parser,checker: smart detect or {} inside loop when using c <-val (fix #24550) (#25435)

Author: Delta456

vlib/v/checker/checker.v

@@ -2339,6 +2339,14 @@ fn (mut c Checker) stmt(mut node ast.Stmt) {
 							c.error('unused expression', node.pos)
 						}
 					}
+					if node.expr.op == .arrow {
+						if mut node.expr.right is ast.CallExpr {
+							if node.expr.right.return_type.has_flag(.result) {
+								node.expr.or_block.err_used = node.expr.or_block.scope.known_var('err')
+								node.expr.right.or_block = node.expr.or_block
+							}
+						}
+					}
 				}
 			}
 			if !c.inside_return {

vlib/v/parser/expr.v

@@ -827,6 +827,17 @@ fn (mut p Parser) infix_expr(left ast.Expr) ast.Expr {
 	mut or_scope := &ast.Scope(unsafe { nil })
 	// allow `x := <-ch or {...}` to handle closed channel
 	if op == .arrow {
+		if mut right is ast.SelectorExpr {
+			or_kind = right.or_block.kind
+			or_stmts = right.or_block.stmts.clone()
+			right.or_block = ast.OrExpr{}
+		}
+		if mut right is ast.CallExpr {
+			or_kind = right.or_block.kind
+			or_stmts = right.or_block.stmts.clone()
+			or_scope = right.or_block.scope
+			right.or_block = ast.OrExpr{}
+		}
 		if p.tok.kind == .key_orelse {
 			or_kind = .block
 			or_stmts, or_pos, or_scope = p.or_block(.with_err_var)

vlib/v/slow_tests/inout/for_channel_or_expr_block.out

@@ -0,0 +1 @@
+[vlib/v/slow_tests/inout/for_channel_or_expr_block.vv:22] a.any(it in [i64(1), 2, 3, 4, 5, 6, 7]): true

vlib/v/slow_tests/inout/for_channel_or_expr_block.vv

@@ -0,0 +1,31 @@
+import time
+
+fn writer(c chan i64, delay i64) {
+	for {
+		time.sleep(delay)
+
+		c <- time.now().day_of_week() or {
+			break
+		}
+	}
+}
+
+fn reader(c chan i64, max int) {
+	mut a := []i64{}
+	for {
+		a << <-c
+		if a.len > max {
+			c.close()
+			break
+		}
+	}
+	dump(a.any(it in [i64(1), 2, 3, 4, 5, 6, 7]))
+}
+
+fn main() {
+	c := chan i64{}
+	mut t := []thread{}
+	t << spawn reader(c, 0)
+	t << spawn writer(c, 10 * time.millisecond)
+	t.wait()
+}