Some CMake handling improvements (#538)

* Some CMake handling improvements

- Set version from version.txt file if git retrieval fails
- Add FORCE flag to ETL_VERSION CACHE entry setting. The user
  should not have any reason to set this entry from the command line

* correction for cache entry text

* a little bit more context information

* message prefix for info printout

Co-authored-by: Robin Mueller <Robin Mueller>

CMakeLists.txt

@@ -5,7 +5,11 @@ cmake_minimum_required(VERSION 3.5.0)
 
 include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/helpers.cmake)
 
+set(MSG_PREFIX "etl |")
 determine_version_with_git(${GIT_DIR_LOOKUP_POLICY})
+if(NOT ETL_VERSION)
+    determine_version("version.txt")
+endif()
 
 project(etl VERSION ${ETL_VERSION})
 

cmake/helpers.cmake

@@ -3,9 +3,9 @@ function(determine_version VER_FILE_NAME)
     # Remove trailing whitespaces and/or newline
     string(STRIP ${ETL_VERSION_RAW} ETL_VERSION)
     set(ETL_VERSION ${ETL_VERSION} CACHE STRING
-        "ETL version determined from version.txt"
+        "ETL version determined from version.txt" FORCE
     )
-    message(STATUS "Determined ETL version ${ETL_VERSION} from version.txt file")
+    message(STATUS "${MSG_PREFIX} Determined ETL version ${ETL_VERSION} from version.txt file")
 endfunction()
 
 function(determine_version_with_git)
@@ -16,7 +16,7 @@ function(determine_version_with_git)
         message(WARNING "Version string ${VERSION} retrieved with git describe is invalid")
         return()
     endif()
-    message(STATUS ${VERSION})
+    message(STATUS "${MSG_PREFIX} Version string determined with git describe: ${VERSION}")
     # Parse the version information into pieces.
     string(REGEX REPLACE "^([0-9]+)\\..*" "\\1" VERSION_MAJOR "${VERSION}")
     string(REGEX REPLACE "^[0-9]+\\.([0-9]+).*" "\\1" VERSION_MINOR "${VERSION}")
@@ -25,7 +25,7 @@ function(determine_version_with_git)
     set(ETL_VERSION "${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH}")
 
     set(ETL_VERSION ${ETL_VERSION} CACHE STRING
-        "ETL version determined from version.txt"
+        "ETL version determined with git describe" FORCE
     )
-    message(STATUS "Determined ETL version ${ETL_VERSION} from the git tag")
+    message(STATUS "${MSG_PREFIX} Determined ETL version ${ETL_VERSION} from the git tag")
 endfunction()