Plugin behaves abnormally when add is called in a function

Hi there! If I call add in a function with return value the plugin fails to evaluate the project. I created you a sample project here

exampleKSP (1).zip

My env:

------------------------------------------------------------
Gradle 9.1.0
------------------------------------------------------------

Build time:    2025-09-18 13:05:56 UTC
Revision:      e45a8dbf2470c2e2474ccc25be9f49331406a07e

Kotlin:        2.2.0
Groovy:        4.0.28
Ant:           Apache Ant(TM) version 1.10.15 compiled on August 25 2024
Launcher JVM:  24.0.2 (Arch Linux 24.0.2)
Daemon JVM:    /usr/lib/jvm/java-24-openjdk (no JDK specified, using current Java home)
OS:            Linux 6.6.103-3-MANJARO amd64

Build file:

plugins {
    application
    kotlin("jvm") version "2.2.20"
    kotlin("plugin.dataframe") version "2.2.20"
}

group = "net.mattbaumann"
version = "1.0-SNAPSHOT"

application {
    mainClass = "MainKt"
}

repositories {
    mavenCentral()
}

dependencies {
    implementation(kotlin("reflect"))
    implementation(kotlin("stdlib"))
    implementation("org.jetbrains.kotlinx:dataframe:1.0.0-Beta3")

    testImplementation(kotlin("test"))
}

tasks.test {
    useJUnitPlatform()
}

kotlin {
    jvmToolchain(24)
}

Faulty example code

fun main(args: Array<String>) {
    val iso = test()
    println("columns ${iso.columnsCount()} rows ${iso.rowsCount()}")
}

fun test() : DataFrame<Iso6393Raw> {
    val iso3url = URI("https://iso639-3.sil.org/sites/iso639-3/files/downloads/iso-639-3.tab").toURL()
    return DataFrame.readTsv(iso3url).cast<Iso6393Raw>().add {  }
}

@DataSchema
@Suppress("unused")
interface Iso6393Raw { }

I get the following exception:

> Task :compileKotlin FAILED
e: org.jetbrains.kotlin.util.FileAnalysisException: While analysing /home/matt/IdeaProjects/exampleKSP/src/main/kotlin/Main.kt:16:5: org.jetbrains.kotlin.utils.exceptions.KotlinIllegalArgumentExceptionWithAttachments: Exception in expression checkers
        at org.jetbrains.kotlin.util.AnalysisExceptionsKt.wrapIntoFileAnalysisExceptionIfNeeded(AnalysisExceptions.kt:57)
        at org.jetbrains.kotlin.fir.FirCliExceptionHandler.handleExceptionOnFileAnalysis(Utils.kt:267)
        at org.jetbrains.kotlin.fir.pipeline.AnalyseKt.runCheckers(analyse.kt:68)
        at org.jetbrains.kotlin.fir.pipeline.FirUtilsKt.resolveAndCheckFir(firUtils.kt:77)
        at org.jetbrains.kotlin.cli.pipeline.jvm.JvmFrontendPipelinePhase.executePhase(JvmFrontendPipelinePhase.kt:165)
        at org.jetbrains.kotlin.cli.pipeline.jvm.JvmFrontendPipelinePhase.executePhase(JvmFrontendPipelinePhase.kt:47)
        at org.jetbrains.kotlin.cli.pipeline.PipelinePhase.phaseBody(PipelinePhase.kt:68)
        at org.jetbrains.kotlin.cli.pipeline.PipelinePhase.phaseBody(PipelinePhase.kt:58)
        at org.jetbrains.kotlin.config.phaser.NamedCompilerPhase.invoke(CompilerPhase.kt:102)
        at org.jetbrains.kotlin.backend.common.phaser.CompositePhase.invoke(PhaseBuilders.kt:22)
        at org.jetbrains.kotlin.config.phaser.CompilerPhaseKt.invokeToplevel(CompilerPhase.kt:53)
        at org.jetbrains.kotlin.cli.pipeline.AbstractCliPipeline.runPhasedPipeline(AbstractCliPipeline.kt:109)
        at org.jetbrains.kotlin.cli.pipeline.AbstractCliPipeline.execute(AbstractCliPipeline.kt:68)
        at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecutePhased(K2JVMCompiler.kt:79)
        at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecutePhased(K2JVMCompiler.kt:45)
        at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.kt:90)
        at org.jetbrains.kotlin.cli.common.CLICompiler.exec(CLICompiler.kt:352)
        at org.jetbrains.kotlin.daemon.CompileServiceImpl.compile(CompileServiceImpl.kt:1706)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
        at java.base/java.lang.reflect.Method.invoke(Method.java:565)
        at java.rmi/sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:351)
        at java.rmi/sun.rmi.transport.Transport.serviceCall(Transport.java:166)
        at java.rmi/sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:543)
        at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:744)
        at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:623)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1095)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:619)
        at java.base/java.lang.Thread.run(Thread.java:1447)
Caused by: org.jetbrains.kotlin.utils.exceptions.KotlinIllegalArgumentExceptionWithAttachments: Exception in expression checkers
        at org.jetbrains.kotlin.fir.analysis.checkers.expression.ExpressionCheckersDiagnosticComponent.visitReturnExpression(ExpressionCheckersDiagnosticComponent.kt:544)
        at org.jetbrains.kotlin.fir.analysis.checkers.expression.ExpressionCheckersDiagnosticComponent.visitReturnExpression(ExpressionCheckersDiagnosticComponent.kt:25)
        at org.jetbrains.kotlin.fir.expressions.FirReturnExpression.accept(FirReturnExpression.kt:31)
        at org.jetbrains.kotlin.fir.analysis.collectors.CheckerRunningDiagnosticCollectorVisitor.checkElement(CheckerRunningDiagnosticCollectorVisitor.kt:24)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitAnnotationContainer(AbstractDiagnosticCollectorVisitor.kt:66)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitAnnotationContainer(AbstractDiagnosticCollectorVisitor.kt:36)
        at org.jetbrains.kotlin.fir.visitors.FirDefaultVisitor.visitStatement(FirDefaultVisitor.kt:30)
        at org.jetbrains.kotlin.fir.visitors.FirDefaultVisitor.visitExpression(FirDefaultVisitor.kt:33)
        at org.jetbrains.kotlin.fir.visitors.FirDefaultVisitor.visitJump(FirDefaultVisitor.kt:51)
        at org.jetbrains.kotlin.fir.visitors.FirDefaultVisitor.visitReturnExpression(FirDefaultVisitor.kt:63)
        at org.jetbrains.kotlin.fir.expressions.FirReturnExpression.accept(FirReturnExpression.kt:31)
        at org.jetbrains.kotlin.fir.expressions.impl.FirBlockImpl.acceptChildren(FirBlockImpl.kt:37)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitNestedElements(AbstractDiagnosticCollectorVisitor.kt:44)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitAnnotationContainer(AbstractDiagnosticCollectorVisitor.kt:67)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitAnnotationContainer(AbstractDiagnosticCollectorVisitor.kt:36)
        at org.jetbrains.kotlin.fir.visitors.FirDefaultVisitor.visitStatement(FirDefaultVisitor.kt:30)
        at org.jetbrains.kotlin.fir.visitors.FirDefaultVisitor.visitExpression(FirDefaultVisitor.kt:33)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitBlock(AbstractDiagnosticCollectorVisitor.kt:212)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitBlock(AbstractDiagnosticCollectorVisitor.kt:36)
        at org.jetbrains.kotlin.fir.expressions.FirBlock.accept(FirBlock.kt:29)
        at org.jetbrains.kotlin.fir.declarations.impl.FirSimpleFunctionImpl.acceptChildren(FirSimpleFunctionImpl.kt:70)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitNestedElements(AbstractDiagnosticCollectorVisitor.kt:44)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitSimpleFunction(AbstractDiagnosticCollectorVisitor.kt:820)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitSimpleFunction(AbstractDiagnosticCollectorVisitor.kt:36)
        at org.jetbrains.kotlin.fir.declarations.FirSimpleFunction.accept(FirSimpleFunction.kt:51)
        at org.jetbrains.kotlin.fir.declarations.impl.FirFileImpl.acceptChildren(FirFileImpl.kt:60)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitNestedElements(AbstractDiagnosticCollectorVisitor.kt:44)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitFile(AbstractDiagnosticCollectorVisitor.kt:1351)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor.visitFile(AbstractDiagnosticCollectorVisitor.kt:36)
        at org.jetbrains.kotlin.fir.declarations.FirFile.accept(FirFile.kt:43)
        at org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollector.collectDiagnostics(AbstractDiagnosticCollector.kt:36)
        at org.jetbrains.kotlin.fir.pipeline.AnalyseKt.runCheckers(analyse.kt:37)
        ... 25 more
Caused by: java.lang.IllegalArgumentException: source must not be null
        at org.jetbrains.kotlin.diagnostics.KtDiagnosticReportHelpersKt.requireNotNull(KtDiagnosticReportHelpers.kt:223)
        at org.jetbrains.kotlin.diagnostics.KtDiagnosticReportHelpersKt.reportOn(KtDiagnosticReportHelpers.kt:219)
        at org.jetbrains.kotlin.diagnostics.KtDiagnosticReportHelpersKt.reportOn$default(KtDiagnosticReportHelpers.kt:210)
        at org.jetbrains.kotlin.fir.analysis.checkers.expression.FirFunctionReturnTypeMismatchChecker.check(FirFunctionReturnTypeMismatchChecker.kt:107)
        at org.jetbrains.kotlin.fir.analysis.checkers.expression.FirFunctionReturnTypeMismatchChecker.check(FirFunctionReturnTypeMismatchChecker.kt:31)
        at org.jetbrains.kotlin.fir.analysis.checkers.expression.ExpressionCheckersDiagnosticComponent.visitReturnExpression(ExpressionCheckersDiagnosticComponent.kt:530)
        ... 56 more

I observed that:

• inlining test fixes the issue
• Not having add at the end fixes the issue
• Storing it into a variable before returning also fixes the issue

Therefore I assume it has to do with the return type of test and the add function.