[Tests] Test samples from KEEP

compiler/testData/diagnostics/tests/extensions/contextReceivers/fromKEEP/monoidSum.kt

@@ -0,0 +1,32 @@
+interface Semigroup<T> {
+    infix fun T.combine(other: T): T
+}
+
+interface Monoid<T> : Semigroup<T> {
+    val unit: T
+}
+object IntMonoid : Monoid<Int> {
+    override fun Int.combine(other: Int): Int = this + other
+    override val unit: Int = 0
+}
+object StringMonoid : Monoid<String> {
+    override fun String.combine(other: String): String = this + other
+    override val unit: String = ""
+}
+
+public inline fun <T, R> Iterable<T>.fold(initial: R, operation: (acc: R, T) -> R): R = TODO()
+
+context(Monoid<T>)
+fun <T> List<T>.sum(): T = fold(unit) { acc, e -> acc.combine(e) }
+
+fun <T> listOf(vararg items: T): List<T> = null!!
+
+fun test() {
+    with(IntMonoid) {
+        listOf(1, 2, 3).sum()
+    }
+    with(StringMonoid) {
+        listOf(1, 2, 3).<!NO_CONTEXT_RECEIVER!>sum()<!>
+        listOf("1", "2", "3").sum()
+    }
+}