SourceText collection & toString() for fns and methods

[Nikita-str]

This Pull Request closes #3780

In current approach all SourceText collected (because mostly a script consist of function codes and classes) and LinearSpan used to retrieve it when needed (to be fair toString() not often called); Gc::<SourceText> used for storage and therefore it can be deallocated only when we have access to no function from a source anymore.

It actually solve some tests from test262, but there is implementation for checking toString() correctness that take any [native code] as correct, without regard to whether it should accept in concrete case or not (assertToStringOrNativeFunction).

Also I don't sure about derive(arbitrary::Arbitrary) for core\ast\src\source.rs::Script & LinearSpan, just derive is ok here?

[codecov]

Codecov Report

Attention: Patch coverage is 78.97839% with 107 lines in your changes missing coverage. Please review.

Project coverage is 54.55%. Comparing base (6ddc2b4) to head (ce3e298).
Report is 359 commits behind head on main.

Files with missing lines	Patch %	Lines
core/parser/src/parser/statement/if_stm/mod.rs	0.00%	15 Missing ⚠️
core/engine/src/bytecompiler/mod.rs	54.83%	14 Missing ⚠️
core/engine/src/spanned_source_text.rs	58.62%	12 Missing ⚠️
core/ast/src/position.rs	80.39%	10 Missing ⚠️
core/ast/src/source_text.rs	73.91%	6 Missing ⚠️
core/parser/src/lexer/identifier.rs	16.66%	5 Missing ⚠️
.../statement/declaration/hoistable/class_decl/mod.rs	64.28%	5 Missing ⚠️
core/ast/src/source.rs	40.00%	3 Missing ⚠️
core/parser/src/lexer/mod.rs	93.61%	3 Missing ⚠️
core/parser/src/lexer/number.rs	66.66%	3 Missing ⚠️
... and 24 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4038      +/-   ##
==========================================
+ Coverage   47.24%   54.55%   +7.31%     
==========================================
  Files         476      490      +14     
  Lines       46892    49290    +2398     
==========================================
+ Hits        22154    26892    +4738     
+ Misses      24738    22398    -2340     

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[raskad]

I have not done an in depth review yet, just an initial question. As far as I see, the positions you used for the function start and end (LinearSpan and LinearPosition) only contain the start and end line of the function, correct?

I think that would not work in cases where other stuff is in the same line, e.g.:

let a = 1; function f() {return a + 1}; let b = 3;

In this case f.toString() should only be function f() {return a + 1} but it would return the complete line, right?

[Nikita-str]

@raskad
No, it contains linear position, in source code, not line. It is position(and span) in representation of source code as ~vector of code points.
so f.toString() will return function f() {return a + 1}.

in details:

let a = 1; function f() {return a + 1}; let b = 3;
//         ↑                         ↑ 
//     span.start                span.end

here is tests
and in particular it tests that:

        ia1 = (b) => b * 2    ;
        // \\ // \\ // \\ // \\ // \\ // \\ // \\
        A    =    ia1 . toString(    );

A will be exactly (b) => b * 2

[Nikita-str]

also you can read the issue where it was accepted to collect the source code(it should slow down parse stage performance)

[raskad]

Sorry for letting you wait so long for the full review. First of all thank you for the great contribution! Really nice work!

I added some specific comments, but I have one more general one. I would be in favor of Removing all the Options for the various SourceText fields. In principle, everytime we parse, compile and execute code, we must have the source text and a span. I did a quick check an I'm 99% sure the Options can be removed in all places.
In addition to the Script struct, the Module struct would also need the source text.
In some cases (e.g. the "dummy" use of the Bytecompiler for syntetic modules) there is really no source text, but there it is also never used. In those cases we can just use the default (empty vec).

Regarding Arbitrary, I think it should be a manual implementation that is just an empty source text. You can check here for en example of a manual impl:

boa/core/ast/src/expression/literal/mod.rs

Lines 121 to 137 in 517ad50

	#[cfg(feature = "arbitrary")]
	impl<'a> arbitrary::Arbitrary<'a> for Literal {
	fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
	let c = <u8 as arbitrary::Arbitrary<'a>>::arbitrary(u)? % 6;
	match c {
	0 => Ok(Self::String(<Sym as arbitrary::Arbitrary>::arbitrary(u)?)),
	1 => Ok(Self::Num(<f64 as arbitrary::Arbitrary>::arbitrary(u)?)),
	2 => Ok(Self::Int(<i32 as arbitrary::Arbitrary>::arbitrary(u)?)),
	3 => Ok(Self::BigInt(Box::new(
	<BigInt as arbitrary::Arbitrary>::arbitrary(u)?,
	))),
	4 => Ok(Self::Bool(<bool as arbitrary::Arbitrary>::arbitrary(u)?)),
	5 => Ok(Self::Null),
	_ => unreachable!(),
	}
	}
	}

[Nikita-str]

If remove Option<SourceText> from everywhere then I don't like what will happen with ByteCompiler::new / FunctionCompiler::new in no-source cases: we should have non-init marker, and create an empty Vec looks not safe enough. Option directly say that there is no object. But with Option we can forget to init it... I can add Option<SourceText> as fn new's arg and there will be no way to forget init.

[raskad]

If remove Option from everywhere then I don't like what will happen with ByteCompiler::new / FunctionCompiler::new in no-source cases: we should have non-init marker, and create an empty Vec looks not safe enough. Option directly say that there is no object. But with Option we can forget to init it... I can add Option as fn new's arg and there will be no way to forget init.

I was mostly concerned with the code in the bytecompiler being a bit easier to work with. Like you mentioned, with the Option and the set method you always have to remember it and do the whole if let check.
I don't see how the empty vec is unsafe, but what do you think about changing Gc<Inner> in SourceText to Option<Gc<Inner>>, or alternativeley, if you implement #4038 (comment), SpannedSourceText would be the only struct that is actually used outside of spanned_source_text.rs. That way you could also do the Option directly there.
If I'm not missing anything that should be a good solution, because we do not have the Options everywhere in the bytecompiler, the type is still the same size and in the case where we have no source, we do not allocate an empty Vec or a Gc.

[Nikita-str]

Seems like all done.
I also pass SourceText to the Module & then pass it from the Module to the ByteCompiler, but I don't test it.

---

We don't always have LinearSpan (for example here) so SpannedSourceText contains Option<LinearPosition>:

boa/core/engine/src/spanned_source_text.rs

Lines 44 to 48 in cbb2d79

	pub struct SpannedSourceText {
	source_text: SourceText,
	#[unsafe_ignore_trace]
	span: Option<LinearSpan>,
	}

In all other places Option is removed.

[raskad]

Looks really nice! Thank you for the work! Could you do a rebase, best would be after #4117 is merged, because the CI is broken without that.

One very minor nitpick: I would like to rename SourceText::new_pseudo to SourceText::new_empty and PSEUDO_LINEAR_SPAN to EMPTY_LINEAR_SPAN. I think it describes the values a bit better.

[raskad]

Thank you for the contribution. Great stuff. I'd be happy to merge this.

[jedel1043]

How much progress is this towards errors with backtraces? Haven't looked at it yet, I'm just curious if this would be another step forward or if we would have to essentially rewrite everything when we have nicer errors

[Nikita-str]

How much progress is this towards errors with backtraces?

Sorry, I actually don't sure what is needed for backtraced errors.
In this PR propagated only those linear spans that are needs for functions' toString.
LinearSpans are only needed when you need unchanged source code.
And I don't sure, do you need unchanged source code for backtraced errors at all?
If you need then at least it will be necessary to add LinearSpans to others AST nodes.
Otherwise it will be just parallel things, I suppose that you will not have to rewrite anything in any case.

[jedel1043]

If we just need to increasingly add LinearSpan to the rest of the AST nodes, that sounds perfect! And yeah, we need unchanged source code, because even after optimization passes we need to be able to reference the original line that a bytecode instruction comes from.

[jedel1043]

LGTM!