[cmake-developers] [PATCH] Improve FindGIF version detection (fix for issue #16196)

[Brad King]

On 07/12/2016 11:16 PM, Ben Campbell wrote:
> A fix for https://gitlab.kitware.com/cmake/cmake/issues/16196

Thanks!  Here are some comments.

> the pairs of file()/string() 
> commands seem a bit convoluted for extracting strings out of the header 
> file - is there a more idiomatic approach?

You could use a single `file(STRINGS)` call and then use `foreach()` with
the `IN LISTS` mode to iterate through them.  Then use `if(MATCHES)` to
extract the individual parts with the `CMAKE_MATCH_<n>` variables.

> Also, I'm a bit concerned that they are polluting scope by leaking out 
> the GIFMAJ/GIFMIN/GIFREL working variables... how would I improve this?

Prefix the working variables with _GIF_ and then unset() them at the end.

If the version is now expected to work please also update
`Tests/CMakeOnly/AllFindModules/CMakeLists.txt` to check that
a version number is extracted.  In a CMake build tree run
`ctest -R CMakeOnly.AllFindModules -V` to run the test.

Thanks,
-Brad