bug#18926: cmake-build-system should set CMAKE_INSTALL_LIBDIR and CMAKE_PREFIX_PATH

[ludo@gnu.org (Ludovic Courtès)]

宋文武 <iyzsong@gmail.com> skribis:

> Ludovic Courtès <ludo@gnu.org> writes:
>
>> 宋文武 <iyzsong@gmail.com> skribis:
>>
>>> Ludovic Courtès <ludo@gnu.org> writes:
>>>
>>>> 宋文武 <iyzsong@gmail.com> skribis:
>>>>
>>>>> if CMAKE_INSTALL_LIBDIR not set to `lib`, GNUInstallDirs.cmake will install
>>>>> libraries files to $out/lib64.
>>>>
>>>> I found several CMake-built libraries on x86_64 (graphite2, openjpeg,
>>>> qjson) that all use lib/, not lib64/.
>>>>
>>>> Then I found one counterexample, libftdi; however, setting
>>>> CMAKE_INSTALL_LIBDIR=lib doesn’t make any different: it still installs
>>>> libraries in $out/lib64.  Any idea?
>>> libftdi (not using GNUInstallDirs.cmake) handle this itself by
>>> set LIB_SUFFIX, look like we have to set it specifically.
>>
>> Ah, OK.
>>
>> Still, graphite2, openjpeg, and qjson all install to $prefix/lib, even
>> when not passing CMAKE_INSTALL_LIBDIR=lib.  Is it really needed?
> Not sure, it's just for packages using GNUInstallDirs.cmake.
>>
>>>>> if CMAKE_PREFIX_PATH not set to PATH of `inputs`, cmake will unable to
>>>>> find cmake modules of inputs.
>>>>
>>>> You’re talking about .cmake files, right?
>>> yes, but now I find out that they can under both lib/cmake and share/cmake.
>>
>> In that case...
>>
>>>> +      ;; Search path used by 'FIND_PACKAGE' and 'INCLUDE'.
>>>> +      (search-path-specification
>>>> +       (variable "CMAKE_MODULE_PATH")
>>>> +       (directories '("lib/cmake")))))
>>                                     ^
>> ... just add "share/cmake" here. ---’
>>
>> Could you try that?
> Well, it not work, here is the exact output by liblxqt:

[...]

>>> after add CMAKE_PREFIX_PATH with:
>>>
>>>   (search-path-specification
>>>     (variable "CMAKE_PREFIX_PATH")
>>>     (directories '("")))
>>
>> I thought about it, but that "" is inelegant and not as clear.
> Yes, it not feeling good, but I have no better idea now.

In ‘core-updates’ it’s now possible to specify file patterns, so we
could look for *.cmake files under lib/cmake or share/cmake like this:

  (search-path-specification
    (variable "CMAKE_MODULE_PATH")
    (files '("lib/cmake" "share/cmake"))
    (file-type 'regular)
    (file-pattern "\\.cmake$"))

Would it help?  What else is needed?

Ludo’.