cmake: Make build reproducible across different build directories

EchterAgo · EchterAgo · commit 1bda584b7bf7 · 2024-02-19T20:05:05.000+07:00
Without this, the usage of the __FILE__ macro leaves the build directory
in the binary. When building the Python extension with build isolation
enabled this would lead to random paths in the binary.
diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
@@ -44,6 +44,17 @@ else()
         -Wall -Wextra -Wno-missing-braces -Werror=undef -Werror=return-type)
 endif()
 
+include (CheckCXXCompilerFlag)
+
+# This is needed for reproducible builds across different build directories.
+# Without this, the usage of the __FILE__ macro leaves the build directory in
+# the binary. When building the Python extension with build isolation enabled
+# this would lead to random paths in the binary.
+set(FILE_PREFIX_ARG "-ffile-prefix-map=${CMAKE_CURRENT_SOURCE_DIR}=")
+check_cxx_compiler_flag("${FILE_PREFIX_ARG}" HAS_FILE_PREFIX_ARG)
+if(HAS_FILE_PREFIX_ARG)
+    set(ZXING_CORE_LOCAL_DEFINES ${ZXING_CORE_LOCAL_DEFINES} "${FILE_PREFIX_ARG}")
+endif()
 
 ################# Source files
 
@@ -458,8 +469,6 @@ target_compile_options (ZXing
     PRIVATE ${ZXING_CORE_LOCAL_DEFINES}
 )
 
-include (CheckCXXCompilerFlag)
-
 target_compile_features(ZXing PUBLIC cxx_std_17)
 
 target_link_libraries (ZXing PRIVATE Threads::Threads)
diff --git a/wrappers/python/CMakeLists.txt b/wrappers/python/CMakeLists.txt
@@ -17,8 +17,16 @@ if (NOT hasParent)
     option (BUILD_WRITERS "Build with writer support (encoders)" ON)
     option (BUILD_READERS "Build with reader support (decoders)" ON)
     set(BUILD_DEPENDENCIES "AUTO")
-    if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/core)
-        add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/core ZXing EXCLUDE_FROM_ALL)
+
+    set(CORE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/core)
+    if(IS_SYMLINK ${CORE_PATH})
+        # This is needed because otherwise GCC resolves the symlink which causes paths to randomly
+        # be prefixed by /core or by /wrappers/python/core depending on include order.
+        set(CORE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/../../core)
+    endif()
+
+    if(EXISTS ${CORE_PATH})
+        add_subdirectory(${CORE_PATH} ZXing EXCLUDE_FROM_ALL)
         include(${CMAKE_CURRENT_SOURCE_DIR}/zxing.cmake)
     else()
         message(FATAL_ERROR "Unable to locate zxing source code")
