@Preview composable excluded only when not wrapped in themed @Composable

[Gh0stahCZ]

Custom exclusion annotation works for a plain @Preview but fails when the preview wraps content in an annotated theme function.

Reproducer: fresh clone of repo https://github.com/jacoco/example-jacoco-kotlin-compose Command: ./gradlew clean test jacocoTestReport

Snippet:

@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.FUNCTION, AnnotationTarget.CLASS)
annotation class ExcludeFromJacocoGeneratedReport

package org.example

import androidx.compose.desktop.ui.tooling.preview.Preview
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.runtime.*

@Composable
fun example() {
    var counter by remember { mutableStateOf(0) }
    if (counter == 2) {
        return
    }
    Button(onClick = { counter++ }) {
        if (counter == 0) {
            Text("Click me")
        } else {
            Text("Click me again")
        }
    }

}

@Composable
@ExcludeFromJacocoGeneratedReport
fun DummyTheme(content: @Composable () -> Unit) {
    content()
}


@Preview
@Composable
@ExcludeFromJacocoGeneratedReport
fun NoThemePreview() {
    example()
}

@Preview
@Composable
@ExcludeFromJacocoGeneratedReport
fun ThemedPreview() {
    DummyTheme @ExcludeFromJacocoGeneratedReport {
        example()
    }
}

Expected: Both previews fully excluded.
Actual: NoThemePreview excluded, ThemedPreview counted (lines attributed to generated synthetic methods).

Question:

1. Is this an expected limitation of how the Compose compiler rewrites @Composable / @Preview functions?
2. What is the recommended JaCoCo filter (class/method name patterns or annotations) to exclude every @Preview function and any helper lambdas they generate?

===========

Generated jacocoTestReport.xml:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE report PUBLIC "-//JACOCO//DTD Report 1.1//EN" "report.dtd">
<report name="example-jacoco-kotlin-compose">
    <sessioninfo id="Tomass-MacBook-Pro-3.local-6e2358ea" start="1760083990908" dump="1760083992584"/>
    <package name="org/example">
        <class name="org/example/ExampleKt" sourcefilename="Example.kt">
            <method name="example" desc="(Landroidx/compose/runtime/Composer;I)V" line="9">
                <counter type="INSTRUCTION" missed="0" covered="74"/>
                <counter type="BRANCH" missed="0" covered="2"/>
                <counter type="LINE" missed="0" covered="6"/>
                <counter type="COMPLEXITY" missed="0" covered="2"/>
                <counter type="METHOD" missed="0" covered="1"/>
            </method>
            <method name="example$lambda$1" desc="(Landroidx/compose/runtime/MutableState;)I" line="10">
                <counter type="INSTRUCTION" missed="0" covered="10"/>
                <counter type="LINE" missed="0" covered="1"/>
                <counter type="COMPLEXITY" missed="0" covered="1"/>
                <counter type="METHOD" missed="0" covered="1"/>
            </method>
            <method name="example$lambda$2" desc="(Landroidx/compose/runtime/MutableState;I)V" line="10">
                <counter type="INSTRUCTION" missed="0" covered="12"/>
                <counter type="LINE" missed="0" covered="1"/>
                <counter type="COMPLEXITY" missed="0" covered="1"/>
                <counter type="METHOD" missed="0" covered="1"/>
            </method>
            <method name="example$lambda$4$0" desc="(Landroidx/compose/runtime/MutableState;)Lkotlin/Unit;" line="14">
                <counter type="INSTRUCTION" missed="0" covered="10"/>
                <counter type="LINE" missed="0" covered="1"/>
                <counter type="COMPLEXITY" missed="0" covered="1"/>
                <counter type="METHOD" missed="0" covered="1"/>
            </method>
            <method name="example$lambda$5" desc="(Landroidx/compose/runtime/MutableState;Landroidx/compose/foundation/layout/RowScope;Landroidx/compose/runtime/Composer;I)Lkotlin/Unit;" line="15">
                <counter type="INSTRUCTION" missed="0" covered="67"/>
                <counter type="BRANCH" missed="0" covered="2"/>
                <counter type="LINE" missed="0" covered="5"/>
                <counter type="COMPLEXITY" missed="0" covered="2"/>
                <counter type="METHOD" missed="0" covered="1"/>
            </method>
            <counter type="INSTRUCTION" missed="0" covered="173"/>
            <counter type="BRANCH" missed="0" covered="4"/>
            <counter type="LINE" missed="0" covered="11"/>
            <counter type="COMPLEXITY" missed="0" covered="7"/>
            <counter type="METHOD" missed="0" covered="5"/>
            <counter type="CLASS" missed="0" covered="1"/>
        </class>
        <class name="org/example/ComposableSingletons$ExampleKt$lambda$-545336751$1" sourcefilename="Example.kt"/>
        <class name="org/example/ExcludeFromJacocoGeneratedReport" sourcefilename="ExcludeFromJacocoGeneratedReport.kt"/>
        <class name="org/example/ComposableSingletons$ExampleKt" sourcefilename="Example.kt">
            <method name="&lt;clinit&gt;" desc="()V" line="42">
                <counter type="INSTRUCTION" missed="7" covered="0"/>
                <counter type="LINE" missed="1" covered="0"/>
                <counter type="COMPLEXITY" missed="1" covered="0"/>
                <counter type="METHOD" missed="1" covered="0"/>
            </method>
            <counter type="INSTRUCTION" missed="7" covered="0"/>
            <counter type="LINE" missed="1" covered="0"/>
            <counter type="COMPLEXITY" missed="1" covered="0"/>
            <counter type="METHOD" missed="1" covered="0"/>
            <counter type="CLASS" missed="1" covered="0"/>
        </class>
        <sourcefile name="Example.kt">
            <line nr="9" mi="0" ci="4" mb="0" cb="0"/>
            <line nr="10" mi="0" ci="41" mb="0" cb="0"/>
            <line nr="11" mi="0" ci="5" mb="0" cb="2"/>
            <line nr="12" mi="0" ci="4" mb="0" cb="0"/>
            <line nr="14" mi="0" ci="45" mb="0" cb="0"/>
            <line nr="15" mi="0" ci="12" mb="0" cb="2"/>
            <line nr="16" mi="0" ci="22" mb="0" cb="0"/>
            <line nr="17" mi="0" ci="9" mb="0" cb="0"/>
            <line nr="18" mi="0" ci="22" mb="0" cb="0"/>
            <line nr="20" mi="0" ci="2" mb="0" cb="0"/>
            <line nr="22" mi="0" ci="7" mb="0" cb="0"/>
            <line nr="42" mi="7" ci="0" mb="0" cb="0"/>
            <counter type="INSTRUCTION" missed="7" covered="173"/>
            <counter type="BRANCH" missed="0" covered="4"/>
            <counter type="LINE" missed="1" covered="11"/>
            <counter type="COMPLEXITY" missed="1" covered="7"/>
            <counter type="METHOD" missed="1" covered="5"/>
            <counter type="CLASS" missed="1" covered="1"/>
        </sourcefile>
        <sourcefile name="ExcludeFromJacocoGeneratedReport.kt"/>
        <counter type="INSTRUCTION" missed="7" covered="173"/>
        <counter type="BRANCH" missed="0" covered="4"/>
        <counter type="LINE" missed="1" covered="11"/>
        <counter type="COMPLEXITY" missed="1" covered="7"/>
        <counter type="METHOD" missed="1" covered="5"/>
        <counter type="CLASS" missed="1" covered="1"/>
    </package>
    <counter type="INSTRUCTION" missed="7" covered="173"/>
    <counter type="BRANCH" missed="0" covered="4"/>
    <counter type="LINE" missed="1" covered="11"/>
    <counter type="COMPLEXITY" missed="1" covered="7"/>
    <counter type="METHOD" missed="1" covered="5"/>
    <counter type="CLASS" missed="1" covered="1"/>
</report>```