From ab707dce5c84f4ea4f9ad5ccc24e0e123837236b Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Mon, 30 Dec 2024 19:26:39 -0300
Subject: [PATCH] checker: fix `for` iterator method `.next()`, not marked as
 used (fix #23312) (#23321)

---
 vlib/v/checker/for.v                          |  2 ++
 .../skip_unused/generic_iterator_loop.run.out |  0
 .../generic_iterator_loop.skip_unused.run.out |  0
 .../skip_unused/generic_iterator_loop.vv      | 23 +++++++++++++++++++
 4 files changed, 25 insertions(+)
 create mode 100644 vlib/v/tests/skip_unused/generic_iterator_loop.run.out
 create mode 100644 vlib/v/tests/skip_unused/generic_iterator_loop.skip_unused.run.out
 create mode 100644 vlib/v/tests/skip_unused/generic_iterator_loop.vv

diff --git a/vlib/v/checker/for.v b/vlib/v/checker/for.v
index 6e1dc735636a61..9ef3e116b3a492 100644
--- a/vlib/v/checker/for.v
+++ b/vlib/v/checker/for.v
@@ -173,6 +173,8 @@ fn (mut c Checker) for_in_stmt(mut node ast.ForInStmt) {
 			unwrapped_typ := c.unwrap_generic(typ)
 			unwrapped_sym := c.table.sym(unwrapped_typ)
 
+			c.table.used_features.comptime_calls['${int(unwrapped_typ)}.next'] = true
+
 			if node.key_var.len > 0 {
 				key_type := match unwrapped_sym.kind {
 					.map { unwrapped_sym.map_info().key_type }
diff --git a/vlib/v/tests/skip_unused/generic_iterator_loop.run.out b/vlib/v/tests/skip_unused/generic_iterator_loop.run.out
new file mode 100644
index 00000000000000..e69de29bb2d1d6
diff --git a/vlib/v/tests/skip_unused/generic_iterator_loop.skip_unused.run.out b/vlib/v/tests/skip_unused/generic_iterator_loop.skip_unused.run.out
new file mode 100644
index 00000000000000..e69de29bb2d1d6
diff --git a/vlib/v/tests/skip_unused/generic_iterator_loop.vv b/vlib/v/tests/skip_unused/generic_iterator_loop.vv
new file mode 100644
index 00000000000000..b34e36d70d0843
--- /dev/null
+++ b/vlib/v/tests/skip_unused/generic_iterator_loop.vv
@@ -0,0 +1,23 @@
+module main
+
+struct Foo {}
+
+fn (f Foo) next() ?Foo {
+	return none
+}
+
+struct Bar {}
+
+fn (f Bar) next() ?Bar {
+	return none
+}
+
+fn loop[T](iter T) {
+	for _ in iter {
+	}
+}
+
+fn main() {
+	loop(Foo{})
+	loop(Bar{})
+}