stubs: be smarter about the library error messages

Detect the common case of users cloning the core with the original name
"ArduinoCore-zephyr" and warn them about it, as it causes library
detection issues.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Author: pillo79

libraries/stubs/Arduino_RouterBridge.h

@@ -7,10 +7,31 @@
 #pragma once
 
 /*
- * This is just a placeholder to handle the case of the Arduino_RouterBridge
- * library NOT being installed. If this file is chosen, the actual library is
- * missing and the user needs to be warned about it.
+ * This file is used to detect issues with the Arduino_RouterBridge library not
+ * being detected properly. If this gets selected, either the library is not
+ * installed or there is an issue with the library detection.
+ */
+
+#ifdef ARDUINO_ARCH_ARDUINOCORE_ZEPHYR
+
+/* 
+ * The core was probably cloned with the original name in the hardware/ sketch
+ * folder, but that becomes part of the FQBN and it messes with library search,
+ * so even if the library is installed it is deemed "not compatible".
+ * Force the user to rename the core folder to "zephyr" to avoid this issue.
+ */
+
+#error                                                                                             \
+	"Invalid configuration: please rename your 'ArduinoCore-zephyr' folder inside hardware/ to 'zephyr'."
+
+#else
+
+/*
+ * If the folder name is correct, then the actual library is really missing and
+ * the user needs to be warned about it.
  */
 
 #error                                                                                             \
 	"Please install the Arduino_RouterBridge library from the Library Manager for proper Serial support on this board."
+
+#endif