test(web): fail when two packages claim the same world error code

pkg/web/error_codes_test.go

@@ -0,0 +1,84 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package web
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"sort"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+var errCodeConstRegex = regexp.MustCompile(`\bErrCode(\w+)\s*=\s*(\d+)\b`)
+
+// TestErrorCodesAreUnique guards the world-error code space, which is flat across all packages:
+// clients (and the frontend translations) map a code to a message without knowing which package
+// raised it, so two packages picking the same number silently mislabels one of them.
+func TestErrorCodesAreUnique(t *testing.T) {
+	_, thisFile, _, ok := runtime.Caller(0)
+	require.True(t, ok)
+	pkgDir := filepath.Dir(filepath.Dir(thisFile))
+
+	codes := make(map[string][]string)
+	err := filepath.WalkDir(pkgDir, func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() || !strings.HasSuffix(path, ".go") {
+			return nil
+		}
+
+		content, err := os.ReadFile(path)
+		if err != nil {
+			return err
+		}
+
+		for _, match := range errCodeConstRegex.FindAllStringSubmatch(string(content), -1) {
+			codes[match[2]] = append(codes[match[2]], "ErrCode"+match[1])
+		}
+		return nil
+	})
+	require.NoError(t, err)
+	require.NotEmpty(t, codes, "no error code constants found, the test is not looking at the right place")
+
+	duplicates := []string{}
+	for code, names := range codes {
+		unique := map[string]bool{}
+		for _, name := range names {
+			unique[name] = true
+		}
+		if len(unique) < 2 {
+			continue
+		}
+		sorted := make([]string, 0, len(unique))
+		for name := range unique {
+			sorted = append(sorted, name)
+		}
+		sort.Strings(sorted)
+		duplicates = append(duplicates, code+": "+strings.Join(sorted, ", "))
+	}
+	sort.Strings(duplicates)
+
+	assert.Emptyf(t, duplicates, "error codes must be unique across all packages, got duplicates:\n%s", strings.Join(duplicates, "\n"))
+}