[CMake] [cmake-developers] Debugging find_package() search behavior?

[Robert Dailey]

Thanks for your help, the problem is that I was expecting too much
consistency between find module behavior. I'll treat them as if I have
no guarantees.

Last question: Are there guarantees with find modules and
CMAKE_FIND_ROOT_PATH? I'm asking because on Android, when I use
find_package(), behavior is different because the NDK's toolchain file
sets:

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
list(APPEND CMAKE_FIND_ROOT_PATH "${ANDROID_NDK}")

To try to "intercept" the search of NDK for libraries using
find_package(), I try this:

set( CMAKE_FIND_ROOT_PATH ${ZIOSK_THIRD_PARTY_INSTALL} ${CMAKE_FIND_ROOT_PATH} )

However, after running, it's always finding results in the NDK
directory set by the toolchain file, even though I put mine first in
the list. Furthermore, my install of zlib has the correct version, the
NDK one does not, but it still says it founds the NDK version.

On Tue, Aug 29, 2017 at 10:33 AM, David Cole <DLRdave at aol.com> wrote:
> That's correct:
>
> find modules do what they want, and most do not pay attention to
> CMAKE_PREFIX_PATH.
>
> It's better to use a config file, but when you have to use a find
> module, you have to dig in and figure out the right way to use each
> one.
>
>
>
> On Tue, Aug 29, 2017 at 11:25 AM, Robert Dailey
> <rcdailey.lists at gmail.com> wrote:
>> I think the discrepancy here might be config vs module find mode. The
>> documentation I linked seems to be for config mode only, however I'm
>> utilizing the CMake-shipped FindZLIB.cmake module to find this
>> particular library. Does this offer no guarantees on how
>> CMAKE_PREFIX_PATH is used?
>>
>> On Tue, Aug 29, 2017 at 10:11 AM, Robert Dailey
>> <rcdailey.lists at gmail.com> wrote:
>>> What I'm hoping for is that find_package() follows the rules it
>>> documents here:
>>> https://cmake.org/cmake/help/v3.6/command/find_package.html
>>>
>>> Specifically, it states it searches these paths (and that <name> is
>>> treated case-insensitive):
>>>
>>> <prefix>/                                               (W)
>>> <prefix>/(cmake|CMake)/                                 (W)
>>> <prefix>/<name>*/                                       (W)
>>> <prefix>/<name>*/(cmake|CMake)/                         (W)
>>> <prefix>/(lib/<arch>|lib|share)/cmake/<name>*/          (U)
>>> <prefix>/(lib/<arch>|lib|share)/<name>*/                (U)
>>> <prefix>/(lib/<arch>|lib|share)/<name>*/(cmake|CMake)/  (U)
>>>
>>> If this is true, then the 3rd one from the top should be a match,
>>> because <prefix> is set to:
>>>
>>> E:/code/frontend/msvc_2015/third_party/installed
>>>
>>> And <name> is set to ZLIB in find_package() first argument, so it
>>> should be adding that to the end.
>>>
>>> I need to keep CMAKE_PREFIX_PATH pointing to the parent directory
>>> ("installed") because I have other libraries that get installed in
>>> that directory, each with their own directory to contain their
>>> installation files. If find_package() is appending <name> to <prefix>
>>> like it says it should, it should find each one of them without
>>> switching the value of CMAKE_PREFIX_PATH.
>>>
>>> Am I misunderstanding something?
>>>
>>>
>>> On Tue, Aug 29, 2017 at 10:06 AM, David Cole <DLRdave at aol.com> wrote:
>>>> Shouldn't the "/zlib" at the end be included in your CMAKE_PREFIX_PATH?
>>>>
>>>> On Tue, Aug 29, 2017 at 11:01 AM, Robert Dailey
>>>> <rcdailey.lists at gmail.com> wrote:
>>>>> On Tue, Aug 29, 2017 at 9:56 AM, Brad King <brad.king at kitware.com> wrote:
>>>>>> On 08/29/2017 10:55 AM, Brad King wrote:
>>>>>>> On 08/29/2017 10:48 AM, Robert Dailey wrote:
>>>>>>>> CMAKE_PREFIX_PATH: E:/code/frontend/msvc_2015/third_party/installed
>>>>>>>> CMAKE_FIND_ROOT_PATH: E:/code/frontend/msvc_2015/third_party/installed
>>>>>>>
>>>>>>> I'm not sure how CMAKE_FIND_ROOT_PATH's path re-rooting interacts with
>>>>>>> drive letters on Windows.
>>>>>>
>>>>>> Oops, sent too soon.
>>>>>>
>>>>>> CMAKE_FIND_ROOT_PATH should not be necessary here.  It's for cross-compiling
>>>>>> to re-root paths like `/usr` into some prefix on the host.
>>>>>>
>>>>>> -Brad
>>>>>
>>>>> Ok but even if I remove that, find_package() still isn't working......
>>>>> --
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