Add CMake compatibility functions and macros

CMake/compatibility.cmake: define functions and macros to be used
  if a particular CMake functionality requires a higher CMake version
  than FLTK's minimum CMake version, see 'cmake_minimum_required(...)'
  in the root CMakeLists.txt.

Note: target_link_directories() is available since CMake 3.13

1 files changed, 74 insertions, 0 deletions

diff --git a/CMake/compatibility.cmake b/CMake/compatibility.cmake
new file mode 100644
index 000000000..338e9b9e3
--- /dev/null
+++ b/CMake/compatibility.cmake
@@ -0,0 +1,74 @@
+#
+# CMake compatibility functions and macros for the Fast Light Tool Kit (FLTK)
+#
+# Copyright 1998-2021 by Bill Spitzak and others.
+#
+# This library is free software. Distribution and use rights are outlined in
+# the file "COPYING" which should have been included with this file.  If this
+# file is missing or damaged, see the license at:
+#
+#     https://www.fltk.org/COPYING.php
+#
+# Please see the following page on how to report bugs and issues:
+#
+#     https://www.fltk.org/bugs.php
+#
+
+################################################################################
+#
+# The functions (and macros) in this file are defined to simplify CMake
+# code that uses features not available in all supported CMake versions.
+# Functions should be preferred (rather than macros) because functions
+# have their own variable scope.
+#
+# The function must apply a workaround for older versions or not add code
+# at all if there is no suitable workaround.
+#
+# The functions included here may be removed (with according changes of the
+# calling code) or the workaround code may be removed from the implementation
+# after cmake_minimum_required() has been raised to a version number greater
+# than or equal to the required version.
+#
+# Current cmake_minimum_required() version: see <fltk-root>/CMakeLists.txt
+#
+################################################################################
+
+################################################################################
+#
+# function fl_target_link_directories - add link directories to target
+#
+# Requires CMake version: 3.13
+# https://cmake.org/cmake/help/latest/command/target_link_directories.html
+#
+# Input:
+#
+# - TARGET: target to add link directories to, e.g. fluid
+#
+# - SCOPE: one of <INTERFACE|PUBLIC|PRIVATE> (see CMake docs)
+#
+# - DIRS: quoted list of link directories (separated by ';')
+#
+# The 'DIRS' argument takes a standard CMake list of directories, i.e. the
+# individual members must be separated by ';'. The list may be empty ("").
+# If more than one directory is to be added or if the list of directories
+# can be empty it *must* be quoted. This function may be called more than
+# once. Each invocation adds zero, one, or more directories.
+#
+# Example:
+#
+#   fl_target_link_directories (fluid PRIVATE "${PKG_CAIRO_LIBRARY_DIRS}")
+#
+#   In this example 'PKG_CAIRO_LIBRARY_DIRS' is platform dependent and
+#   can be an empty list.
+#
+################################################################################
+
+function (fl_target_link_directories TARGET SCOPE DIRS)
+
+  if (CMAKE_VERSION VERSION_LESS "3.13")
+    link_directories (${DIRS})
+  else ()
+    target_link_directories (${TARGET} ${SCOPE} ${DIRS})
+  endif ()
+
+endfunction () # fl_target_link_directories()