cgen: fix codegen for indexing anon_fn (fix #23493) (#23495)

vlib/v/gen/c/assign.v

@@ -444,7 +444,7 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 						g.is_assign_lhs = false
 						g.is_arraymap_set = false
 						if mut left is ast.IndexExpr {
-							sym := g.table.sym(left.left_type)
+							sym := g.table.final_sym(left.left_type)
 							if sym.kind in [.map, .array] {
 								g.expr(val)
 								g.writeln('});')

vlib/v/tests/indexexpr_with_anon_fn_test.v

@@ -0,0 +1,21 @@
+module main
+
+pub struct Tree {}
+
+pub type TreeBelt = map[string]fn (input &Tree, belt TreeBelt) []&Tree
+
+pub fn (tree &Tree) processed() TreeBelt {
+	mut blet := TreeBelt(map[string]fn (&Tree, TreeBelt) []&Tree{})
+	blet['foo'] = fn (input &Tree, belt TreeBelt) []&Tree {
+		return [input]
+	}
+	return blet
+}
+
+fn test_main() {
+	tree := Tree{}
+	ret := tree.processed()
+	assert ret.len == 1
+	ret2 := ret['foo'](tree, ret)
+	assert ret2[0] == tree
+}