cgen: fix interface heap allocate pointing to same value (fix #25354) (#25359)

vlib/v/gen/c/cgen.v

@@ -2914,9 +2914,13 @@ fn (mut g Gen) call_cfn_for_casting_expr(fname string, expr ast.Expr, exp ast.Ty
 		is_cast_fixed_array_init := expr is ast.CastExpr
 			&& (expr.expr is ast.ArrayInit && expr.expr.is_fixed)
 
+		is_primitive_to_interface := fname.contains('_to_Interface_') && expr is ast.Ident
+			&& g.table.sym(got).kind in [.i8, .i16, .i32, .int, .i64, .isize, .u8, .u16, .u32, .u64, .usize, .f32, .f64, .bool, .rune]
+
 		if !is_cast_fixed_array_init && (is_comptime_variant || !expr.is_lvalue()
 			|| (expr is ast.Ident && (expr.obj.is_simple_define_const()
-			|| (expr.obj is ast.Var && expr.obj.is_index_var)))) {
+			|| (expr.obj is ast.Var && expr.obj.is_index_var)))
+			|| is_primitive_to_interface) {
 			// 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() {

vlib/v/tests/interfaces/interface_mut_value_update_test.v

@@ -0,0 +1,34 @@
+interface Value {}
+
+struct Foo {
+mut:
+	value int
+}
+
+fn test_main() {
+	mut i := 0
+	mut integers := []Value{}
+	integers << i
+	i = 1
+	integers << i
+	i = 2
+	integers << i
+	assert integers == [0, 1, 2]
+
+	mut f := Foo{
+		value: 0
+	}
+	mut foos := []Foo{}
+	foos << f
+	f.value = 1
+	foos << f
+	f.value = 2
+	foos << f
+	assert foos == [Foo{
+		value: 0
+	}, Foo{
+		value: 1
+	}, Foo{
+		value: 2
+	}]
+}