Metadata cannot be extracted from fields and statics

[anissen]

I have the following sample (from http://haxe.org/manual/lf-metadata.html, slightly modified)

import haxe.rtti.Meta;

@author("Nicolas")
@debug
class MyClass {
    @author("Nicolas")
    @range(1, 8)
    var value:Int;

    @broken
    @:noCompletion
    static function method() { }
}

class Test {
    static public function main() {
        trace(Meta.getType(MyClass)); // { author : ["Nicolas"], debug : null }
        trace(Meta.getFields(MyClass)); // [1,8]
        trace(Meta.getStatics(MyClass)); // { broken: null }
    }
}

Compiling with Haxe to JavaScript and running with Node gives the following output:

{ author: [ 'Nicolas' ], debug: null }
{ value: { author: [ 'Nicolas' ], range: [ 1, 8 ] } }
{ method: { broken: null } }

Similarly, compiling with Haxe and running with Neko gives the following output:

Test.hx:17: { debug => null, author => [Nicolas] }
Test.hx:18: { value => { range => [1,8], author => [Nicolas] } }
Test.hx:19: { method => { broken => null } }

On try.haxe.org running the code (http://try.haxe.org/#8cFb8) gives the following output:

Object {author: Array[1], debug: null}
Object {}
Object {} 

That is, the result from Meta.getType(MyClass) is correct but the result from Meta.getFields(MyClass) and Meta.getStatics(MyClass) is incorrect.

[clemos]

It's weird, looks like a bug in the compiler ?
Try-haxe compiles with -dce full
but I can't reproduce locally...

[clemos]

Ok I've managed to reproduce, it's due to -dce full...

[clemos]

Best option would be to expose the dce flag in the GUI,
but it's not planned right now :S

[anissen]

A-ha, that's seems to be a clue! Compiling locally w. -dce full gives an empty result on both Neko and JavaScript.

I've updated the sample to use the previously unused fields:

import haxe.rtti.Meta;

@author("Nicolas")
@debug
class MyClass {
    @author("Nicolas")
    @range(1, 8)
    var value:Int;

    public function new(v) { value = v; }

    @broken
    @:noCompletion
    public static function method() { }
}

class Test {
    static public function main() {
        var c = new MyClass(42);
        MyClass.method();

        trace("Type");
        trace(Meta.getType(MyClass)); // { author : ["Nicolas"], debug : null }
        trace("Fields");
        trace(Meta.getFields(MyClass)); // [1,8]
        trace("Statics");
        trace(Meta.getStatics(MyClass)); // { broken: null }
    }
}

... and then the output is as expected:

It might be a "feature" rather than a "bug" but it's still pretty confusing. Maybe using haxe.rtti.Meta should an error/warning when fields are being removed due to dead code elimination. Or better yet; make the given fields not be removed by DCE - although that might be impossible to determine if reflection is involved...

[clemos]

In any case, it's an haxe compiler issue now ;)

[clemos]

Closing the issue, feel free to reopen if needed

[anissen]

Yeah, I agree that it's a compiler issue.

It might be nice to simply list the compiler flags somewhere on try.haxe for information. I could have reproduced the problem immediately in the haxe compiler if I had known that the -dce full flag was used.

Dunno, this instance might be a very edge-case-issue. Anyhow, thanks for your help :)