add warn on bad template

Author: ngxson

examples/main/main.cpp

@@ -207,14 +207,17 @@ int main(int argc, char ** argv) {
     }
 
     // auto enable conversation mode if chat template is available
-    if (
-        params.conversation_mode == COMMON_CONVERSATION_MODE_AUTO
-        && (!common_get_builtin_chat_template(model).empty() || !params.chat_template.empty())
-    ) {
+    const bool has_chat_template = !common_get_builtin_chat_template(model).empty() || !params.chat_template.empty();
+    if (params.conversation_mode == COMMON_CONVERSATION_MODE_AUTO && has_chat_template) {
         LOG_INF("%s: chat template is available, enabling conversation mode (disable it with -no-cnv)\n", __func__);
         params.conversation_mode = COMMON_CONVERSATION_MODE_ENABLED;
     }
 
+    // in case user force-activate conversation mode (via -cnv) without proper chat template, we show a warning
+    if (params.conversation_mode && !has_chat_template) {
+        LOG_WRN("%s: chat template is not available or is not supported. This may cause the model to output suboptimal responses\n", __func__);
+    }
+
     // print chat template example in conversation mode
     if (params.conversation_mode) {
         if (params.enable_chat_template) {