From 7c780ed8fa89c33e677020b6a0b93dd472932514 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sat, 30 Aug 2025 17:40:47 -0300
Subject: [PATCH] cgen, markused, checker: fix iteration over mutable option
 (fix #24860) (#25199)

---
 vlib/v/checker/for.v                       |  3 +++
 vlib/v/gen/c/assign.v                      | 12 +++++++++++-
 vlib/v/markused/walker.v                   |  4 ++++
 vlib/v/tests/options/option_for_mut_test.v | 15 +++++++++++++++
 4 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/options/option_for_mut_test.v

diff --git a/vlib/v/checker/for.v b/vlib/v/checker/for.v
index 1643ac172..bb68ef989 100644
--- a/vlib/v/checker/for.v
+++ b/vlib/v/checker/for.v
@@ -254,6 +254,9 @@ fn (mut c Checker) for_in_stmt(mut node ast.ForInStmt) {
 			}
 			if node.val_is_mut {
 				value_type = value_type.ref()
+				if value_type.has_flag(.option) {
+					value_type = value_type.set_flag(.option_mut_param_t)
+				}
 				match mut node.cond {
 					ast.Ident {
 						if mut node.cond.obj is ast.Var {
diff --git a/vlib/v/gen/c/assign.v b/vlib/v/gen/c/assign.v
index 9f5d7f94e..2b4a15843 100644
--- a/vlib/v/gen/c/assign.v
+++ b/vlib/v/gen/c/assign.v
@@ -866,9 +866,19 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 							g.write('*')
 						}
 						if node_.op == .assign && var_type.has_flag(.option_mut_param_t) {
+							if val is ast.CastExpr {
+								g.expr(left)
+								g.write('->state = ')
+								g.expr(val)
+								g.writeln('.state;')
+							}
 							g.write('memcpy(&')
 							g.expr(left)
-							g.write('->data, *(${g.styp(val_type)}**)&')
+							if val is ast.CastExpr {
+								g.write('->data, ')
+							} else {
+								g.write('->data, *(${g.styp(val_type)}**)&')
+							}
 						} else if var_type.has_flag(.option_mut_param_t) {
 							g.expr(left)
 							g.write(' = ')
diff --git a/vlib/v/markused/walker.v b/vlib/v/markused/walker.v
index a7a286a72..f378d4244 100644
--- a/vlib/v/markused/walker.v
+++ b/vlib/v/markused/walker.v
@@ -1300,6 +1300,10 @@ fn (mut w Walker) mark_resource_dependencies() {
 		w.fn_by_name(builderptr_idx + '.write_string')
 		w.fn_by_name('strings.new_builder')
 		w.uses_free[ast.string_type] = true
+
+		if w.table.dumps.keys().any(ast.Type(u32(it)).has_flag(.option)) {
+			w.fn_by_name('str_intp')
+		}
 	}
 	if w.features.auto_str_ptr {
 		w.fn_by_name('isnil')
diff --git a/vlib/v/tests/options/option_for_mut_test.v b/vlib/v/tests/options/option_for_mut_test.v
new file mode 100644
index 000000000..37650f5f5
--- /dev/null
+++ b/vlib/v/tests/options/option_for_mut_test.v
@@ -0,0 +1,15 @@
+module main
+
+fn test_main() {
+	mut data := [3]?int{}
+
+	for mut d in data {
+		d = ?int(1)
+		assert '${d}' == 'Option(1)'
+	}
+
+	for i in 0 .. data.len {
+		data[i] = ?int(3)
+	}
+	assert '${data}' == '[Option(3), Option(3), Option(3)]'
+}
-- 
2.39.5