write_basic_package_version_file: add ExactVersion mode

This mode is for packages which consider themselves only compatible if
exactly the same version is requested. The tweak version is ignored.

Alex

Modules/BasicConfigVersion-ExactVersion.cmake.in

+# This is a basic version file for the Config-mode of find_package().
+# It is used by write_basic_package_version_file() as input file for configure_file()
+# to create a version-file which can be installed along a config.cmake file.
+#
+# The created file sets PACKAGE_VERSION_EXACT if the current version string and
+# the requested version string are exactly the same and it sets
+# PACKAGE_VERSION_COMPATIBLE if the current version is equal to the requested version.
+# The tweak version component is ignored.
+# The variable CVF_VERSION must be set before calling configure_file().
+
+
+set(PACKAGE_VERSION "@CVF_VERSION@")
+
+if("@CVF_VERSION@" MATCHES "^([0-9]+\\.[0-9]+\\.[0-9]+)\\..*") # strip the tweak version
+  set(CVF_VERSION_NO_TWEAK "${CMAKE_MATCH_1}")
+else()
+  set(CVF_VERSION_NO_TWEAK "@CVF_VERSION@")
+endif()
+
+if("${PACKAGE_FIND_VERSION}" MATCHES "^([0-9]+\\.[0-9]+\\.[0-9]+)\\..*") # strip the tweak version
+  set(REQUESTED_VERSION_NO_TWEAK "${CMAKE_MATCH_1}")
+else()
+  set(REQUESTED_VERSION_NO_TWEAK "${PACKAGE_FIND_VERSION}")
+endif()
+
+if("${REQUESTED_VERSION_NO_TWEAK}" STREQUAL "${CVF_VERSION_NO_TWEAK}")
+  set(PACKAGE_VERSION_COMPATIBLE TRUE)
+else()
+  set(PACKAGE_VERSION_COMPATIBLE FALSE)
+endif()
+
+if( "${PACKAGE_FIND_VERSION}" STREQUAL "${PACKAGE_VERSION}")
+  set(PACKAGE_VERSION_EXACT TRUE)
+endif()
+
+
+# check that the installed version has the same 32/64bit-ness as the one which is currently searching:
+if(NOT "${CMAKE_SIZEOF_VOID_P}" STREQUAL "@CMAKE_SIZEOF_VOID_P@")
+  math(EXPR installedBits "@CMAKE_SIZEOF_VOID_P@ * 8")
+  set(PACKAGE_VERSION "${PACKAGE_VERSION} (${installedBits}bit)")
+  set(PACKAGE_VERSION_UNSUITABLE TRUE)
+endif()

Modules/CMakePackageConfigHelpers.cmake

@@ -61,7 +61,7 @@
 # For an example see below the documentation for WRITE_BASIC_PACKAGE_VERSION_FILE().
 #
 #
-#  WRITE_BASIC_PACKAGE_VERSION_FILE( filename VERSION major.minor.patch COMPATIBILITY (AnyNewerVersion|SameMajorVersion) )
+#  WRITE_BASIC_PACKAGE_VERSION_FILE( filename VERSION major.minor.patch COMPATIBILITY (AnyNewerVersion|SameMajorVersion|ExactVersion) )
 #
 # Writes a file for use as <package>ConfigVersion.cmake file to <filename>.
 # See the documentation of FIND_PACKAGE() for details on this.
@@ -76,6 +76,10 @@
 # not be considered compatible if 1.0 is requested.
 # This mode should be used for packages which guarantee backward compatibility within the
 # same major version.
+# If ExactVersion is used, then the package is only considered compatible if the requested
+# version matches exactly its own version number (not considering the tweak version).
+# For example, version 1.2.3 of a package is only considered compatible to requested version 1.2.3.
+# This mode is for packages without compatibility guarantees.
 # If your project has more elaborated version matching rules, you will need to write your
 # own custom ConfigVersion.cmake file instead of using this macro.
 #