service.go

@@ -364,19 +364,25 @@ func (s *Service) Handlers() []KeyHandler {
 //	T("i18n.fail.delete", "file")       // "Failed to delete file"
 func (s *Service) T(messageID string, args ...any) string {
 	s.mu.RLock()
-	defer s.mu.RUnlock()
-	result := RunHandlerChain(s.handlers, messageID, args, func() string {
+	handlers := append([]KeyHandler(nil), s.handlers...)
+	debug := s.debug
+	s.mu.RUnlock()
+
+	result := RunHandlerChain(handlers, messageID, args, func() string {
 		var data any
 		if len(args) > 0 {
 			data = args[0]
 		}
-		text := s.resolveWithFallback(messageID, data)
+
+		s.mu.RLock()
+		text := s.resolveWithFallbackLocked(messageID, data)
+		s.mu.RUnlock()
 		if text == "" {
 			return s.handleMissingKey(messageID, args)
 		}
 		return text
 	})
-	if s.debug {
+	if debug {
 		return debugFormat(messageID, result)
 	}
 	return result
@@ -390,55 +396,55 @@ func (s *Service) Translate(messageID string, args ...any) core.Result {
 
 // resolveDirect performs exact-key lookup in the current language, its base
 // language tag, and then the configured fallback language.
-func (s *Service) resolveDirect(messageID string, data any) string {
-	if text := s.tryResolve(s.currentLang, messageID, data); text != "" {
+func (s *Service) resolveDirectLocked(messageID string, data any) string {
+	if text := s.tryResolveLocked(s.currentLang, messageID, data); text != "" {
 		return text
 	}
 	if base := baseLanguageTag(s.currentLang); base != "" && base != s.currentLang {
-		if text := s.tryResolve(base, messageID, data); text != "" {
+		if text := s.tryResolveLocked(base, messageID, data); text != "" {
 			return text
 		}
 	}
-	if text := s.tryResolve(s.fallbackLang, messageID, data); text != "" {
+	if text := s.tryResolveLocked(s.fallbackLang, messageID, data); text != "" {
 		return text
 	}
 	if base := baseLanguageTag(s.fallbackLang); base != "" && base != s.fallbackLang {
-		return s.tryResolve(base, messageID, data)
+		return s.tryResolveLocked(base, messageID, data)
 	}
 	return ""
 }
 
-func (s *Service) resolveWithFallback(messageID string, data any) string {
-	if text := s.resolveDirect(messageID, data); text != "" {
+func (s *Service) resolveWithFallbackLocked(messageID string, data any) string {
+	if text := s.resolveDirectLocked(messageID, data); text != "" {
 		return text
 	}
 	if core.Contains(messageID, ".") {
 		parts := core.Split(messageID, ".")
 		verb := parts[len(parts)-1]
 		commonKey := "common.action." + verb
-		if text := s.resolveDirect(commonKey, data); text != "" {
+		if text := s.resolveDirectLocked(commonKey, data); text != "" {
 			return text
 		}
 		commonKey = "common." + verb
-		if text := s.resolveDirect(commonKey, data); text != "" {
+		if text := s.resolveDirectLocked(commonKey, data); text != "" {
 			return text
 		}
 	}
 	return ""
 }
 
-func (s *Service) tryResolve(lang, key string, data any) string {
+func (s *Service) tryResolveLocked(lang, key string, data any) string {
 	context, gender, location, formality := s.getEffectiveContextGenderLocationAndFormality(data)
 	extra := s.getEffectiveContextExtra(data)
 	for _, lookupKey := range lookupVariants(key, context, gender, location, formality, extra) {
-		if text := s.resolveMessage(lang, lookupKey, data); text != "" {
+		if text := s.resolveMessageLocked(lang, lookupKey, data); text != "" {
 			return text
 		}
 	}
 	return ""
 }
 
-func (s *Service) resolveMessage(lang, key string, data any) string {
+func (s *Service) resolveMessageLocked(lang, key string, data any) string {
 	msg, ok := s.getMessage(lang, key)
 	if !ok {
 		return ""
@@ -770,7 +776,7 @@ func (s *Service) Raw(messageID string, args ...any) string {
 	if len(args) > 0 {
 		data = args[0]
 	}
-	text := s.resolveDirect(messageID, data)
+	text := s.resolveDirectLocked(messageID, data)
 	if text == "" {
 		return s.handleMissingKey(messageID, args)
 	}

service_test.go

@@ -3,6 +3,7 @@ package i18n
 import (
 	"testing"
 	"testing/fstest"
+	"time"
 
 	"dappco.re/go/core"
 )
@@ -17,6 +18,21 @@ func (messageBaseFallbackLoader) Load(lang string) (map[string]Message, *Grammar
 	return map[string]Message{}, nil, nil
 }
 
+type serviceMutatingHandler struct {
+	svc *Service
+}
+
+func (h serviceMutatingHandler) Match(key string) bool {
+	return key == "custom.mutate.language"
+}
+
+func (h serviceMutatingHandler) Handle(key string, args []any, next func() string) string {
+	if h.svc != nil {
+		_ = h.svc.SetLanguage("fr")
+	}
+	return "mutated"
+}
+
 func TestNewService(t *testing.T) {
 	svc, err := New()
 	if err != nil {
@@ -218,6 +234,33 @@ func TestServiceRaw(t *testing.T) {
 	}
 }
 
+func TestServiceT_CustomHandlerCanMutateService(t *testing.T) {
+	svc, err := New()
+	if err != nil {
+		t.Fatalf("New() failed: %v", err)
+	}
+
+	svc.PrependHandler(serviceMutatingHandler{svc: svc})
+
+	done := make(chan string, 1)
+	go func() {
+		done <- svc.T("custom.mutate.language")
+	}()
+
+	select {
+	case got := <-done:
+		if got != "mutated" {
+			t.Fatalf("T(custom.mutate.language) = %q, want %q", got, "mutated")
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("T(custom.mutate.language) timed out while handler mutated service state")
+	}
+
+	if got := svc.Language(); got != "fr" {
+		t.Fatalf("Language() = %q, want %q", got, "fr")
+	}
+}
+
 func TestServiceRaw_DoesNotUseCommonFallbacks(t *testing.T) {
 	svc, err := New()
 	if err != nil {