[tests] Add test data for KT-63840

compiler/testData/diagnostics/tests/builderInference/issues/kt63840a.fir.kt

@@ -0,0 +1,32 @@
+// ISSUE: KT-63840
+// CHECK_TYPE_WITH_EXACT
+// WITH_STDLIB
+
+fun test() {
+    val buildee = build {
+        select(
+            replaceTypeVariable(TargetType()),
+            DifferentType()
+        )
+    }
+    // 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)
+}
+
+
+
+
+fun <T> select(vararg values: T): T = values.first()
+
+class TargetType
+class DifferentType
+
+class Buildee<TV> {
+    fun replaceTypeVariable(value: TV): TV { val temp = storage; storage = value; return temp }
+    private var storage: TV = null!!
+}
+
+fun <PTV> build(instructions: Buildee<PTV>.() -> Unit): Buildee<PTV> {
+    return Buildee<PTV>().apply(instructions)
+}