[CMake] "Pre-configure" step in CMake

[Tamás Kenéz]

What if you call your dependency-fetcher script with a straight
macro/function call or `include` or `execute_process` instead of putting it
into a custom target? I'm thinking of something like this:

    set(DEP_SCRIPT_OUT ${CMAKE_CURRENT_BINARY_DIR}/dep-script-out.cmake)
    if(NOT EXISTS "${DEP_SCRIPT_OUT}")
      execute_process(${CMAKE_COMMAND}
        -DC_COMPILER_ID=${CMAKE_C_COMPILER_ID}
        -DC_COMPILER_VERSION=${CMAKE_C_COMPILER_VERSION}
        -DDEP_SCRIPT_OUT =${DEP_SCRIPT_OUT}
        -P dependency-fetcher.cmake)
    endif()
    include(${DEP_SCRIPT_OUT})

or, simply:

    if(NOT DEPENDENCIES_FETCHED)
      include(dependency-fetcher.cmake)
      # fetch_dependencies() # call it in case it's implemented as a
macro/function
      set(DEPENDENCIES_FETCHED ON CACHE BOOL "" FORCE)
    endif()

In the latter case there's no need to write the variables into a script
since the fetcher runs in the same scope.

Tamas


On Wed, Sep 23, 2015 at 9:49 PM, Matthäus G. Chajdas <cmake at anteru.net>
wrote:

> Hi,
>
> I'm trying to solve the following the problem: I have a C++ application
> and a dependency fetching script. I want to simplify the initial build
> such that the following happens: On the first run of cmake, the compiler
> ID and version is passed to an external script, which fetches some
> pre-build binaries. It then writes a CMake file which contains basically
> only set(FOO_INCLUDE_DIR /dep-dir), set(FOO_LIBRARY_DIR /dep-dir)
> commands. CMake would then read this file and subsequent find_library
> calls would pick up the values from this new CMake file. The idea is
> that "actual" build is dependent on this first dependency step, but it's
> already within the CMake framework so I can grab the compiler info and
> other build info.
>
> The obvious problem is that while I can easily run the external script
> by using configure_file, and have a custom target that does the
> dependency fetching and CMake configure file generation. But I don't see
> an easy way to get CMake to make the "rest of the project" depend on
> that configure file. How can I make such a "two-stage" build with CMake?
>
> Cheers,
>   Matthäus
> --
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