[PATCH] D112753: [llvm] [Support] Add CURL HTTP Client.

[Dimitry Andric via Phabricator via llvm-commits]

dim added a comment.

In D112753#3180838 <https://reviews.llvm.org/D112753#3180838>, @noajshu wrote:

> Thanks @dim, I have a patch that should fix this D115189 <https://reviews.llvm.org/D115189> 
> Would that solve the breakage on freebsd?

No, as I went back in history to find this commit that introduced the feature. I'm not a cmake expert, but I think the problem lies in the way features are tested in `llvm/cmake/config-ix.cmake`, e.g.:

  if(CURL_FOUND)
    # Check if curl we found is usable; for example, we may have found a 32-bit
    # library on a 64-bit system which would result in a link-time failure.
    cmake_push_check_state()
    list(APPEND CMAKE_REQUIRED_INCLUDES ${CURL_INCLUDE_DIRS})
    list(APPEND CMAKE_REQUIRED_LIBRARIES ${CURL_LIBRARY})
    check_symbol_exists(curl_easy_init curl/curl.h HAVE_CURL)
    cmake_pop_check_state()
    if(LLVM_ENABLE_CURL STREQUAL FORCE_ON AND NOT HAVE_CURL)
      message(FATAL_ERROR "Failed to configure curl")
    endif()
  endif()

As far as I understand it, the `cmake_pop_check_state()` after the checks *restores* the `CMAKE_REQUIRED_INCLUDES` to its previous value, and therefore removes the appended `CURL_INCLUDE_DIRS` value.

Strangely, most of the external library checks go this way, e.g. for libxml just above:

  if(LibXml2_FOUND)
    # Check if libxml2 we found is usable; for example, we may have found a 32-bit
    # library on a 64-bit system which would result in a link-time failure.
    cmake_push_check_state()
    list(APPEND CMAKE_REQUIRED_INCLUDES ${LIBXML2_INCLUDE_DIRS})
    list(APPEND CMAKE_REQUIRED_LIBRARIES ${LIBXML2_LIBRARIES})
    list(APPEND CMAKE_REQUIRED_DEFINITIONS ${LIBXML2_DEFINITIONS})
    check_symbol_exists(xmlReadMemory libxml/xmlreader.h HAVE_LIBXML2)
    cmake_pop_check_state()
    if(LLVM_ENABLE_LIBXML2 STREQUAL FORCE_ON AND NOT HAVE_LIBXML2)
      message(FATAL_ERROR "Failed to configure libxml2")
    endif()
  endif()

I simply don't understand how this can work, if the detected include dirs are not in a system-default location, such as `/usr/include`...


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