fix(go/ai): genkit ignores dotprompt-defined roles (#3780)

Author: josearomeroj

go/ai/prompt.go

@@ -624,7 +624,54 @@ func LoadPrompt(r api.Registry, dir, filename, namespace string) Prompt {
 	}
 
 	key := promptKey(name, variant, namespace)
-	prompt := DefinePrompt(r, key, opts, WithPrompt(parsedPrompt.Template))
+
+	dpMessages, err := dotprompt.ToMessages(parsedPrompt.Template, &dotprompt.DataArgument{})
+	if err != nil {
+		slog.Error("Failed to convert prompt template to messages", "file", sourceFile, "error", err)
+		return nil
+	}
+
+	var systemText string
+	var nonSystemMessages []*Message
+	for _, dpMsg := range dpMessages {
+		parts, err := convertToPartPointers(dpMsg.Content)
+		if err != nil {
+			slog.Error("Failed to convert message parts", "file", sourceFile, "error", err)
+			return nil
+		}
+
+		role := Role(dpMsg.Role)
+		if role == RoleSystem {
+			var textParts []string
+			for _, part := range parts {
+				if part.IsText() {
+					textParts = append(textParts, part.Text)
+				}
+			}
+
+			if len(textParts) > 0 {
+				systemText = strings.Join(textParts, " ")
+			}
+		} else {
+			nonSystemMessages = append(nonSystemMessages, &Message{Role: role, Content: parts})
+		}
+	}
+
+	promptOpts := []PromptOption{opts}
+
+	// Add system prompt if found
+	if systemText != "" {
+		promptOpts = append(promptOpts, WithSystem(systemText))
+	}
+
+	// If there are non-system messages, use WithMessages, otherwise use WithPrompt for template
+	if len(nonSystemMessages) > 0 {
+		promptOpts = append(promptOpts, WithMessages(nonSystemMessages...))
+	} else if systemText == "" {
+		promptOpts = append(promptOpts, WithPrompt(parsedPrompt.Template))
+	}
+
+	prompt := DefinePrompt(r, key, promptOpts...)
 
 	slog.Debug("Registered Dotprompt", "name", key, "file", sourceFile)
 

go/ai/prompt_test.go

@@ -1148,3 +1148,64 @@ Hello!
 		t.Fatalf("Failed to execute prompt: %v", err)
 	}
 }
+
+func TestMultiMessagesRenderPrompt(t *testing.T) {
+	tempDir := t.TempDir()
+
+	mockPromptFile := filepath.Join(tempDir, "example.prompt")
+	mockPromptContent := `---
+model: test/chat
+description: A test prompt
+---
+<<<dotprompt:role:system>>>
+You are a pirate!
+
+<<<dotprompt:role:user>>>
+Hello!
+`
+
+	if err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0644); err != nil {
+		t.Fatalf("Failed to create mock prompt file: %v", err)
+	}
+
+	prompt := LoadPrompt(registry.New(), tempDir, "example.prompt", "multi-namespace-roles")
+
+	actionOpts, err := prompt.Render(context.Background(), map[string]any{})
+	if err != nil {
+		t.Fatalf("Failed to execute prompt: %v", err)
+	}
+
+	// Check that actionOpts is not nil
+	if actionOpts == nil {
+		t.Fatal("Expected actionOpts to be non-nil")
+	}
+
+	// Check that we have exactly 2 messages (system and user)
+	if len(actionOpts.Messages) != 2 {
+		t.Fatalf("Expected 2 messages, got %d", len(actionOpts.Messages))
+	}
+
+	// Check first message (system role)
+	systemMsg := actionOpts.Messages[0]
+	if systemMsg.Role != RoleSystem {
+		t.Errorf("Expected first message role to be 'system', got '%s'", systemMsg.Role)
+	}
+	if len(systemMsg.Content) == 0 {
+		t.Fatal("Expected system message to have content")
+	}
+	if strings.TrimSpace(systemMsg.Content[0].Text) != "You are a pirate!" {
+		t.Errorf("Expected system message text to be 'You are a pirate!', got '%s'", systemMsg.Content[0].Text)
+	}
+
+	// Check second message (user role)
+	userMsg := actionOpts.Messages[1]
+	if userMsg.Role != RoleUser {
+		t.Errorf("Expected second message role to be 'user', got '%s'", userMsg.Role)
+	}
+	if len(userMsg.Content) == 0 {
+		t.Fatal("Expected user message to have content")
+	}
+	if strings.TrimSpace(userMsg.Content[0].Text) != "Hello!" {
+		t.Errorf("Expected user message text to be 'Hello!', got '%s'", userMsg.Content[0].Text)
+	}
+}