[CMake] Imported libraries and cyclic dependencies

[Rainer Poisel]

Hi,

I am having troubles with linking a bunch of imported libraries that
have cyclic dependencies.

This is what I am doing:

8<=======================
find_library(ESP8266_SDK_LIB_MAIN main ${ESP8266_SDK_BASE}/lib)
add_library(esp8266_main UNKNOWN IMPORTED)
set_property(TARGET esp8266_main PROPERTY IMPORTED_LOCATION
"${ESP8266_SDK_LIB_MAIN}")

find_library(ESP8266_SDK_LIB_PHY phy ${ESP8266_SDK_BASE}/lib)
add_library(esp8266_phy UNKNOWN IMPORTED)
set_property(TARGET esp8266_phy PROPERTY IMPORTED_LOCATION
"${ESP8266_SDK_LIB_PHY}")

find_library(ESP8266_SDK_LIB_PP pp ${ESP8266_SDK_BASE}/lib)
add_library(esp8266_pp UNKNOWN IMPORTED)
set_property(TARGET esp8266_pp PROPERTY IMPORTED_LOCATION
"${ESP8266_SDK_LIB_PP}")

find_library(ESP8266_SDK_LIB_LWIP lwip ${ESP8266_SDK_BASE}/lib)
add_library(esp8266_lwip UNKNOWN IMPORTED)
set_property(TARGET esp8266_lwip PROPERTY IMPORTED_LOCATION
"${ESP8266_SDK_LIB_LWIP}")

target_link_libraries(ESP8266_SDK INTERFACE
    gcc
    esp8266_lwip
    esp8266_main
    esp8266_phy
    esp8266_pp
)

target_link_libraries(esp8266_main INTERFACE
    esp8266_lwip
    esp8266_pp
    esp8266_phy
)
8<=======================

The given example is not complete. However, I hope it is sufficient to
give you an idea of what I want to achieve: I would like to specify
the dependencies between imported libraries. Subsequently I want to
make the linker call mention my libraries several times in order to
make the linker resolve all dependency cycles (multiplicity).

This is the corresponding error message:

8<=======================
CMake Error at external/esp8266-cmake/sdk/nonos-1.4.0.cmake:111
(target_link_libraries):
Cannot specify link libraries for target "esp8266_main" which is not built
by this project.
8<=======================

As a workaround I added the -Wl,--start-group (referred to as
BUILD_LINK_PREFIX) and the -Wl,--end-group (referred to as
BUILD_LINK_SUFFIX) arguments (yes, it is a GCC) directly to the
invocation of target_link_libraries() of my executable which has been
defined by add_executable() beforehand. But I think that this is just
a botch-up.

Here is an example of the complete code (using the before-mentioned workaround):
  * https://github.com/rpoisel/esp8266-mqtt
  * https://github.com/rpoisel/esp8266-cmake/blob/master/main/CMakeLists.txt

Thanks for any suggestions in advance,
  Rainer