all: implement ch <- x or {...} and ch <- x ? (#7928)

vlib/sync/channel_push_or_1_test.v

@@ -0,0 +1,67 @@
+const n = 1000
+const c = 100
+
+fn f(ch chan int) {
+	for _ in 0 .. n {
+		_ := <-ch
+	}
+	ch.close()
+}
+
+fn test_push_or_unbuffered() {
+	ch := chan int{}
+	go f(ch)
+	mut j := 0
+	for {
+		ch <- j or {
+			break
+		}
+		j++
+	}
+	assert j == n
+}
+
+fn test_push_or_buffered() {
+	ch := chan int{cap: c}
+	go f(ch)
+	mut j := 0
+	for {
+		ch <- j or {
+			break
+		}
+		j++
+	}
+	// we don't know how many elements are in the buffer when the channel
+	// is closed, so check j against an interval
+	assert j >= n
+	assert j <= n + c
+}
+
+fn g(ch chan int, res chan int) {
+	mut j := 0
+	for {
+		ch <- j or {
+			break
+		}
+		j++
+	}
+	println('done $j')
+	res <- j
+}
+
+fn test_many_senders() {
+	ch := chan int{}
+	res := chan int{}
+	go g(ch, res)
+	go g(ch, res)
+	go g(ch, res)
+	mut k := 0
+	for _ in 0 .. 3 * n {
+		k = <-ch
+	}
+	ch.close()
+	mut sum := <-res
+	sum += <-res
+	sum += <-res
+	assert sum == 3 * n
+}