[Proposal] Make toLowerCase and toUpperCase based on Locale.ROOT by default

[Xuelei Fan]

Just curious, this is a known issue for many years, how those areas like Turkish survive?  Is there a workaround for those areas or the use of the methods is not common any longer?

Xuelei 

> On Jan 26, 2023, at 4:35 AM, Glavo <zjx001202 at gmail.com> wrote:
> 
> At present, the no-parameter toLowerCase and toUpperCase methods of String are based on the default locale.
> 
> I checked all the uses of this method in OpenJDK, and found that most of the use cases are suspicious, and even there are some hidden bugs.
> For example, I just found that jdk.incubator.vector.LaneType will trigger assertion failure on Turkish locale, and opened a PR for this problem:
> 
> https://github.com/openjdk/panama-vector/pull/210
> 
> In addition to such obvious problems, some use cases behave suspiciously after calling Locale.setDefault.
> I am investigating these problems and preparing to open a PR to solve these hidden bugs.
> 
> In all the third-party libraries I have used, I have never seen the correct use of these two methods.
> Although the behavior of modifying API methods is destructive, I think it is worthwhile to consider whether to modify its behavior for such a suspicious method.
> If users need locale-sensitive case conversion, it may be better to explicitly use Locale.getDefault().
> Using Locale.ROOT as the default value also helps to keep the behavior of these two methods consistent with equalsIgnoreCase, Character.toLowerCase/toUpperCase and other methods.
> 
> This is my rough idea. I hope to get your suggestions.

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