Steps to reproduce

• JaCoCo version: 0.8.14 (shown in bottom-right corner of JaCoCo HTML report)
• Operating system: macOS 15.3
• Tool integration: Gradle 8.12 (bug is in JaCoCo bytecode analysis, not Gradle-specific — reproduced via ./gradlew test jacocoTestReport)
• Complete executable reproducer: https://github.com/psancheti6666/jacoco-jvmstatic-interface-bug
• Steps:
  • gradle wrapper --gradle-version 8.12
  • ./gradlew test jacocoTestReport
  • Open build/reports/jacoco/test/html/index.html → navigate to com.example.coverage → IConfig

Additional environment info:

• Kotlin: 2.1.20
• JDK: OpenJDK 17

Expected behaviour

IConfig.forUser should be reported as covered. All 4 tests pass and directly invoke IConfig.forUser(...). The method body is fully executed during the test run.

Actual behaviour

JaCoCo reports IConfig.forUser as 0% covered (1 missed instruction, 1 missed line, 1 missed method) despite all 4 tests passing.

The missed line is the closing } of the method (line 47 in IConfig.kt). Lines 43–46 (the function declaration and return statement) have no coverage entry under IConfig.class — they appear only under IConfig$Companion.class where they are correctly shown as fully covered.

Source: IConfig.kt

interface IConfig {
    fun getBaseUrl(): String
    fun processUrl(url: String): String

    companion object {
        @JvmStatic
        fun forUser(isConsumer: Boolean): IConfig {            // line 43 — no entry in IConfig.class
            return ConfigProvider(                             // line 44 — no entry in IConfig.class
                enterpriseProvider = { EnterpriseConfig() },
                consumerProvider   = { ConsumerConfig() }
            ).provideFor(isConsumer)
        }                                                      // line 47 — mi="1" ci="0" (false miss)
    }
}

Test call sites (all Kotlin — 4 tests, all pass)

val config = IConfig.forUser(isConsumer = false)  // resolves to IConfig$Companion.forUser(...)
val config = IConfig.forUser(isConsumer = true)   // resolves to IConfig$Companion.forUser(...)

XML output — IConfig.class entry (the bridge — 0% covered)

<class name="com/example/coverage/IConfig" sourcefilename="IConfig.kt">
  <method name="forUser" desc="(Z)Lcom/example/coverage/IConfig;" line="47">
    <counter type="INSTRUCTION" missed="1" covered="0"/>
    <counter type="LINE"        missed="1" covered="0"/>
    <counter type="COMPLEXITY"  missed="1" covered="0"/>
    <counter type="METHOD"      missed="1" covered="0"/>
  </method>
</class>

XML output — IConfig$Companion.class entry (real implementation — fully covered)

<class name="com/example/coverage/IConfig$Companion" sourcefilename="IConfig.kt">
  <method name="forUser" desc="(Z)Lcom/example/coverage/IConfig;" line="43">
    <counter type="INSTRUCTION" missed="0" covered="8"/>
    <counter type="METHOD"      missed="0" covered="1"/>
  </method>
</class>

XML output — sourcefile entry for IConfig.kt

<sourcefile name="IConfig.kt">
  <line nr="43" mi="0" ci="6" mb="0" cb="0"/>
  <line nr="44" mi="0" ci="5" mb="0" cb="0"/>
  <line nr="45" mi="0" ci="5" mb="0" cb="0"/>
  <line nr="46" mi="0" ci="2" mb="0" cb="0"/>
  <line nr="47" mi="1" ci="0" mb="0" cb="0"/>
</sourcefile>

javap output for the bridge method on IConfig.class

public static com.example.coverage.IConfig forUser(boolean);
  descriptor: (Z)Lcom/example/coverage/IConfig;
  flags: (0x0009) ACC_PUBLIC, ACC_STATIC
  Code:
    stack=2, locals=1, args_size=1
       0: getstatic     #16   // Field Companion:Lcom/example/coverage/IConfig$Companion;
       3: iload_0
       4: invokevirtual #20   // Method IConfig$Companion.forUser:(Z)Lcom/example/coverage/IConfig;
       7: areturn
    LineNumberTable:
      line 47: 7

The LineNumberTable has a single entry: line 47: 7. Only the areturn at offset 7 carries a line number (the closing brace). Offsets 0, 3, and 4 have no line number entry and are not counted in the line coverage data.

Root cause

When Kotlin compiles @JvmStatic inside an interface companion object, it generates two class files:

1. IConfig$Companion.class — the actual method body (fully covered by tests).
2. IConfig.class — a synthetic static bridge for Java interop: return Companion.forUser(isConsumer).

A Kotlin call site (IConfig.forUser(...)) is resolved by the compiler directly to IConfig$Companion.forUser(...), bypassing the bridge. Only a Java call site goes through it. All tests are Kotlin, so the bridge's areturn instruction (mapped to line 47) is never executed.

Relation to existing issues

The specific combination: @JvmStatic + companion object + interface (not class) + Kotlin-only callers.