From 1ccdcb8f3b7ce729de0b147dff5ecff6389cc1e0 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 15:14:44 +0300
Subject: [PATCH] builder: fix module builder error (fixes #20147)

---
 ...vmodules_package_compile_regression_test.v | 77 +++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 vlib/v/tests/vmodules_package_compile_regression_test.v

diff --git a/vlib/v/tests/vmodules_package_compile_regression_test.v b/vlib/v/tests/vmodules_package_compile_regression_test.v
new file mode 100644
index 000000000..e8dcbd1d8
--- /dev/null
+++ b/vlib/v/tests/vmodules_package_compile_regression_test.v
@@ -0,0 +1,77 @@
+import os
+
+@[markused]
+const turn_off_vcolors = os.setenv('VCOLORS', 'never', true)
+
+const issue_20147_vexe = @VEXE
+
+fn issue_20147_env_snapshot(name string) (string, bool) {
+	val := os.getenv_opt(name) or { return '', false }
+	return val, true
+}
+
+fn issue_20147_restore_env(name string, value string, existed bool) {
+	if existed {
+		os.setenv(name, value, true)
+	} else {
+		os.unsetenv(name)
+	}
+}
+
+fn issue_20147_workspace() string {
+	return os.join_path(os.vtmp_dir(), 'issue_20147_vmodules_package_compile')
+}
+
+fn issue_20147_module_root() string {
+	return os.join_path(issue_20147_workspace(), '.vmodules', 'msgpack')
+}
+
+fn issue_20147_write_file(path string, contents string) {
+	os.write_file(path, contents) or { panic(err) }
+}
+
+fn issue_20147_write_project() {
+	basepath := issue_20147_module_root()
+	vmod_contents := ['Module {', "\tname: 'msgpack'", '}'].join_lines() + '\n'
+	config_contents :=
+		['module config', '', 'pub struct Config {}', '', 'pub fn default_config() Config {', '\treturn Config{}', '}'].join_lines() +
+		'\n'
+	decoder_contents := ['module decoder', '', 'pub struct Decoder {}'].join_lines() + '\n'
+	to_contents := ['module msgpack.to', '', 'pub fn new_decoder(src []u8) {}'].join_lines() + '\n'
+	msgpack_contents :=
+		['module msgpack', '', "pub const description = 'an empty module, used as a placeholder, for other modules'"].join_lines() +
+		'\n'
+	test_contents := ['fn test_a() {', '\tassert true', '}'].join_lines()
+	import_config_test_contents := ['import msgpack.config', '', test_contents].join_lines() + '\n'
+	import_decoder_test_contents := ['import decoder', '', test_contents].join_lines() + '\n'
+	import_to_test_contents := ['import msgpack.config', '', test_contents].join_lines() + '\n'
+	os.rmdir_all(issue_20147_workspace()) or {}
+	os.mkdir_all(os.join_path(basepath, 'config')) or { panic(err) }
+	os.mkdir_all(os.join_path(basepath, 'decoder')) or { panic(err) }
+	os.mkdir_all(os.join_path(basepath, 'to')) or { panic(err) }
+	issue_20147_write_file(os.join_path(basepath, 'v.mod'), vmod_contents)
+	issue_20147_write_file(os.join_path(basepath, 'config', 'config.v'), config_contents)
+	issue_20147_write_file(os.join_path(basepath, 'decoder', 'decoder.v'), decoder_contents)
+	issue_20147_write_file(os.join_path(basepath, 'to', 'to.v'), to_contents)
+	issue_20147_write_file(os.join_path(basepath, 'msgpack.v'), msgpack_contents)
+	issue_20147_write_file(os.join_path(basepath, 'import_config_test.v'),
+		import_config_test_contents)
+	issue_20147_write_file(os.join_path(basepath, 'import_decoder_test.v'),
+		import_decoder_test_contents)
+	issue_20147_write_file(os.join_path(basepath, 'import_to_test.v'), import_to_test_contents)
+}
+
+fn test_issue_20147_vmodules_package_tests_compile() {
+	issue_20147_write_project()
+	old_wd := os.getwd()
+	old_vmodules, had_vmodules := issue_20147_env_snapshot('VMODULES')
+	os.setenv('VMODULES', os.join_path(issue_20147_workspace(), '.vmodules'), true)
+	os.chdir(issue_20147_module_root()) or { panic(err) }
+	defer {
+		os.chdir(old_wd) or { panic(err) }
+		issue_20147_restore_env('VMODULES', old_vmodules, had_vmodules)
+		os.rmdir_all(issue_20147_workspace()) or {}
+	}
+	res := os.execute('${os.quoted_path(issue_20147_vexe)} test .')
+	assert res.exit_code == 0, res.output
+}
-- 
2.39.5