Use relative paths and provide message about base location

 - Otherwise, the install receipt will depend on install location, reducing the
   reproducibility of the build!

Author: zbeekman

cmake/InstallFileManifest.cmake

@@ -1,7 +1,10 @@
 # This script will create and install an install manifest, including SHA256 hashes of each installed file
 # Variables passed from CMake must be set with `install(CODE "set(...)")`
 
-message(STATUS "Generating SHA256 checksums for all installed assets")
+message(STATUS "Generating SHA256 checksumed receipt for all installed assets")
+
+# Set receipt install destination
+set(RECEIPT_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_DATADIR}/${PROJECT_NAME}")
 
 # Mimic cmake_install.cmake's handlin of components
 if(CMAKE_INSTALL_COMPONENT)
@@ -16,14 +19,18 @@ file(REMOVE "${CMAKE_BINARY_DIR}/${HASHED_INSTALL_MANIFEST}")
 # Loop over files computing hashes
 foreach(file IN LISTS CMAKE_INSTALL_MANIFEST_FILES)
   file(SHA256 "${file}" _file_sha256)
-  file(APPEND "${CMAKE_BINARY_DIR}/${HASHED_INSTALL_MANIFEST}" "${_file_sha256}  ${file}\n")
+  file(RELATIVE_PATH FILE_REL_PATH "${RECEIPT_INSTALL_DIR}" "${file}")
+  file(APPEND "${CMAKE_BINARY_DIR}/${HASHED_INSTALL_MANIFEST}" "${_file_sha256}  ${FILE_REL_PATH}\n")
 endforeach()
+file(APPEND "${CMAKE_BINARY_DIR}/${HASHED_INSTALL_MANIFEST}"
+  "# Paths relative to \${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_DATADIR}/${PROJECT_NAME}\n")
 
-file(INSTALL DESTINATION "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_DATADIR}/${PROJECT_NAME}" TYPE FILE PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ FILES
+file(INSTALL DESTINATION "${RECEIPT_INSTALL_DIR}" TYPE FILE PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ FILES
   "${CMAKE_BINARY_DIR}/${HASHED_INSTALL_MANIFEST}")
 
 file(SHA256 "${CMAKE_BINARY_DIR}/${HASHED_INSTALL_MANIFEST}" MANIFEST_SHA256)
 message(STATUS
-  "Global checksum for OpenCoarrays installation:\n${MANIFEST_SHA256}  ${HASHED_INSTALL_MANIFEST}")
+  "Global checksum for OpenCoarrays installation:
+       ${MANIFEST_SHA256}  ${HASHED_INSTALL_MANIFEST}")
 message(STATUS "${PROJECT_NAME} was configured with SOURCE_DATE_EPOCH=${SOURCE_DATE_EPOCH}")
 message(STATUS "The current environment has SOURCE_DATE_EPOCH set to: $ENV{SOURCE_DATE_EPOCH}")