From 7dad6e887e6cadfcfda4b3f2054653116763afb5 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sat, 5 Apr 2025 12:59:28 -0300
Subject: [PATCH] parser,checker,cgen: fix wrong auto heap deref of auto
 `index` loop var (fix #24117) (#24124)

---
 vlib/v/ast/ast.v                                  |  1 +
 vlib/v/checker/checker.v                          |  2 +-
 vlib/v/gen/c/cgen.v                               |  3 ++-
 vlib/v/parser/containers.v                        | 11 ++++++-----
 vlib/v/tests/interfaces/interface_arr_init_test.v |  6 ++++++
 5 files changed, 16 insertions(+), 7 deletions(-)
 create mode 100644 vlib/v/tests/interfaces/interface_arr_init_test.v

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index d768df059..49004758f 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -901,6 +901,7 @@ pub mut:
 	is_arg        bool // fn args should not be autofreed
 	is_auto_deref bool
 	is_unwrapped  bool // ct type smartcast unwrapped
+	is_index_var  bool // index loop var
 	expr          Expr
 	typ           Type
 	orig_type     Type   // original sumtype type; 0 if it's not a sumtype
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 488821c7f..bfb3520f5 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3490,7 +3490,7 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 	} else if !from_type.has_option_or_result() && mut to_sym.info is ast.Interface {
 		if c.type_implements(from_type, to_type, node.pos) {
 			if !from_type.is_any_kind_of_pointer() && from_sym.kind != .interface
-				&& !c.inside_unsafe {
+				&& !c.inside_unsafe && !from_type.is_number() {
 				c.mark_as_referenced(mut &node.expr, true)
 			}
 			if to_sym.info.is_generic {
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 4db024185..92dc01900 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -2814,7 +2814,8 @@ fn (mut g Gen) call_cfn_for_casting_expr(fname string, expr ast.Expr, exp ast.Ty
 			&& (expr.expr is ast.ArrayInit && expr.expr.is_fixed)
 
 		if !is_cast_fixed_array_init && (is_comptime_variant || !expr.is_lvalue()
-			|| (expr is ast.Ident && expr.obj.is_simple_define_const())) {
+			|| (expr is ast.Ident && (expr.obj.is_simple_define_const()
+			|| (expr.obj is ast.Var && expr.obj.is_index_var)))) {
 			// Note: the `_to_sumtype_` family of functions do call memdup internally, making
 			// another duplicate with the HEAP macro is redundant, so use ADDR instead:
 			if expr.is_as_cast() {
diff --git a/vlib/v/parser/containers.v b/vlib/v/parser/containers.v
index aec3ea9f6..0dfef0ab8 100644
--- a/vlib/v/parser/containers.v
+++ b/vlib/v/parser/containers.v
@@ -267,11 +267,12 @@ fn (mut p Parser) map_init() ast.MapInit {
 
 fn (mut p Parser) scope_register_index() {
 	p.scope.objects['index'] = ast.Var{ // override index variable if it already exist, else create index variable
-		name:    'index'
-		pos:     p.tok.pos()
-		typ:     ast.int_type
-		is_mut:  false
-		is_used: false
+		name:         'index'
+		pos:          p.tok.pos()
+		typ:          ast.int_type
+		is_mut:       false
+		is_used:      false
+		is_index_var: true
 	}
 	p.scope.objects['it'] = ast.Var{ // it is now deprecated, will be removed in future stable release
 		name:    'it'
diff --git a/vlib/v/tests/interfaces/interface_arr_init_test.v b/vlib/v/tests/interfaces/interface_arr_init_test.v
new file mode 100644
index 000000000..9792a73f6
--- /dev/null
+++ b/vlib/v/tests/interfaces/interface_arr_init_test.v
@@ -0,0 +1,6 @@
+interface Values {}
+
+fn test_main() {
+	a := []Values{len: 4, init: Values(index)}
+	assert '${a}' == '[Values(0), Values(1), Values(2), Values(3)]'
+}
-- 
2.39.5