channels: make `ch.len` and `ch.cap` available as properties (#6221)

vlib/sync/channel_fill_test.v

@@ -5,18 +5,18 @@ const (
 	queue_fill = 763
 )
 
-fn do_send(mut ch sync.Channel, fin sync.Semaphore) {
+fn do_send(ch chan int, fin sync.Semaphore) {
 	for i in 0 .. queue_fill {
-		ch.push(&i)
+		ch <- i
 	}
 	fin.post()
 }
 
 fn test_channel_len_cap() {
-	mut ch := sync.new_channel<int>(queue_len)
+	ch := chan int{cap: queue_len}
 	sem := sync.new_semaphore()
-	go do_send(mut ch, sem)
+	go do_send(ch, sem)
 	sem.wait()
 	assert ch.cap == queue_len
-	assert ch.len() == queue_fill
+	assert ch.len == queue_fill
 }

vlib/v/checker/checker.v

@@ -1470,8 +1470,8 @@ pub fn (mut c Checker) selector_expr(mut selector_expr ast.SelectorExpr) table.T
 	sym := c.table.get_type_symbol(c.unwrap_generic(typ))
 	field_name := selector_expr.field_name
 	// variadic
-	if typ.has_flag(.variadic) || sym.kind == .array_fixed {
+	if typ.has_flag(.variadic) || sym.kind == .array_fixed || sym.kind == .chan {
-		if field_name == 'len' {
+		if field_name == 'len' || (sym.kind == .chan && field_name == 'cap') {
 			selector_expr.typ = table.int_type
 			return table.int_type
 		}
@@ -3262,6 +3262,9 @@ pub fn (mut c Checker) chan_init(mut node ast.ChanInit) table.Type {
 	if node.typ != 0 {
 		info := c.table.get_type_symbol(node.typ).chan_info()
 		node.elem_type = info.elem_type
+		if node.has_cap {
+			c.check_array_init_para_type('cap', node.cap_expr, node.pos)
+		}
 		return node.typ
 	} else {
 		c.error('`chan` of unknown type', node.pos)

vlib/v/gen/cgen.v

@@ -2107,8 +2107,14 @@ fn (mut g Gen) expr(node ast.Expr) {
 				g.write('$info.size')
 				return
 			}
+			if sym.kind == .chan && node.field_name == 'len' {
+				g.write('sync__Channel_len(')
 				g.expr(node.expr)
-			if node.expr_type.is_ptr() {
+				g.write(')')
+				return
+			}
+			g.expr(node.expr)
+			if node.expr_type.is_ptr() || sym.kind == .chan {
 				g.write('->')
 			} else {
 				// g.write('. /*typ=  $it.expr_type */') // ${g.typ(it.expr_type)} /')