[CMake] find_package to find Cygwin versions of Flex and Bison in Windows

[Eric Doenges]

You can prepend C:\cygwin64\bin to the CMAKE_PROGRAM_PATH variable so 
that it looks there first.  While the find_package documentation does 
not mention CMAKE_PROGRAM_PATH, I know this works for bison and flex 
because that is what we do in our project (presumably, find_program is 
used internally within the find_package, explaining why 
CMAKE_PROGRAM_PATH is considered).

You could also try setting the FLEX_ROOT and BISON_ROOT variables to 
C:\cygwin64\bin or perhaps C:\cygwin64. According to the find_package 
documentation, this should allow you to set the search location on a 
per-package basis. However, I have not had this work for me, so your 
mileage may vary.

Am 05.03.20 um 12:12 schrieb Stephen Morris:
> To compile my application I need to use the Flex and Bison applications. To compile under Linux, all I need to do in my CMakeLists.txt file to find them is
>
>      find_package(FLEX REQUIRED)
>      find_package(BISON REQUIRED)
>
> ...and everything works as expected.
>
> In Windows, however, I'm using the Cygwin versions of Flex and Bison which are installed in C:\cygwin64\bin. This doesn't seem to be on the path that find_package searches in Module Mode, so the search returns unsuccessfully.
>
> However, if I try to tell find_package where to look, viz.
>
>      find_package(FLEX REQUIRED PATHS C:/cygwin64/bin NO_DEFAULT_PATH)
>      find_package(BISON REQUIRED PATHS C:/cygwin64/bin NO_DEFAULT_PATH)
>
> ...then by adding the PATHS keyword I've invoked Config mode and I get an error message saying:
>
>      Could not find a package configuration file provided by "FLEX" with any of
>      the following names
>
>          FLEXConfig.cmake
>          flex-config.cmake
>
> ...because sure enough Cygwin does not provide these files.
>
> So what can I do? Ideally I'd like to use Module Mode but provide a path hint; but there seems no way to do that.
>
> At the moment I can only think of:
> (a) Hard-coding add_custom_target commands to invoke flex and bison entirely manually when they're needed, or
> (b) Writing my own FLEXConfig.cmake and BISONConfig.cmake files for use in Config Mode.
>
> Both of these seem disproportionately difficult for what seems to me like it ought to be a common and simple problem. So is there a better solution that I'm missing?
>
*Dr. Eric Dönges*
Senior Software Engineer

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