Add Scala Native Examples

[c0d33ngr]

This is a PR to close issue #3647

[c0d33ngr]

Hi @lihaoyi something like this or I have to use scalatags and mainargs?

[lihaoyi]

Let's use the same scalatags/mainargs example as we did in scalalib/basic/1-simple/.

You can get rid of most of the docs that are already part of scalalib/basic/1-simple/. The point of this page is to show what's unique about scala native, so the docs should highlight the differences and unique features of it: e.g. the compile to binary, the different optimization levels, etc.

[c0d33ngr]

Alright, it's noted

[c0d33ngr]

//build.mill
package build
import mill._, scalalib._, scalanativelib._

object `package` extends RootModule with ScalaNativeModule {
  def scalaVersion = "2.13.11"
  def scalaNativeVersion = "0.5.5"
  def nativeLinkingOptions = pathToWhereTheTargetWasSaved

  object test extends ScalaNativeTests {
    def ivyDeps = Agg(ivy"com.lihaoyi::utest:0.8.4")
    def testFramework = "utest.runner.Framework"
  }
}

#makefile
all : 
	gcc -m64 -shared -c native-src/HelloWorld.c -o target/libstub.so

@lihaoyi good day, I've some few questions to ask

Is it possible for me to run the commands in makefile from build.mill config?
Also how get the full file path of where am currently working in?

When I replace the def nativeLinkingOptions with the full path to the choice location to store the .so file, it worked. But before that I had to run make from terminal to generate the .so file in the location

That's why I asked whether it's possible to run the comments in makefile from build.mill

Lastly, is this what you want for the 2-interop code example?

[lihaoyi]

Is it possible for me to run the commands in makefile from build.mill config?

Sure, os.call(("make, "blah")). Though I suggest if you know what you want to call, you can os.call gcc directly rather than going through make

Also how get the full file path of where am currently working in?

T.dest or millSourcePath depending on what where am currently working in means

When I replace the def nativeLinkingOptions with the full path to the choice location to store the .so file, it worked. But before that I had to run make from terminal to generate the .so file in the location

Make an upstream task generate the SO file and return a PathRef for the downstream task to consume

Lastly, is this what you want for the 2-interop code example?

Yes the 2-interop example looks great. Perhaps let's make it return a value as well, so rather than printString we make it reverseString or something, just so people can see how that works? Other than that it looks great: a tiny C program, a tiny Scala facade, and a tiny Scala program all interacting. You just need to wire up gcc to compile the thing as part of Mill so we can avoid having to run make manually

[c0d33ngr]

@lihaoyi what you think

[lihaoyi]

Took another pass at reviewing this. I think we're getting there! There's still some changes necessary, but it's already in a much better state than it was before

[c0d33ngr]

@lihaoyi I've done the changes

[lihaoyi]

@lolgab could you take a pass at reviewing this? Since you have much more experience with scala native than I do

[lolgab]

Gave a quick look and found some possible improvements

[lolgab]

What is the point of this code?
it seems just scala code converted to C and also used after free. You can't use the CString after closing the Zone.
A better example would be using an open source html templating c library and then convert the C result to a Scala string

[lihaoyi]

It was meant to be a strawman hello-world Scala-Native application, so intentionally overly simple. Is it easy to integrate open source C libraries into scala native? I've never done it before

[lihaoyi]

Thanks @lolgab!

@c0d33ngr if we can just pass in the C sources via resources/scala-native, do we still need def nativeSources to reference them explicitly? Or would it suffice just to let scala-native pick them up from the resource path?

I think for the suggestion to add a third-party C library to use in the example, let's leave that to a follow-up bounty/PR, since it's a bit out of scope of the original ticket that was intentionally pretty minimal #3647

[c0d33ngr]

Thanks @lolgab!

@c0d33ngr if we can just pass in the C sources via resources/scala-native, do we still need def nativeSources to reference them explicitly? Or would it suffice just to let scala-native pick them up from the resource path?

I think for the suggestion to add a third-party C library to use in the example, let's leave that to a follow-up bounty/PR, since it's a bit out of scope of the original ticket that was intentionally pretty minimal #3647

@lolgab is so right!! As long as the C codes are in resources/scala-native, Scala Native will detect them so there's no need for compiling them within a task. I resolved most of the changes he suggested

[c0d33ngr]

Any more changes needed @lihaoyi ?

[lihaoyi]

One nit and then I think we're good, @c0d33ngr once you fix the merge conflicts and we get a green CI run I'll merge this and close out the bounty

[c0d33ngr]

One nit and then I think we're good, @c0d33ngr once you fix the merge conflicts and we get a green CI run I'll merge this and close out the bounty

Alright.. It's all greeny

At first, it wasn't but all of a sudden it restarted and ran successfully. Thought, the errors doesn't seem to be about scala-native examples

[lihaoyi]

@c0d33ngr just a flaky test, not related to your PR. Thanks again for your efforts!

Email me your international bank transfer details and I will close out the bounty

[sideeffffect]

Doesn't cResult escape here the Zone where it was allocated?

[c0d33ngr]

Alright... Noted

I'm into it

[c0d33ngr]

1-simple/src/Foo.scala

object Foo {
  
  def generateHtml(text: String) (using Zone) = {
    val html = "<h1>" + text + "</h1>\n"

    val cResult = toCString(html)
    cResult
  
  }

  @main
  def main(text: String) = Zone {
    stdio.printf(generateHtml(text))
  }
...

3-multi-module/foo/src/Foo.scala

...
object Foo {
  @main
  def main(@arg(name = "foo-text") fooText: String,
           @arg(name = "bar-text") barText: String): Unit = Zone {

    val cFooText = toCString(fooText)
    val cBarText = toCString(barText)

...

3-multi-module/bar/src/Bar.scala

...
object Bar {
  def main(args: Array[String]): Unit = Zone {
    println("Running HelloWorld function")
    val result = toCString(args(0))
    val barValue = HelloWorldBar.stringLength(result)
...

4-common-config/src/Foo.scala

...
object Foo {

  def generateHtml(text: String) (using Zone) = {
    val colored = Console.RED + "<h1>" + text + "</h1>" + Console.RESET

    val cResult = toCString(colored)
    cResult
  }
  
  def main(args: Array[String]): Unit = Zone {
    val value = generateHtml("hello")
    stdio.printf(c"Foo.value: %s\n", value)
  }
}

Hello @sideeffffect Here's is the updated code. Are they good to go?
Also please do a review on the scala-native codes I wrote just in case there are some changes needed to be made. It came to my notice that doc should be as good it can be cause future readers would depend on it

[lihaoyi]

@c0d33ngr please open a new PR with these changes, it's easier to discuss individual code changes on the PR, and when we're done we can just click the merge button :)

[c0d33ngr]

Alright..