context: small refactor to always use Context type instead of multiple types (#9705)

vlib/context/deadline_test.v

@@ -0,0 +1,63 @@
+import context
+import time
+
+const (
+	// a reasonable duration to block in an example
+	short_duration = 1 * time.millisecond
+)
+
+fn after(dur time.Duration) chan int {
+	dst := chan int{}
+	go fn (dur time.Duration, dst chan int) {
+		time.sleep(dur)
+		dst <- 0
+	}(dur, dst)
+	return dst
+}
+
+// This example passes a context with an arbitrary deadline to tell a blocking
+// function that it should abandon its work as soon as it gets to it.
+fn test_with_deadline() {
+	dur := time.now().add(short_duration)
+	ctx := context.with_deadline(context.background(), dur)
+
+	defer {
+		// Even though ctx will be expired, it is good practice to call its
+		// cancellation function in any case. Failure to do so may keep the
+		// context and its parent alive longer than necessary.
+		context.cancel(ctx)
+	}
+
+	after_ch := after(1 * time.second)
+	ctx_ch := ctx.done()
+	select {
+		_ := <-after_ch {
+			assert false
+		}
+		_ := <-ctx_ch {
+			assert true
+		}
+	}
+}
+
+// This example passes a context with a timeout to tell a blocking function that
+// it should abandon its work after the timeout elapses.
+fn test_with_timeout() {
+	// Pass a context with a timeout to tell a blocking function that it
+	// should abandon its work after the timeout elapses.
+	ctx := context.with_timeout(context.background(), short_duration)
+	defer {
+		context.cancel(ctx)
+	}
+
+	after_ch := after(1 * time.second)
+	ctx_ch := ctx.done()
+	select {
+		_ := <-after_ch {
+			assert false
+		}
+		_ := <-ctx_ch {
+			assert true
+		}
+	}
+}