cmake: Enable policy CMP0074 for ZLIB_ROOT; deprecate PNG_BUILD_ZLIB
Although the minimum required CMake version is 3.6, this policy will
only have effect under CMake 3.12 or newer.
Reported-by: Jacob Harding <54728054+jacobharding@users.noreply.github.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b592132..8c69756 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -48,6 +48,11 @@
VERSION ${PNGLIB_VERSION}
LANGUAGES C ASM)
+if(POLICY CMP0074)
+ # Allow find_package() to use the ZLIB_ROOT variable, if available.
+ cmake_policy(SET CMP0074 NEW)
+endif()
+
include(CheckCSourceCompiles)
include(GNUInstallDirs)
@@ -94,11 +99,23 @@
option(PNG_DEBUG "Enable debug output" OFF)
option(PNG_HARDWARE_OPTIMIZATIONS "Enable hardware optimizations" ON)
-# Allow the users to specify a location of zlib.
-# Useful if zlib is being built alongside this as a sub-project.
+# Allow the users to specify a custom location of zlib.
+# This option is deprecated, and no longer needed with CMake 3.12 and newer.
+# Under the CMake policy CMP0074, if zlib is being built alongside libpng as a
+# subproject, its location can be passed on to CMake via the ZLIB_ROOT variable.
option(PNG_BUILD_ZLIB "Custom zlib location, else find_package is used" OFF)
if(NOT PNG_BUILD_ZLIB)
find_package(ZLIB REQUIRED)
+elseif(POLICY CMP0074)
+ # TODO: Remove the policy check if CMake version 3.12 or greater becomes the minimum required.
+ if("x${ZLIB_ROOT}" STREQUAL "x")
+ message(DEPRECATION
+ "The option PNG_BUILD_ZLIB has been deprecated; please use ZLIB_ROOT instead")
+ else()
+ message(SEND_ERROR
+ "The option PNG_BUILD_ZLIB=${PNG_BUILD_ZLIB} and "
+ "the variable ZLIB_ROOT=\"${ZLIB_ROOT}\" are mutually exclusive")
+ endif()
endif()
if(UNIX AND NOT APPLE AND NOT BEOS AND NOT HAIKU AND NOT EMSCRIPTEN)
