Define Git and date constants in executables only (#4681)

src/CMakeLists.txt

@@ -1,4 +1,5 @@
 set(LIBRARY_PROJECT "${PROJECT_NAME}-lib")
+set(VERSION_PROJECT "${LIBRARY_PROJECT}-version")
 set(EXECUTABLE_PROJECT "${PROJECT_NAME}")
 add_compile_definitions(QT_DISABLE_DEPRECATED_BEFORE=0x050F00)
 
@@ -46,8 +47,6 @@ set(SOURCE_FILES
         common/NetworkResult.hpp
         common/QLogging.cpp
         common/QLogging.hpp
-        common/Version.cpp
-        common/Version.hpp
         common/WindowDescriptors.cpp
         common/WindowDescriptors.hpp
 
@@ -799,15 +798,26 @@ set_target_properties(${LIBRARY_PROJECT}
     AUTOUIC ON
     )
 
-# Used to provide a date of build in the About page (for nightly builds). Getting the actual time of
-# compilation in CMake is a more involved, as documented in https://stackoverflow.com/q/24292898.
-# For CI runs, however, the date of build file generation should be consistent with the date of
-# compilation so this approximation is "good enough" for our purpose.
-if (DEFINED ENV{CHATTERINO_SKIP_DATE_GEN})
-    set(cmake_gen_date "1970-01-01")
-else ()
-    string(TIMESTAMP cmake_gen_date "%Y-%m-%d")
-endif ()
+# The version project has definitions about the build.
+# To avoid recompilations because of changing preprocessor definitions,
+# this is its own project.
+set(VERSION_SOURCE_FILES common/Version.cpp common/Version.hpp)
+add_library(${VERSION_PROJECT} STATIC ${VERSION_SOURCE_FILES})
+
+# source group for IDEs
+source_group(TREE ${CMAKE_SOURCE_DIR} FILES ${VERSION_SOURCE_FILES})
+target_include_directories(${VERSION_PROJECT} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+target_link_libraries(${VERSION_PROJECT} PRIVATE Qt${MAJOR_QT_VERSION}::Core)
+target_compile_definitions(${VERSION_PROJECT} PRIVATE
+    CHATTERINO_GIT_HASH=\"${GIT_HASH}\"
+    CHATTERINO_GIT_RELEASE=\"${GIT_RELEASE}\"
+    CHATTERINO_GIT_COMMIT=\"${GIT_COMMIT}\"
+    CHATTERINO_GIT_MODIFIED=${GIT_MODIFIED}
+
+    CHATTERINO_CMAKE_GEN_DATE=\"${cmake_gen_date}\"
+)
+
+target_link_libraries(${LIBRARY_PROJECT} PRIVATE ${VERSION_PROJECT})
 
 target_compile_definitions(${LIBRARY_PROJECT} PUBLIC
     CHATTERINO
@@ -815,18 +825,7 @@ target_compile_definitions(${LIBRARY_PROJECT} PUBLIC
     AB_CUSTOM_SETTINGS
     IRC_STATIC
     IRC_NAMESPACE=Communi
-
-    CHATTERINO_GIT_HASH=\"${GIT_HASH}\"
-    CHATTERINO_GIT_RELEASE=\"${GIT_RELEASE}\"
-    CHATTERINO_GIT_COMMIT=\"${GIT_COMMIT}\"
-
-    CHATTERINO_CMAKE_GEN_DATE=\"${cmake_gen_date}\"
     )
-if (GIT_MODIFIED)
-    target_compile_definitions(${LIBRARY_PROJECT} PUBLIC
-        CHATTERINO_GIT_MODIFIED
-        )
-endif ()
 if (USE_SYSTEM_QTKEYCHAIN)
     target_compile_definitions(${LIBRARY_PROJECT} PUBLIC
         CMAKE_BUILD