Reports contain invalid line="0" when using flatMapLatest() and combine() Kotlin coroutines functions about jacoco

[dzirbel]

I see, thanks for the response! For future reference, I think Kotlin/kotlinx.coroutines#3911 will be the main report going forward.

[Godin]

🎉 here is reproducer that doesn't require coroutines library

src/a/A.kt

package a;

@Suppress("UNUSED_PARAMETER")
public fun a0(p: suspend () -> Unit) {
}

public inline fun a(crossinline p: suspend () -> Unit) = a0 { p() }

src/b/B.kt

package b;

fun b() {
  a.a { }
}

their separate compilation

kotlin-compiler-1.9.10/bin/kotlinc -d classes src/a
kotlin-compiler-1.9.10/bin/kotlinc -d classes -cp classes src/b
find classes -name "*.class" -print0 | xargs -0 javap -v -p | grep "line 0"

leads to zero line numbers

        line 0: 3
        line 0: 44

[marchof]

Hi @dzirbel, thanks for the detailed bug report!

JaCoCo runs on Java classfiles and uses the contained debug information to extract line numbers. The line numbers are inserted by the respective compiler. It is a known issue that the Kotlin compiler sometimes emits line number 0. Please report this to the Kotlin project.

So why don't you see line number 0 in older versions? Because this was a bug in ASM (https://gitlab.ow2.org/asm/asm/-/issues/317989) which has been fixed.

[Godin]

For the record: some time ago I did bisection of changes in Kotlin compiler (see #1471 (comment)), which unfortunately revealed change in the coroutines library (JetBrains/kotlin@a1b04a7) and not in the compiler. Unfortunately wasn't able to craft reproducer that doesn't rely on coroutines library. And unfortunately did not managed to bisect changes in the coroutines library, because was unable to build its older versions due to massive rework of external dependencies and repositories.

CC @qwwdfsad

[Godin]

And to me seems that this is a compiler bug that was introduced during a switch to IR-based back-end:
support for crossinline suspend lambdas was added in Kotlin compiler version 1.4.0 - see JetBrains/kotlin@a1448eb
and for the above reproducer https://github.com/JetBrains/kotlin/releases/tag/v1.4-M1 produces zero line numbers only with -Xuse-ir option