checker, cgen: fix const initialized with array (#21131)

vlib/v/checker/checker.v

@@ -1732,6 +1732,7 @@ fn (mut c Checker) const_decl(mut node ast.ConstDecl) {
 		prev_const_var := c.const_var
 		c.const_var = unsafe { field }
 		mut typ := c.check_expr_option_or_result_call(field.expr, c.expr(mut field.expr))
+		typ = c.cast_fixed_array_ret(typ, c.table.sym(typ))
 		if ct_value := c.eval_comptime_const_expr(field.expr, 0) {
 			field.comptime_expr_value = ct_value
 			if ct_value is u64 {

vlib/v/gen/c/cgen.v

@@ -5986,6 +5986,9 @@ fn (mut g Gen) const_decl_init_later(mod string, name string, expr ast.Expr, typ
 			init.writeln(g.expr_string_surround('\t${cname} = *(${styp}*)', expr, '.data;'))
 		} else if expr is ast.ArrayInit && (expr as ast.ArrayInit).has_index {
 			init.writeln(g.expr_string_surround('\tmemcpy(&${cname}, &', expr, ', sizeof(${styp}));'))
+		} else if expr is ast.CallExpr
+			&& g.table.final_sym(g.unwrap_generic((expr as ast.CallExpr).return_type)).kind == .array_fixed {
+			init.writeln(g.expr_string_surround('\tmemcpy(&${cname}, ', expr, ', sizeof(${styp}));'))
 		} else {
 			init.writeln(g.expr_string_surround('\t${cname} = ', expr, ';'))
 		}

vlib/v/tests/const_array_test.v

@@ -0,0 +1,17 @@
+const some_arr = make_array()
+const some_arr2 = make_array2()
+
+fn make_array() [64]u8 {
+	mut arr := [64]u8{}
+	return arr
+}
+
+fn make_array2() []u8 {
+	mut arr := []u8{}
+	return arr
+}
+
+fn test_main() {
+	assert some_arr.len == 64
+	assert some_arr2.len == 0
+}