`Found a dangling UndefinedParam` on Scala.js

[armanbilge]

[error] /home/runner/work/observe/observe/modules/web/client/src/main/scala/observe/web/client/handlers/WebSocketHandler.scala:40:7: Found a dangling UndefinedParam at Position(https://raw.githubusercontent.com/gemini-hlsw/observe/4c95fb1dd6e860604d1446f05b30eab0165f6d22/modules/web/client/src/main/scala/observe/web/client/handlers/WebSocketHandler.scala,104,52). This is likely due to a bad interaction between a macro or a compiler plugin and the Scala.js compiler plugin. If you hit this, please let us know.

https://github.com/gemini-hlsw/observe/runs/5059573540?check_suite_focus=true#step:7:402

Thanks for the encouraging message to open an issue! :)

[armanbilge]

Alas, I have run into this again in another project buntec/scala-js-snabbdom#34 (comment)

[ckipp01]

If you hit this, please let us know.
Thanks for the encouraging message to open an issue! :)

Thanks for the report! I actually think this is emitted from ScalaJS, not scoverage. I have no idea just glancing at this, to be honest I'm not sure what a dangling UndefinedParam is.

[armanbilge]

See #196 for a similar issue, which was closed by #281. So probably this needs a similar sort of fix.

[armanbilge]

Ok, I isolated it one problematic line.

https://github.com/buntec/scala-js-snabbdom/blob/f1a3f58b934e739cce72157f01aaed1ac7d0eeac/snabbdom/src/main/scala/snabbdom/modules/Styles.scala#L88

elm.asInstanceOf[dom.HTMLElement].style.setProperty(name, cur)

Where HTMLElement comes from https://github.com/scala-js/scala-js-dom/

[armanbilge]

Isolated down to the setProperty call, which is defined here:
https://github.com/scala-js/scala-js-dom/blob/883d3d944e5a6909551dfe256681b22eb8b33f93/dom/src/main/scala/org/scalajs/dom/CSSStyleDeclaration.scala#L183

I reckon it's the default parameter again, just like was supposedly solved by #281. Maybe another case?

[armanbilge]

Oh hang on, maybe it's a regression. The test is being ignored!

scalac-scoverage-plugin/plugin/src/test/scala/scoverage/PluginCoverageScalaJsTest.scala

Line 9 in 1d404ca

test("scoverage should ignore default undefined parameter".ignore) {

[armanbilge]

Became ignored when dropping 2.11 in 5d3c897, idk why though.

[armanbilge]

I used a workaround in buntec/scala-js-snabbdom#34 to get coverage working with JSDOM, which is cool. But would be great to re-enable this test and fix the regression!

[ckipp01]

I used a workaround in buntec/scala-js-snabbdom#34 to get coverage working with JSDOM, which is cool. But would be great to re-enable this test and fix the regression!

I'm glad you found a workaround :). I'll be pretty honest, I'm a bit hands off with scoverage at the moment, and don't intend on putting much time into it, just enough to keep it alive and published, so I probably won't be diving into this. However, if anyone is interested in contributing, I'm more than happy to review.

[armanbilge]

@ckipp01 yeah, no worries 😁

I have half a mind to dig into this, but what would be very helpful is a pointer how to run the scoverage compiler in the test suite with Scala.js and the Scala.js stdlib on its classpath. Nevermind, I've figured this out :)

It's not really obvious to me how the test was accomplishing that before. Thanks!

scalac-scoverage-plugin/plugin/src/test/scala/scoverage/PluginCoverageScalaJsTest.scala

Lines 7 to 19 in 1d404ca

	class PluginCoverageScalaJsTest extends FunSuite with MacroSupport {
	test("scoverage should ignore default undefined parameter".ignore) {
	val compiler = ScoverageCompiler.default
	compiler.compileCodeSnippet(
	"""import scala.scalajs.js
	|
	|object JSONHelper {
	| def toJson(value: String): String = js.JSON.stringify(value)
	|}""".stripMargin
	)
	assert(!compiler.reporter.hasErrors)
	compiler.assertNMeasuredStatements(4)