Kotlin inline functions not reported as covered

[driessamyn]

Steps to reproduce

• JaCoCo version: 0.8.13.202504020838
• Operating system: macOS
• Tool integration: Gradle/Kotlin
• Complete executable reproducer: https://github.com/driessamyn/kotlin-coverage-bugs/tree/main
• Steps:
  1. Clone repo
  2. from repo root, run: ./gradlew jacocoTestReport

Expected behaviour

Code in example/src/main/kotlin/InlineFun.kt should be reorted as covered by the tests in example/src/test/kotlin/InlineExtensionFunTest.kt and example/src/test/kotlin/InlineFunTest.kt

Actual behaviour

JaCoCo reports 0% coverage

I tried this as an extension function and a "regular" function as I thought the issue may be related to it being an extension function, but both report 0% coverage.

I discovered this as part of moving Kapper to use JaCoCo as advised by the kover team.

As expected, the report is identical whether generated through Kover or JaCoCo directly.

[Godin]

@driessamyn the issue is related to inline functions whose only call site is in the tests, you can check this by calling from tests an intermediate non-inline function that is placed in main code next to your inline function

fun callsite(connection: Connection, block: Connection.() -> Unit) {
    notExtensionFunWithTransaction(connection, block)
}

inline fun notExtensionFunWithTransaction(connection: Connection, block: Connection.() -> Unit) {

please see #1873 (comment)

As described and shown in #1670 calculation of coverage for Kotlin inline functions requires analysis of call sites.
...
as of today Gradle plugin does not analyze test classes and so does not analyze call sites in test files.

We plan to improve this in Maven plugin - see #1689

And something similar has to be done in third-party integrations not developed by us such as Gradle plugin.

As well as in any other third-party integrations such as Kover (CC @qwwdfsad @shanshin @zuevmaxim).