cgen: fix shared array indexing (fix #23410) (#23413)

vlib/v/gen/c/index.v

@@ -372,6 +372,9 @@ fn (mut g Gen) index_of_fixed_array(node ast.IndexExpr, sym ast.TypeSymbol) {
 		} else {
 			g.expr(node.left)
 		}
+		if node.left_type.has_flag(.shared_f) {
+			g.write('.val')
+		}
 	}
 	g.write('[')
 	if g.is_direct_array_access || g.pref.translated || node.index is ast.IntegerLiteral {

vlib/v/tests/concurrency/shared_array_indexing_test.v

@@ -0,0 +1,18 @@
+struct Foo {
+mut:
+	bar shared [10]bool
+}
+
+fn test_main() {
+	mut a := Foo{
+		bar: [10]bool{}
+	}
+	lock a.bar {
+		a.bar[0] = true
+		a.bar[1] = false
+	}
+	rlock a.bar {
+		assert a.bar[0] == true
+		assert a.bar[1] == false
+	}
+}