Make conversions from char* to String explicit

[Ivorforce]

Describe the project you are working on

#11249 to optimize strings.

Also there's related #11257, with a similar proposal for StringName conversions in general.

Describe the problem or limitation you are having in your project

Strings are currently implicitly created from char *:

bool test(char *inp) {
	String s = inp;
	// rhs is implicitly converted to String before concatenation, leading to unnecessary allocation.
	String("b") + U"";
}

This is leading to many cases of implicit conversions to String for all of String's wide array of functions.

The main problem with allowing this instead of making conversions implicit is that it takes attention away from the programmer. I have previously described how this has specifically lead to 40k lines of shader code being parsed multiple times unnecessarily. If the conversion was explicit, it is more likely that conversion would only have happened once.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Make conversion from char* to String explicit:

explicit String(const char *p_str);

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Callers will have to adapt:

// Illegal
String s = "Test";
// Becomes
String s("Test");

// Illegal
register_string_name("Test")
// Becomes
register_string_name(String("Test"))

Macros and other convenience helperscshould probably be adjusted to accept string literals:

// D_METHOD should still support string literals.
ClassDB::bind_method(D_METHOD("poll"), &StreamPeerTLS::poll);

If this enhancement will not be used often, can it be worked around with a few lines of script?

Nope.

Is there a reason why this should be core and not an add-on in the asset library?

It's core.