Plugin behaves abnormally when add is called in a function

[mattbaumann]

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.

[koperagen]

Hi! Thank you for reporting this issue.

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

Indeed, checker cannot report an error diagnostic "mismatched return type" because expression is not correctly transformed by the plugin. Correct behaviour here would be failed compilation due to a diagnostic error instead of an unclear exception.
Another workaround:cast<Iso6393Raw>(verify = true) after add

I'll see how to have diagnostic correctly reported

[zaleslaw]

Dear @mattbaumann,
I’d love to ask you a few questions about your use cases or have a brief chat. We’re currently seeking early users of the Compiler Plugin to help us improve the UX before the major release. It should only take a short amount of your time.

You could reach me here or here with the name @zaleslaw

[mattbaumann]

Sure, I was on vacation last week, I'll contact you tomorrow. c82d3bcc-f438-4f84-95d8-11ce1101612c at Tue Oct 21 14:14:50 2025 CEST