true, the system default locale is used for translation.
	* - If no value for locale is specified, the number is returned unmodified.

and testing it with minimal hard-coding:

std/fmt/bytes_test.ts

Lines 9 to 10 in 6a4eb6c

	const decimal = parts.find(({ type }) => type === "decimal")!.value;
	const group = parts.find(({ type }) => type === "group")!.value;

std/fmt/bytes_test.ts

Lines 75 to 82 in 6a4eb6c

	assertEquals(format(-0.4, { locale: true }), `-0${decimal}4 B`);
	assertEquals(format(0.4, { locale: true }), `0${decimal}4 B`);
	assertEquals(format(1001, { locale: true }), "1 kB");
	assertEquals(format(10.1, { locale: true }), `10${decimal}1 B`);
	assertEquals(
	format(1e30, { locale: true }),
	`1${group}000${group}000 YB`,
	);