refactor(lwip): Added on/off switch for LwIP stack

* This switch allows applications to replace lwip with a different
  IP stack or just make it build if it is a dependency but not
  actually needed.

components/esp-tls/CMakeLists.txt

@@ -35,7 +35,7 @@ set_property(TARGET ${lwip} APPEND PROPERTY LINK_INTERFACE_MULTIPLICITY 5)
 else()
     # Check if LWIP in the build for linux target to adapt esp-tls compatibility layer
     idf_build_get_property(build_components BUILD_COMPONENTS)
-    if("lwip" IN_LIST build_components)
+    if(CONFIG_LWIP_ENABLE)
         target_compile_definitions(${COMPONENT_LIB} PRIVATE ESP_TLS_WITH_LWIP=1)
     endif()
 endif()

components/lwip/CMakeLists.txt

@@ -1,4 +1,6 @@
 idf_build_get_property(target IDF_TARGET)
+
+if(CONFIG_LWIP_ENABLE)
     if(NOT ${target} STREQUAL "linux")
         # ESP platform targets share the same port folder
         set(target esp32xx)
@@ -136,7 +138,6 @@ endif()
 
     if(NOT ${target} STREQUAL "linux")
         # Support for vfs and linker fragments only for target builds
-    set(priv_requires vfs)
         set(linker_fragments linker.lf)
         if(CONFIG_VFS_SUPPORT_IO)
             list(APPEND srcs "port/${target}/vfs_lwip.c")
@@ -162,12 +163,18 @@ endif()
     if(CONFIG_LWIP_DHCP_RESTORE_LAST_IP)
         list(APPEND srcs "port/esp32xx/netif/dhcp_state.c")
     endif()
+endif() # CONFIG_LWIP_ENABLE
+
+if(NOT ${target} STREQUAL "linux")
+    set(priv_requires vfs)
+endif()
 
 idf_component_register(SRCS "${srcs}"
                     INCLUDE_DIRS  ${include_dirs}
                     LDFRAGMENTS   ${linker_fragments}
                     PRIV_REQUIRES ${priv_requires})
 
+if(CONFIG_LWIP_ENABLE)
     # lots of LWIP source files evaluate macros that check address of stack variables
     target_compile_options(${COMPONENT_LIB} PRIVATE -Wno-address)
     target_compile_definitions(${COMPONENT_LIB} PRIVATE ESP_LWIP_COMPONENT_BUILD)
@@ -218,3 +225,4 @@ if(${target} STREQUAL "linux")
                     target_link_libraries(${COMPONENT_LIB} INTERFACE "-u __wrap_${wrap}")
         endforeach()
     endif()
+endif()

components/lwip/Kconfig

@@ -1,4 +1,15 @@
 menu "LWIP"
+    config LWIP_ENABLE
+        bool "Enable LwIP stack"
+        default y if !IDF_TARGET_LINUX
+        default n if IDF_TARGET_LINUX
+        help
+            Builds normally if selected. Excludes LwIP from build if unselected, even if it is a
+            dependency of a component or application.
+            Some applications can switch their IP stacks, e.g., when switching between chip
+            and Linux targets (LwIP stack vs. Linux IP stack). Since the LwIP dependency cannot
+            easily be excluded based on a Kconfig option, it has to be a dependency in all cases.
+            This switch allows the LwIP stack to be built selectively, even if it is a dependency.
 
     config LWIP_LOCAL_HOSTNAME
         string "Local netif hostname"

components/mbedtls/CMakeLists.txt

@@ -134,8 +134,7 @@ endif()
 
 # net_sockets.c should only be compiled if BSD socket functions are available.
 # Do this by checking if lwip component is included into the build.
-idf_build_get_property(build_components BUILD_COMPONENTS)
-if(lwip IN_LIST build_components)
+if(CONFIG_LWIP_ENABLE)
     list(APPEND mbedtls_target_sources "${COMPONENT_DIR}/port/net_sockets.c")
     idf_component_get_property(lwip_lib lwip COMPONENT_LIB)
     target_link_libraries(${COMPONENT_LIB} ${linkage_type} ${lwip_lib})

examples/protocols/sockets/udp_client/sdkconfig.ci.linux

@@ -1,3 +1,4 @@
 CONFIG_IDF_TARGET="linux"
 CONFIG_EXAMPLE_IPV4_ADDR="127.0.0.1"
 CONFIG_EXAMPLE_CONNECT_LWIP_TAPIF=n
+CONFIG_LWIP_ENABLE=y

examples/protocols/sockets/udp_client/sdkconfig.defaults.linux

@@ -0,0 +1 @@
+CONFIG_LWIP_ENABLE=y