Generate bindings for defines for variables

[kornilova203]

During DefineFinderAction save all defines that use an identifier.
During AST traversal find variables declarations and check if there is a define for the variable.
If such define exist then save it in a vector field in IR and generate Scala code for it:

extern int a;
#define A a

  @name("a")
  def A: native.CInt = native.extern

[kornilova203]

Closes #4

[jonas]

I'd expect this be a var since it is not extern const int a?

[kornilova203]

Thanks! Yes, it at least should be val
I tried to replace it with var and change value of A but got compiler error
It is not informative:

[error] scala.scalanative.util.UnsupportedException: List(10) (class scala.collection.immutable.$colon$colon)
[error] 	at scala.scalanative.util.package$.unsupported(package.scala:17)
[error] 	at scala.scalanative.nscplugin.NirGenExpr$ExprBuffer.genApplyExternAccessor(NirGenExpr.scala:1572)
[error] 	at scala.scalanative.nscplugin.NirGenExpr$ExprBuffer.genApplyMethod(NirGenExpr.scala:1556)
...

I suppose it is related to this issue scala-native/scala-native#202

So I'll change it to val

[jonas]

Interesting. /me flushing down getopt.h as candidate for #59. 😭

I took a quick look at https://github.com/sjrd/scala-js-ts-importer/blob/master/samples/modifiers.d.ts.scala as inspiration on how to translate variables and it uses val for const and def for readonly members. @sjrd if you have time maybe you can enlighten us on the choices made for the Typescript importer.

In the standard Scala Native bindings, I see def stdin, not sure if this is because it calls a method.

[sjrd]

The difference between val and def is that val is stable, i.e., is guaranteed to always return the same value for the same receiver. def can return different values as time passes. This corresponds to const versus readonly.

[kornilova203]

Okay, then it would be better to have val for const values and def for all other

[jonas]

I agree. Thanks for your input @sjrd !

[jonas]

Why is there no variable generated for f?

[kornilova203]

Because this commit is about defines
Define for f is private __PRIVATE and therefore filtered

[jonas]

When we will add support for extern int c (#70 this will still generate a def c: native.CInt = extern, right?

[kornilova203]

Yes

[jonas]

When we will support extern variables this could be simply:

def a: native.CInt = extern
def A = a

WDYT?

[kornilova203]

Yes, but if a variable is private then it will be filtered, so we should be careful here

extern int __private_int;
#define my_int __private_int

[jonas]

🎉

[jonas]

This will need to be changed to support extern variables. Ideally everything related with macros/defines would live in possibleVarDefines so we'd end up with:

class Variable : public TypeAndName {
  // ...
}

class VarDefine : public Define {
  // ...
  private:
    std::string defineName; // name of the alias
    std::string variableName; // name of the aliased variable
}

[kornilova203]

Variable with def gives this error when I am trying to get it's value:

[error] java.lang.NullPointerException
[error] 	at sbt.JUnitXmlTestsListener$TestSuite.$anonfun$stop$2(JUnitXmlTestsListener.scala:92)
[error] 	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
[error] 	at scala.collection.immutable.List.foreach(List.scala:389)
...

extern int a;

Binding:

@name("a")
def A: native.CInt = native.extern

Test:

assert(VarDefine.A == 23)

Test succeeds if def is changed to val 😕

[jonas]

I suspect that def is translated into a method call which blows up because the symbol is not a method. Looks like we have to use val then.

[jonas]

BTW, it would be good to also update the limitation notice in the README.