Fix Issue 15888 - std.format should not produce deprecated hexstrings

[berni44]

No description provided.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	15888	normal	std.format should not produce deprecated hexstrings

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#7918"

[aG0aep6G]

Printing "\uXYZW" for a wchar 0xXYZW is not correct. "\u...." refers to a code point. A wchar is a code unit.

Example:

void main()
{
    import std.stdio;
    writeln(cast(wchar[]) [0xD83D, 0xDE08]); /* prints "😈" */
    writeln("\uD83D\uDE08"); /* Doesn't even compile. */
}

[aG0aep6G]

@thewilsonator, please don't merge this yet. And in general, please, please, please give others a chance to look at a PR before merging it.

[berni44]

Printing "\uXYZW" for a wchar 0xXYZW is not correct. "\u...." refers to a code point. A wchar is a code unit.

Example:

void main()
{
    import std.stdio;
    writeln(cast(wchar[]) [0xD83D, 0xDE08]); /* prints "😈" */
    writeln("\uD83D\uDE08"); /* Doesn't even compile. */
}

So what is it supposed to write? IMHO the examples you gave in the issue aren't valid either. (One is still a hexstring, while the other one doesn't compile...)

[aG0aep6G]

So what is it supposed to write? IMHO the examples you gave in the issue aren't valid either. (One is still a hexstring, while the other one doesn't compile...)

How about [cast(dchar) 0xFFFFFFF, cast(dchar) 0x42] or cast(dchar[]) [0xFFFFFFF, 0x42]? I'm not sure if there's a meaningful difference between the two.

Just throwing an exception could also be an option.

[berni44]

So what is it supposed to write? IMHO the examples you gave in the issue aren't valid either. (One is still a hexstring, while the other one doesn't compile...)

How about [cast(dchar) 0xFFFFFFF, cast(dchar) 0x42] or cast(dchar[]) [0xFFFFFFF, 0x42]? I'm not sure if there's a meaningful difference between the two.

Just throwing an exception could also be an option.

OK, let's try this one. Thanks for that idea and thanks for noting in time, that my first try was a bad idea...