checker: fix array fixed unresolved return check and resolver (fix #25774) (#25790)

Author: felipensp

vlib/v/checker/checker.v

@@ -5913,7 +5913,13 @@ pub fn (mut c Checker) update_unresolved_fixed_sizes() {
 			ret_sym := c.table.sym(stmt.return_type)
 			if ret_sym.info is ast.ArrayFixed && c.array_fixed_has_unresolved_size(ret_sym.info) {
 				mut size_expr := ret_sym.info.size_expr
+				old_typ := c.cast_fixed_array_ret(stmt.return_type, c.table.final_sym(stmt.return_type))
 				stmt.return_type = c.eval_array_fixed_sizes(mut size_expr, 0, ret_sym.info.elem_type)
+				new_sym := c.table.sym(stmt.return_type)
+				mut typ_sym := c.table.type_symbols[old_typ.idx()]
+				typ_sym.name = new_sym.name
+				typ_sym.cname = new_sym.cname
+				typ_sym.info = new_sym.info
 			}
 		} else if mut stmt is ast.TypeDecl { // alias
 			mut alias_decl := stmt

vlib/v/checker/return.v

@@ -278,6 +278,11 @@ fn (mut c Checker) return_stmt(mut node ast.Return) {
 				if c.inside_lambda && exp_type.has_flag(.generic) {
 					continue
 				}
+				if exp_final_sym.info is ast.ArrayFixed
+					&& c.array_fixed_has_unresolved_size(exp_final_sym.info) {
+					continue
+				}
+
 				c.error('cannot use `${got_type_name}` as ${c.error_type_name(exp_type)} in return argument',
 					exprv.pos())
 			}

vlib/v/gen/c/cgen.v

@@ -7034,8 +7034,8 @@ fn (mut g Gen) write_types(symbols []&ast.TypeSymbol) {
 			ast.ArrayFixed {
 				elem_sym := g.table.sym(sym.info.elem_type)
 				if !elem_sym.is_builtin() && !sym.info.elem_type.has_flag(.generic)
-					&& (!g.pref.skip_unused || (!sym.info.is_fn_ret
-					&& sym.idx in g.table.used_features.used_syms)) {
+					&& !sym.info.is_fn_ret && (!g.pref.skip_unused
+					|| (!sym.info.is_fn_ret && sym.idx in g.table.used_features.used_syms)) {
 					// .array_fixed {
 					styp := sym.cname
 					// array_fixed_char_300 => char x[300]

vlib/v/tests/fns/array_fixed_unresolved_ret_test.v

@@ -0,0 +1,17 @@
+enum Abc {
+	a = 1
+	b = 2
+	c = 3
+}
+
+const abc_len = int(Abc.c)
+
+fn build_arr() [abc_len]Abc {
+	return [abc_len]Abc{}
+}
+
+fn test_main() {
+	a := build_arr()
+	println(a)
+	assert a.len == 3
+}