CMake: avoid referencing 'EXPAT_INCLUDE_DIRS' unless Expat has been sought

CMake when using `--warn-uninitialized -Werror=dev` notices that this variable
is being incorrectly referenced when `-Dwith_expat=OFF`:

  CMake Error (dev) at lib/common/CMakeLists.txt:111
    (target_include_directories):
    uninitialized variable 'EXPAT_INCLUDE_DIRS'

Gitlab: #2291

diff --git a/lib/common/CMakeLists.txt b/lib/common/CMakeLists.txt
index 3a167d483a916d47888d0b2afb0aac13bd799097..796ed42974058b58db06b2e9830ae3a3a508f04f 100644 (file)
--- a/lib/common/CMakeLists.txt
+++ b/lib/common/CMakeLists.txt
@@ -108,9 +108,11 @@ target_include_directories(common_obj PRIVATE
   ../xdot
 )
 
-target_include_directories(common_obj SYSTEM PRIVATE
-  ${EXPAT_INCLUDE_DIRS}
-)
+if(EXPAT_FOUND)
+  target_include_directories(common_obj SYSTEM PRIVATE
+    ${EXPAT_INCLUDE_DIRS}
+  )
+endif()
 
 if(WIN32)
   target_include_directories(common_obj