cgen: fix `for match {...} {` and `for select {...} {` (#6441)

vlib/v/checker/checker.v

@@ -2295,6 +2295,7 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 		}
 		ast.ForStmt {
 			c.in_for_count++
+			c.expected_type = table.bool_type
 			typ := c.expr(node.cond)
 			if !node.is_inf && typ.idx() != table.bool_type_idx && !c.pref.translated {
 				c.error('non-bool used as for condition', node.pos)

vlib/v/gen/cgen.v

@@ -897,13 +897,15 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 		ast.ForStmt {
 			g.write_v_source_line_info(node.pos)
 			g.is_vlines_enabled = false
-			g.write('while (')
-			if node.is_inf {
-				g.write('1')
-			} else {
+			g.writeln('for (;;) {')
+			if !node.is_inf {
+				g.indent++
+				g.stmt_path_pos << g.out.len
+				g.write('if (!(')
 				g.expr(node.cond)
+				g.writeln(')) break;')
+				g.indent--
 			}
-			g.writeln(') {')
 			g.is_vlines_enabled = true
 			g.stmts(node.stmts)
 			g.writeln('}')
@@ -2888,6 +2890,7 @@ fn (mut g Gen) select_expr(node ast.SelectExpr) {
 	}
 	g.writeln('}')
 	if is_expr {
+		g.empty_line = false
 		g.write(cur_line)
 		g.write('($select_result != -2)')
 	}

vlib/v/tests/for_loops_2_test.v

@@ -0,0 +1,55 @@
+fn test_for_match() {
+	mut a := 2
+	mut b := 0
+	for match a {
+		2 {
+			println('a == 2')
+			a = 0
+			true
+		}
+		0 {
+			println('a == 0')
+			a = 5
+			false
+		}
+		else {
+			println('unexpected branch')
+			false
+		}
+	} {
+		b++
+		println('${b}. run')
+	}
+	assert a == 5
+	assert b == 1
+}
+
+fn test_for_select() {
+	ch1 := chan int{}
+	ch2 := chan f64{}
+	go do_send(ch1, ch2)
+	mut a := 0
+	mut b := 0
+	for select {
+		x := <-ch1 {
+			a += x
+		}
+		y := <- ch2 {
+			a += int(y)
+		}
+	} {
+		// count number of receive events
+		b++
+		println('${b}. event')
+	}
+	assert a == 10
+	assert b == 3
+}
+
+fn do_send(ch1 chan int, ch2 chan f64) {
+	ch1 <- 3
+	ch2 <- 5.0
+	ch2.close()
+	ch1 <- 2
+	ch1.close()
+}