CMakeLists: Require CMake version 3.1 or newer

Although CMake version 3.0.2 was previously required, the policies
CMP0053 and CMP0054, introduced only in CMake version 3.1 and used
in this CMakeLists file, can have surprising effects under an older
CMake version.

Simplify the CMakeLists file by setting the global policy version
to 3.1, and remove the specific policy settings.

As an added bonus, remove the vestigial workarounds for all ancient
CMake versions.

CMakeLists.txt

@@ -17,25 +17,8 @@
 # For conditions of distribution and use, see the disclaimer
 # and license in png.h
 
-cmake_minimum_required(VERSION 3.0.2)
+cmake_minimum_required(VERSION 3.1)
-cmake_policy(VERSION 3.0.2)
+cmake_policy(VERSION 3.1)
-
-# Set MacOSX @rpath usage globally.
-if(POLICY CMP0020)
-  cmake_policy(SET CMP0020 NEW)
-endif()
-if(POLICY CMP0042)
-  cmake_policy(SET CMP0042 NEW)
-endif()
-# Use new variable expansion policy.
-if(POLICY CMP0053)
-  cmake_policy(SET CMP0053 NEW)
-endif()
-if(POLICY CMP0054)
-  cmake_policy(SET CMP0054 NEW)
-endif()
-
-set(CMAKE_CONFIGURATION_TYPES "Release;Debug;MinSizeRel;RelWithDebInfo")
 
 project(libpng C ASM)
 enable_testing()
@@ -636,19 +619,11 @@ function(png_add_test)
 
   configure_file("${CMAKE_CURRENT_SOURCE_DIR}/scripts/test.cmake.in"
                  "${CMAKE_CURRENT_BINARY_DIR}/tests/${_PAT_NAME}.cmake" @ONLY)
-  if(CMAKE_MAJOR_VERSION GREATER 2) # have generator expressions
+  add_test(NAME "${_PAT_NAME}"
-    add_test(NAME "${_PAT_NAME}"
+           COMMAND "${CMAKE_COMMAND}"
-             COMMAND "${CMAKE_COMMAND}"
+           "-DLIBPNG=$<TARGET_FILE:png>"
-             "-DLIBPNG=$<TARGET_FILE:png>"
+           "-DTEST_COMMAND=$<TARGET_FILE:${_PAT_COMMAND}>"
-             "-DTEST_COMMAND=$<TARGET_FILE:${_PAT_COMMAND}>"
+           -P "${CMAKE_CURRENT_BINARY_DIR}/tests/${_PAT_NAME}.cmake")
-             -P "${CMAKE_CURRENT_BINARY_DIR}/tests/${_PAT_NAME}.cmake")
-  else() # old 2.x add_test; limited and won't work well on Windows
-    # Note LIBPNG is a dummy value as there are no generator expressions
-    add_test("${_PAT_NAME}" "${CMAKE_COMMAND}"
-             "-DLIBPNG=${CMAKE_CURRENT_BINARY_DIR}/libpng.so"
-             "-DTEST_COMMAND=./${_PAT_COMMAND}"
-             -P "${CMAKE_CURRENT_BINARY_DIR}/tests/${_PAT_NAME}.cmake")
-  endif()
 endfunction()
 
 if(PNG_TESTS AND PNG_SHARED)
@@ -868,41 +843,35 @@ if(PNG_SHARED)
     CLEAN_DIRECT_OUTPUT 1)
 endif()
 
-# If CMake > 2.4.x, we set a variable used below to export
-# targets to an export file.
-# TODO: Use VERSION_GREATER after our cmake_minimum_required >= 2.6.2
-if(CMAKE_MAJOR_VERSION GREATER 1 AND CMAKE_MINOR_VERSION GREATER 4)
-  set(PNG_EXPORT_RULE EXPORT libpng)
-elseif(CMAKE_MAJOR_VERSION GREATER 2) # future proof
-  set(PNG_EXPORT_RULE EXPORT libpng)
-endif()
-
 # INSTALL
 if(NOT SKIP_INSTALL_LIBRARIES AND NOT SKIP_INSTALL_ALL)
   install(TARGETS ${PNG_LIB_TARGETS}
-      ${PNG_EXPORT_RULE}
+          EXPORT libpng
-      RUNTIME DESTINATION bin
+          RUNTIME DESTINATION bin
-      LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+          LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-      ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+          ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-      FRAMEWORK DESTINATION ${CMAKE_INSTALL_LIBDIR})
+          FRAMEWORK DESTINATION ${CMAKE_INSTALL_LIBDIR})
 
   if(PNG_SHARED)
     # Create a symlink for libpng.dll.a => libpng16.dll.a on Cygwin
     if(CYGWIN OR MINGW)
       create_symlink(libpng${CMAKE_IMPORT_LIBRARY_SUFFIX} TARGET png)
-      install(FILES $<TARGET_LINKER_FILE_DIR:png>/libpng${CMAKE_IMPORT_LIBRARY_SUFFIX} DESTINATION ${CMAKE_INSTALL_LIBDIR})
+      install(FILES $<TARGET_LINKER_FILE_DIR:png>/libpng${CMAKE_IMPORT_LIBRARY_SUFFIX}
+              DESTINATION ${CMAKE_INSTALL_LIBDIR})
     endif()
 
     if(NOT WIN32)
       create_symlink(libpng${CMAKE_SHARED_LIBRARY_SUFFIX} TARGET png)
-      install(FILES $<TARGET_LINKER_FILE_DIR:png>/libpng${CMAKE_SHARED_LIBRARY_SUFFIX} DESTINATION ${CMAKE_INSTALL_LIBDIR})
+      install(FILES $<TARGET_LINKER_FILE_DIR:png>/libpng${CMAKE_SHARED_LIBRARY_SUFFIX}
+              DESTINATION ${CMAKE_INSTALL_LIBDIR})
     endif()
   endif()
 
   if(PNG_STATIC)
     if(NOT WIN32 OR CYGWIN OR MINGW)
       create_symlink(libpng${CMAKE_STATIC_LIBRARY_SUFFIX} TARGET png_static)
-      install(FILES $<TARGET_LINKER_FILE_DIR:png_static>/libpng${CMAKE_STATIC_LIBRARY_SUFFIX} DESTINATION ${CMAKE_INSTALL_LIBDIR})
+      install(FILES $<TARGET_LINKER_FILE_DIR:png_static>/libpng${CMAKE_STATIC_LIBRARY_SUFFIX}
+              DESTINATION ${CMAKE_INSTALL_LIBDIR})
     endif()
   endif()
 endif()
@@ -920,7 +889,7 @@ endif()
 
 if(NOT SKIP_INSTALL_PROGRAMS AND NOT SKIP_INSTALL_ALL)
   install(TARGETS ${PNG_BIN_TARGETS}
-      RUNTIME DESTINATION bin)
+          RUNTIME DESTINATION bin)
 endif()
 
 if(NOT SKIP_INSTALL_FILES AND NOT SKIP_INSTALL_ALL)
@@ -943,9 +912,8 @@ if(NOT SKIP_INSTALL_FILES AND NOT SKIP_INSTALL_ALL)
   endif()
 endif()
 
-# On versions of CMake that support it, create an export file CMake
+# Create an export file that CMake users can include() to import our targets.
-# users can include() to import our targets
+if(NOT SKIP_INSTALL_EXPORT AND NOT SKIP_INSTALL_ALL)
-if(PNG_EXPORT_RULE AND NOT SKIP_INSTALL_EXPORT AND NOT SKIP_INSTALL_ALL)
   install(EXPORT libpng DESTINATION lib/libpng FILE lib${PNG_LIB_NAME}.cmake)
 endif()