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

[Ben Campbell]

A fix for https://gitlab.kitware.com/cmake/cmake/issues/16196

This is my first attempt at doing anything with CMake, so I'd appreciate 
any feedback on my patch! In particular, the pairs of file()/string() 
commands seem a bit convoluted for extracting strings out of the header 
file - is there a more idiomatic approach?
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?


---
  Modules/FindGIF.cmake | 20 ++++++++++++++++++--
  1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/Modules/FindGIF.cmake b/Modules/FindGIF.cmake
index 7bbb8cf..283a299 100644
--- a/Modules/FindGIF.cmake
+++ b/Modules/FindGIF.cmake
@@ -61,7 +61,8 @@ set(GIF_LIBRARIES ${GIF_LIBRARY})
  # to be always " Version 2.0, " in versions 3.x of giflib.
  # In version 4 the member UserData was added to GifFileType, so we 
check for this
  # one.
-# http://giflib.sourcearchive.com/documentation/4.1.4/files.html
+# Versions after 4.1.6 define GIFLIB_MAJOR, GIFLIB_MINOR, and 
GIFLIB_RELEASE
+# see http://giflib.sourceforge.net/gif_lib.html#compatibility
  if(GIF_INCLUDE_DIR)
    include(${CMAKE_CURRENT_LIST_DIR}/CMakePushCheckState.cmake)
    include(${CMAKE_CURRENT_LIST_DIR}/CheckStructHasMember.cmake)
@@ -71,7 +72,22 @@ if(GIF_INCLUDE_DIR)
    set(CMAKE_REQUIRED_INCLUDES "${GIF_INCLUDE_DIR}")
    CHECK_STRUCT_HAS_MEMBER(GifFileType UserData gif_lib.h 
GIF_GifFileType_UserData )
    if(GIF_GifFileType_UserData)
-    set(GIF_VERSION 4)
+    # OK. So we're version 4 or higher. Check for specific version defines
+    file(STRINGS ${GIF_INCLUDE_DIR}/gif_lib.h GIFMAJ REGEX "^[ 
\t]*#define[ \t]+GIFLIB_MAJOR")
+    string(REGEX REPLACE "^.*GIFLIB_MAJOR ([0-9]+).*$" "\\1" GIFMAJ 
${GIFMAJ})
+    # extract minor version
+    file(STRINGS ${GIF_INCLUDE_DIR}/gif_lib.h GIFMIN REGEX "^[ 
\t]*#define[ \t]+GIFLIB_MINOR")
+    string(REGEX REPLACE "^.*GIFLIB_MINOR ([0-9]+).*$" "\\1" GIFMIN 
${GIFMIN})
+    # point release
+    file(STRINGS ${GIF_INCLUDE_DIR}/gif_lib.h GIFREL REGEX "^[ 
\t]*#define[ \t]+GIFLIB_RELEASE")
+    string(REGEX REPLACE "^.*GIFLIB_RELEASE ([0-9]+).*$" "\\1" GIFREL 
${GIFREL})
+    if(GIFMAJ)
+      # yay - got exact version info
+      set(GIF_VERSION ${GIFMAJ}.${GIFMIN}.${GIFREL})
+    else(GIFMAJ)
+      # couldn't find the defines - assume version 4
+      set(GIF_VERSION 4)
+    endif(GIFMAJ)
    endif()
    CMAKE_POP_CHECK_STATE()
  endif()
-- 
2.7.4