[tests] Add test data for KT-59426

compiler/testData/codegen/box/builderInference/issues/kt59426.kt

@@ -0,0 +1,38 @@
+// ISSUE: KT-59426
+
+// IGNORE_LIGHT_ANALYSIS
+// IGNORE_BACKEND_K1: ANY
+// REASON: red code (see corresponding diagnostic test)
+
+// IGNORE_BACKEND_K2: JVM_IR, WASM
+// REASON: run-time failure (java.lang.ClassCastException: DifferentType cannot be cast to TargetType @ Kt59426Kt.consumeBuildeeReceiver)
+
+fun box(): String {
+    build {
+        setTypeVariable(DifferentType())
+        consumeBuildeeReceiver()
+    }
+    return "OK"
+}
+
+
+
+
+class TargetType
+class DifferentType
+
+fun consumeTargetType(value: TargetType) {}
+
+class Buildee<TV> {
+    fun setTypeVariable(value: TV) { storage = value }
+    fun getTypeVariable(): TV = storage
+    private var storage: TV = TargetType() as TV
+}
+
+fun Buildee<TargetType>.consumeBuildeeReceiver() {
+    consumeTargetType(getTypeVariable())
+}
+
+fun <PTV> build(instructions: Buildee<PTV>.() -> Unit): Buildee<PTV> {
+    return Buildee<PTV>().apply(instructions)
+}

compiler/testData/diagnostics/tests/builderInference/issues/kt59426.fir.kt

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+// ISSUE: KT-59426
+// CHECK_TYPE_WITH_EXACT
+
+fun test() {
+    val buildee = build {
+        setTypeVariable(DifferentType())
+        consumeBuildeeReceiver()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<TargetType>>(buildee)
+}
+
+
+
+
+class TargetType
+class DifferentType
+
+fun consumeTargetType(value: TargetType) {}
+
+class Buildee<TV> {
+    fun setTypeVariable(value: TV) { storage = value }
+    fun getTypeVariable(): TV = storage
+    private var storage: TV = null!!
+}
+
+fun Buildee<TargetType>.consumeBuildeeReceiver() {
+    consumeTargetType(getTypeVariable())
+}
+
+fun <PTV> build(instructions: Buildee<PTV>.() -> Unit): Buildee<PTV> {
+    return Buildee<PTV>().apply(instructions)
+}

compiler/testData/diagnostics/tests/builderInference/issues/kt59426.kt

@@ -0,0 +1,34 @@
+// ISSUE: KT-59426
+// CHECK_TYPE_WITH_EXACT
+
+fun test() {
+    val buildee = build {
+        setTypeVariable(<!TYPE_MISMATCH("TargetType; DifferentType")!>DifferentType()<!>)
+        <!RECEIVER_TYPE_MISMATCH("TargetType; DifferentType")!>consumeBuildeeReceiver<!>()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<TargetType>>(buildee)
+}
+
+
+
+
+class TargetType
+class DifferentType
+
+fun consumeTargetType(value: TargetType) {}
+
+class Buildee<TV> {
+    fun setTypeVariable(value: TV) { storage = value }
+    fun getTypeVariable(): TV = storage
+    private var storage: TV = null!!
+}
+
+fun Buildee<TargetType>.consumeBuildeeReceiver() {
+    consumeTargetType(getTypeVariable())
+}
+
+fun <PTV> build(instructions: Buildee<PTV>.() -> Unit): Buildee<PTV> {
+    return Buildee<PTV>().apply(instructions)
+}