Allow for `get_hardware_id()` to be used for serial number. (#24053)

* Allow for `get_hardware_id()` to be used for serial number.

* Length checks.

* Explain length.

* Cleanup.

* Preprocessor magic.

* Use the force, Batman.

* Swap logic; if SERIAL_NUMBER is defined use that, otherwise derive it.

* Cleanup.

* Cleanup.

platforms/chibios/config.h

···
 #ifndef CORTEX_ENABLE_WFI_IDLE
 #    define CORTEX_ENABLE_WFI_IDLE TRUE
 #endif // CORTEX_ENABLE_WFI_IDLE
+
+#ifndef SERIAL_NUMBER_USE_HARDWARE_ID
+#    define SERIAL_NUMBER_USE_HARDWARE_ID TRUE
+#endif // SERIAL_NUMBER_USE_HARDWARE_ID

tmk_core/protocol/usb_descriptor.c

···
 #    include "os_detection.h"
 #endif
 
+#if defined(SERIAL_NUMBER) || (defined(SERIAL_NUMBER_USE_HARDWARE_ID) && SERIAL_NUMBER_USE_HARDWARE_ID == TRUE)
+
+#    define HAS_SERIAL_NUMBER
+
+#    if defined(SERIAL_NUMBER_USE_HARDWARE_ID) && SERIAL_NUMBER_USE_HARDWARE_ID == TRUE
+#        include "hardware_id.h"
+#    endif
+
+#endif // defined(SERIAL_NUMBER) || (defined(SERIAL_NUMBER_USE_HARDWARE_ID) && SERIAL_NUMBER_USE_HARDWARE_ID == TRUE)
+
 // clang-format off
 
 /*
···
     .ReleaseNumber              = DEVICE_VER,
     .ManufacturerStrIndex       = 0x01,
     .ProductStrIndex            = 0x02,
-#if defined(SERIAL_NUMBER)
+#ifdef HAS_SERIAL_NUMBER
     .SerialNumStrIndex          = 0x03,
-#else
+#else // HAS_SERIAL_NUMBER
     .SerialNumStrIndex          = 0x00,
-#endif
+#endif // HAS_SERIAL_NUMBER
     .NumberOfConfigurations     = FIXED_NUM_CONFIGURATIONS
 };
 
···
 /*
  * String descriptors
  */
+
+#define USB_DESCRIPTOR_SIZE_LITERAL_U16STRING(str) \
+    (sizeof(USB_Descriptor_Header_t) + sizeof(str) - sizeof(wchar_t)) // include header, don't count null terminator
+
 const USB_Descriptor_String_t PROGMEM LanguageString = {
     .Header = {
-        .Size                   = 4,
+        .Size                   = sizeof(USB_Descriptor_Header_t) + sizeof(uint16_t),
         .Type                   = DTYPE_String
     },
     .UnicodeString              = {LANGUAGE_ID_ENG}
···
 
 const USB_Descriptor_String_t PROGMEM ManufacturerString = {
     .Header = {
-        .Size                   = sizeof(USBSTR(MANUFACTURER)),
+        .Size                   = USB_DESCRIPTOR_SIZE_LITERAL_U16STRING(USBSTR(MANUFACTURER)),
         .Type                   = DTYPE_String
     },
     .UnicodeString              = USBSTR(MANUFACTURER)
···
 
 const USB_Descriptor_String_t PROGMEM ProductString = {
     .Header = {
-        .Size                   = sizeof(USBSTR(PRODUCT)),
+        .Size                   = USB_DESCRIPTOR_SIZE_LITERAL_U16STRING(USBSTR(PRODUCT)),
         .Type                   = DTYPE_String
     },
     .UnicodeString              = USBSTR(PRODUCT)
 };
 
+// clang-format on
+
 #if defined(SERIAL_NUMBER)
+// clang-format off
 const USB_Descriptor_String_t PROGMEM SerialNumberString = {
     .Header = {
-        .Size                   = sizeof(USBSTR(SERIAL_NUMBER)),
+        .Size                   = USB_DESCRIPTOR_SIZE_LITERAL_U16STRING(USBSTR(SERIAL_NUMBER)),
         .Type                   = DTYPE_String
     },
     .UnicodeString              = USBSTR(SERIAL_NUMBER)
 };
-#endif
+// clang-format on
+
+#else // defined(SERIAL_NUMBER)
+
+#    if defined(SERIAL_NUMBER_USE_HARDWARE_ID) && SERIAL_NUMBER_USE_HARDWARE_ID == TRUE
+
+#        if defined(__AVR__)
+#            error Dynamically setting the serial number on AVR is unsupported as LUFA requires the string to be in PROGMEM.
+#        endif // defined(__AVR__)
+
+#        ifndef SERIAL_NUMBER_LENGTH
+#            define SERIAL_NUMBER_LENGTH (sizeof(hardware_id_t) * 2)
+#        endif
+
+#        define SERIAL_NUMBER_DESCRIPTOR_SIZE                                            \
+            (sizeof(USB_Descriptor_Header_t)                     /* Descriptor header */ \
+             + (((SERIAL_NUMBER_LENGTH) + 1) * sizeof(wchar_t))) /* Length of serial number, with potential extra character as we're converting 2 nibbles at a time */
+
+uint8_t SerialNumberString[SERIAL_NUMBER_DESCRIPTOR_SIZE] = {0};
+
+void set_serial_number_descriptor(void) {
+    static bool is_set = false;
+    if (is_set) {
+        return;
+    }
+    is_set = true;
 
-// clang-format on
+    static const char        hex_str[] = "0123456789ABCDEF";
+    hardware_id_t            id        = get_hardware_id();
+    USB_Descriptor_String_t* desc      = (USB_Descriptor_String_t*)SerialNumberString;
+
+    // Copy across nibbles from the hardware ID as unicode hex characters
+    int      length = MIN(sizeof(id) * 2, SERIAL_NUMBER_LENGTH);
+    uint8_t* p      = (uint8_t*)&id;
+    for (int i = 0; i < length; i += 2) {
+        desc->UnicodeString[i + 0] = hex_str[p[i / 2] >> 4];
+        desc->UnicodeString[i + 1] = hex_str[p[i / 2] & 0xF];
+    }
+
+    desc->Header.Size = sizeof(USB_Descriptor_Header_t) + (length * sizeof(wchar_t)); // includes header, don't count null terminator
+    desc->Header.Type = DTYPE_String;
+}
+
+#    endif // defined(SERIAL_NUMBER_USE_HARDWARE_ID) && SERIAL_NUMBER_USE_HARDWARE_ID == TRUE
+
+#endif // defined(SERIAL_NUMBER)
 
 /**
  * This function is called by the library when in device mode, and must be overridden (see library "USB Descriptors"
···
                     Size    = pgm_read_byte(&ProductString.Header.Size);
 
                     break;
-#if defined(SERIAL_NUMBER)
+#ifdef HAS_SERIAL_NUMBER
                 case 0x03:
-                    Address = &SerialNumberString;
-                    Size    = pgm_read_byte(&SerialNumberString.Header.Size);
+                    Address = (const USB_Descriptor_String_t*)&SerialNumberString;
+#    if defined(SERIAL_NUMBER)
+                    Size = pgm_read_byte(&SerialNumberString.Header.Size);
+#    else
+                    set_serial_number_descriptor();
+                    Size = ((const USB_Descriptor_String_t*)SerialNumberString)->Header.Size;
+#    endif
 
                     break;
-#endif
+#endif // HAS_SERIAL_NUMBER
             }
 #ifdef OS_DETECTION_ENABLE
             process_wlength(wLength);