Merge pull request #2263 from jimklimov/issue-build-without-usb

Fix builds `--without-usb`

NEWS.adoc

@@ -74,6 +74,8 @@ https://github.com/networkupstools/nut/milestone/10
    * Set the `DesktopFileName` in `scripts/python/app/NUT-Monitor-py3qt5`,
      this binds the application with the desktop file and allow the Desktop
      implementation to display the proper icon and application name. [#2205]
+   * Original recipe for `apc_modbus` strictly required USB support even if
+     building NUT without it. [#2262]
 
  - nut-usbinfo.pl, nut-scanner and libnutscan:
    * USB VendorID:ProductID support list files generated by the script for

drivers/Makefile.am

@@ -303,8 +303,16 @@ generic_modbus_SOURCES = generic_modbus.c
 generic_modbus_LDADD = $(LDADD_DRIVERS) $(LIBMODBUS_LIBS)
 adelsystem_cbi_SOURCES = adelsystem_cbi.c
 adelsystem_cbi_LDADD = $(LDADD_DRIVERS) $(LIBMODBUS_LIBS)
-apc_modbus_SOURCES = apc_modbus.c $(LIBUSB_IMPL) hidparser.c usb-common.c
-apc_modbus_LDADD = $(LDADD_DRIVERS) $(LIBMODBUS_LIBS) $(LIBUSB_LIBS)
+
+# APC Modbus driver (with support of modbus over different media)
+# Note that a version of libmodbus built with USB support is also needed
+# for USB connections. Legacy versions work for Serial and TCP links.
+apc_modbus_SOURCES = apc_modbus.c
+apc_modbus_LDADD = $(LDADD_DRIVERS) $(LIBMODBUS_LIBS)
+if WITH_USB
+  apc_modbus_SOURCES += $(LIBUSB_IMPL) hidparser.c usb-common.c
+  apc_modbus_LDADD += $(LIBUSB_LIBS)
+endif
 
 # Huawei UPS2000 driver
 # (this is both a Modbus and a serial driver)