Literal: Remove null and boolean parsers

[Acconut]

Addresses #93.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[coveralls]

Coverage decreased (-0.1%) to 93.4% when pulling 02f0009 on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[Hywan]

You should move these tests where constants are used, so in qualified_name.

[Acconut]

Should all of these tests be moved? I am not sure if they are just redundant then, in particular since a test for unqualified names already exists:

parser/source/rules/tokens.rs

Lines 242 to 248 in ff0ca1f

	#[test]
	fn case_unqualified_name() {
	let input = Span::new(b"Foo");
	let output = Result::Done(Span::new_at(b"", 3, 1, 4), Name::Unqualified(input));
	assert_eq!(qualified_name(input), output);
	}

[Hywan]

I guess it's better to ensure that special constants are correctly parsed ;-). So I prefer to keep them.

[Acconut]

@Hywan Do you have an idea why suddenly the tests for Rust 1.14 failed? https://travis-ci.org/tagua-vm/parser/jobs/234969027

[Hywan]

A dependency is breaking our build. Continue, I will fix it on my end.

[Acconut]

@Hywan Did you seen my response to your comment on the code? #104 (comment) :)

[Hywan]

@Acconut Done.

[coveralls]

Coverage decreased (-0.08%) to 93.426% when pulling e7acb9b on Acconut:remove_null_boolean_parser into e7aa963 on tagua-vm:master.

[Acconut]

Added back the tests.

[Hywan]

Is it ready for a review?

[Acconut]

Yes, indeed :)

[Hywan]

I have a bad news for you. Yes, according to the grammar, true, false, and null are not constants but qualified names. Yes, we should remove these parsers. But, I just remembered these tweets, https://twitter.com/hoaproject/status/688991362151280640 and https://twitter.com/hoaproject/status/689459255485698049. Quoting (and simplifying):

@hoaproject: https://3v4l.org/Lttus is it a regression?
@nikic: No, it's an intentional change. true/false/null are always off-limits now, while previously only sometimes.
@hoaproject: Why are they off-limit now :-)?
@nikic: Because they are really language items that happen to be implemented through constants. It should not be possible to overload em

So, as far as I understand, they are qualified names with special treatements. Thus, my conclusion would be to keep them right now, and see if it raises some errors in existing test suites from Zend or HHVM.

What do you think?

I am sorry it comes to my mind riht now after all your work. Maybe an input from @nikic or @jubianchi would confirm.

[Acconut]

That's interesting, I wasn't aware of this fact. And you don't have to apologize, it's better to think of this now than later :)

Another option, I could think of is treat them similar to how magic constants, such as LINE may be implemented (see http://php.net/manual/en/language.constants.predefined.php). They could be parsed as qualified names but have a special treatment.

[nikic]

@Hywan Haven't followed the context here, but please note that while true, false and null are excluded from the namespace fallback, they still generally participate in name resolution. For example writing use const false as true; is valid and will make true resolve to false.

[Hywan]

Thanks!