cmake: Redo the fix for Clang support on Windows

Redo commit 70fda1837d5de802ce5f7e04be239192b6a74d92, with a redesign.

Define the variables PNG_SHARED_OUTPUT_NAME and PNG_STATIC_OUTPUT_NAME
for the benefit of the OUTPUT_NAME target properties of, respectively,
the shared libpng build and the static libpng build. Fix and improve
not only Clang, but also other Windows toolchains, such as Embarcadero.

Rename the variable PNGLIB_SHARED_SOVERSION to PNG_ABI_VERSION.
The applicability of this variable, which is much wider than the old
name used to suggest, includes the definitions of PNG_*_OUTPUT_NAME.

Delete the confusingly-named variables PNGLIB_NAME and PNG_LIB_NAME,
and rename PNG_LIB_TARGETS to PNG_LIBRARY_TARGETS.

Set the macros _CRT_SECURE_NO_DEPRECATE and _CRT_NONSTDC_NO_DEPRECATE,
for all compilers that use MSVC run-time library headers. Currently,
these compilers are MSVC and Clang/Windows.

Add or improve the comments that accompany user-serviceable variables
and options.

Co-authored-by: B. Scott Michel <scooter.phd@gmail.com>
Signed-off-by: Cosmin Truta <ctruta@gmail.com>

CMakeLists.txt

@@ -20,6 +20,7 @@
 # Revised by Owen Rudge, 2020
 # Revised by Gleb Mazovetskiy, 2021
 # Revised by Christopher Sean Morrison, 2022
+# Revised by B. Scott Michel, 2022
 # Revised by Jeremy Maitin-Shepard, 2022
 # Revised by Martin Storsjo, 2022
 # Revised by Jon Creighton, 2023
@@ -44,15 +45,31 @@ set(PNGLIB_MINOR 6)
 set(PNGLIB_REVISION 40)
 #set(PNGLIB_SUBREVISION 0)
 set(PNGLIB_SUBREVISION "git")
-set(PNGLIB_NAME libpng${PNGLIB_MAJOR}${PNGLIB_MINOR})
 set(PNGLIB_VERSION ${PNGLIB_MAJOR}.${PNGLIB_MINOR}.${PNGLIB_REVISION})
-set(PNGLIB_SHARED_SOVERSION ${PNGLIB_MAJOR}${PNGLIB_MINOR})
+set(PNGLIB_ABI_VERSION ${PNGLIB_MAJOR}${PNGLIB_MINOR})
-set(PNGLIB_SHARED_VERSION ${PNGLIB_SHARED_SOVERSION}.${PNGLIB_REVISION}.${PNGLIB_SUBREVISION})
+set(PNGLIB_SHARED_VERSION ${PNGLIB_ABI_VERSION}.${PNGLIB_REVISION}.${PNGLIB_SUBREVISION})
 
-# Allow users to specify location of zlib.
+# Allow the users to specify an application-specific API prefix for libpng
+# vendoring purposes. A standard libpng build should have no such prefix.
+set(PNG_PREFIX ""
+    CACHE STRING "Prefix to prepend to the API function names")
+
+# Allow the users to import their own extra configuration settings.
+set(DFA_XTRA ""
+    CACHE FILEPATH "File containing extra configuration settings")
+
+# Allow the users to configure the following build options.
+option(PNG_SHARED "Build libpng as a shared lib" ON)
+option(PNG_STATIC "Build libpng as a static lib" ON)
+option(PNG_FRAMEWORK "Build libpng as a Mac OS X framework" OFF)
+option(PNG_EXECUTABLES "Build libpng executables" ON)
+option(PNG_TESTS "Build libpng tests" ON)
+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.
-option(PNG_BUILD_ZLIB "Custom zlib Location, else find_package is used" OFF)
+option(PNG_BUILD_ZLIB "Custom zlib location, else find_package is used" OFF)
-
 if(NOT PNG_BUILD_ZLIB)
   find_package(ZLIB REQUIRED)
   include_directories(${ZLIB_INCLUDE_DIRS})
@@ -68,20 +85,6 @@ else()
   set(M_LIBRARY "")
 endif()
 
-# Public CMake configuration variables.
-option(PNG_SHARED "Build shared lib" ON)
-option(PNG_STATIC "Build static lib" ON)
-option(PNG_EXECUTABLES "Build libpng executables" ON)
-option(PNG_TESTS "Build libpng tests" ON)
-
-# Many more configuration options could be added here.
-option(PNG_FRAMEWORK "Build OS X framework" OFF)
-option(PNG_DEBUG "Build with debug output" OFF)
-option(PNG_HARDWARE_OPTIMIZATIONS "Enable hardware optimizations" ON)
-
-set(PNG_PREFIX "" CACHE STRING "Prefix to add to the API function names")
-set(DFA_XTRA "" CACHE FILEPATH "File containing extra configuration settings")
-
 # CMake currently sets CMAKE_SYSTEM_PROCESSOR to one of x86_64 or arm64 on macOS,
 # based upon the OS architecture, not the target architecture. As such, we need
 # to check CMAKE_OSX_ARCHITECTURES to identify which hardware-specific flags to
@@ -226,9 +229,6 @@ endif()
 
 endif(PNG_HARDWARE_OPTIMIZATIONS)
 
-# Set PNG_LIB_NAME.
-set(PNG_LIB_NAME png${PNGLIB_MAJOR}${PNGLIB_MINOR})
-
 # Distinguish between debug and release builds.
 set(CMAKE_DEBUG_POSTFIX "d")
 
@@ -600,7 +600,8 @@ set(png_fix_itxt_sources
     contrib/tools/png-fix-itxt.c
 )
 
-if(MSVC)
+if(MSVC OR (WIN32 AND (CMAKE_C_COMPILER_ID MATCHES ".*Clang")))
+  add_definitions(-D_CRT_NONSTDC_NO_DEPRECATE)
   add_definitions(-D_CRT_SECURE_NO_DEPRECATE)
 endif()
 
@@ -608,23 +609,38 @@ if(PNG_DEBUG)
   add_definitions(-DPNG_DEBUG)
 endif()
 
-# Now build our target.
+# Now build our targets.
 include_directories(${CMAKE_CURRENT_SOURCE_DIR} ${ZLIB_INCLUDE_DIRS})
 
-set(PNG_LIB_TARGETS "")
+# Initialize the list of libpng library targets.
+set(PNG_LIBRARY_TARGETS "")
+
+# Initialize the libpng library file names.
+if(UNIX
+   OR (WIN32 AND NOT "${CMAKE_SHARED_LIBRARY_PREFIX}" STREQUAL "")
+   OR (WIN32 AND NOT "${CMAKE_STATIC_LIBRARY_PREFIX}" STREQUAL ""))
+  # We are on a Unix or Unix-like toolchain like the GNU toolchain on Windows.
+  # Library file names are expected to have an implicit prefix such as "lib".
+  # Let CMake prepend and append its usual prefixes and suffixes by default.
+  set(PNG_SHARED_OUTPUT_NAME "png${PNGLIB_ABI_VERSION}")
+  set(PNG_STATIC_OUTPUT_NAME "png${PNGLIB_ABI_VERSION}")
+else()
+  # We are, most likely, on a Windows toolchain like MSVC, Clang on Windows,
+  # Borland/Embarcadero, etc. We need to specify the "libpng" name explicitly.
+  # We also need to use a custom suffix, in order to distinguish between the
+  # shared import library name and the static library name.
+  set(PNG_SHARED_OUTPUT_NAME "libpng${PNGLIB_ABI_VERSION}")
+  set(PNG_STATIC_OUTPUT_NAME "libpng${PNGLIB_ABI_VERSION}_static")
+endif()
 
 if(PNG_SHARED)
   add_library(png_shared SHARED ${libpng_sources})
   add_dependencies(png_shared png_genfiles)
-  list(APPEND PNG_LIB_TARGETS png_shared)
+  list(APPEND PNG_LIBRARY_TARGETS png_shared)
-  set_target_properties(png_shared PROPERTIES OUTPUT_NAME ${PNG_LIB_NAME})
+  set_target_properties(png_shared PROPERTIES
-  if(MSVC)
+                        OUTPUT_NAME "${PNG_SHARED_OUTPUT_NAME}"
-    # MSVC does not append 'lib'. Do it here, to have consistent names.
+                        VERSION "${PNGLIB_SHARED_VERSION}"
-    set_target_properties(png_shared PROPERTIES PREFIX "lib")
+                        SOVERSION "${PNGLIB_ABI_VERSION}")
-    set_target_properties(png_shared PROPERTIES IMPORT_PREFIX "lib")
-  endif()
-  target_link_libraries(png_shared ${ZLIB_LIBRARIES} ${M_LIBRARY})
-
   if(UNIX AND AWK)
     if(HAVE_LD_VERSION_SCRIPT)
       set_target_properties(png_shared PROPERTIES
@@ -637,46 +653,35 @@ if(PNG_SHARED)
   if(WIN32)
     set_target_properties(png_shared PROPERTIES DEFINE_SYMBOL PNG_BUILD_DLL)
   endif()
+  target_link_libraries(png_shared ${ZLIB_LIBRARIES} ${M_LIBRARY})
 endif()
 
 if(PNG_STATIC)
   add_library(png_static STATIC ${libpng_sources})
   add_dependencies(png_static png_genfiles)
-  list(APPEND PNG_LIB_TARGETS png_static)
+  list(APPEND PNG_LIBRARY_TARGETS png_static)
-  # MSVC doesn't use a different file extension for shared vs. static
-  # libs. We are able to change OUTPUT_NAME to remove the _static
-  # for all other platforms.
-  if(NOT MSVC)
   set_target_properties(png_static PROPERTIES
-                          OUTPUT_NAME "${PNG_LIB_NAME}")
+                        OUTPUT_NAME "${PNG_STATIC_OUTPUT_NAME}")
-  else()
-    set_target_properties(png_static PROPERTIES
-                          OUTPUT_NAME "${PNG_LIB_NAME}_static")
-  endif()
-  if(MSVC)
-    # MSVC does not append 'lib'. Do it here, to have consistent name.
-    set_target_properties(png_static PROPERTIES PREFIX "lib")
-  endif()
   target_link_libraries(png_static ${ZLIB_LIBRARIES} ${M_LIBRARY})
 endif()
 
 if(PNG_FRAMEWORK)
   add_library(png_framework SHARED ${libpng_sources})
   add_dependencies(png_framework png_genfiles)
-  list(APPEND PNG_LIB_TARGETS png_framework)
+  list(APPEND PNG_LIBRARY_TARGETS png_framework)
   set_target_properties(png_framework PROPERTIES
                         FRAMEWORK TRUE
-                        FRAMEWORK_VERSION ${PNGLIB_VERSION}
+                        FRAMEWORK_VERSION "${PNGLIB_VERSION}"
-                        MACOSX_FRAMEWORK_SHORT_VERSION_STRING ${PNGLIB_MAJOR}.${PNGLIB_MINOR}
+                        MACOSX_FRAMEWORK_SHORT_VERSION_STRING "${PNGLIB_MAJOR}.${PNGLIB_MINOR}"
-                        MACOSX_FRAMEWORK_BUNDLE_VERSION ${PNGLIB_VERSION}
+                        MACOSX_FRAMEWORK_BUNDLE_VERSION "${PNGLIB_VERSION}"
-                        MACOSX_FRAMEWORK_IDENTIFIER org.libpng.libpng
+                        MACOSX_FRAMEWORK_IDENTIFIER "org.libpng.libpng"
                         XCODE_ATTRIBUTE_INSTALL_PATH "@rpath"
                         PUBLIC_HEADER "${libpng_public_hdrs}"
-                        OUTPUT_NAME png)
+                        OUTPUT_NAME "png")
   target_link_libraries(png_framework ${ZLIB_LIBRARIES} ${M_LIBRARY})
 endif()
 
-if(NOT PNG_LIB_TARGETS)
+if(NOT PNG_LIBRARY_TARGETS)
   message(SEND_ERROR "No library variant selected to build. "
                      "Please enable at least one of the following options: "
                      "PNG_SHARED, PNG_STATIC, PNG_FRAMEWORK")
@@ -958,25 +963,18 @@ if(NOT WIN32 OR CYGWIN OR MINGW)
   set(includedir  ${CMAKE_INSTALL_FULL_INCLUDEDIR})
   set(LIBS        "-lz -lm")
   configure_file(${CMAKE_CURRENT_SOURCE_DIR}/libpng.pc.in
-                 ${CMAKE_CURRENT_BINARY_DIR}/${PNGLIB_NAME}.pc
+                 ${CMAKE_CURRENT_BINARY_DIR}/libpng${PNGLIB_ABI_VERSION}.pc
                  @ONLY)
-  create_symlink(libpng.pc FILE ${PNGLIB_NAME}.pc)
+  create_symlink(libpng.pc FILE libpng${PNGLIB_ABI_VERSION}.pc)
   configure_file(${CMAKE_CURRENT_SOURCE_DIR}/libpng-config.in
-                 ${CMAKE_CURRENT_BINARY_DIR}/${PNGLIB_NAME}-config
+                 ${CMAKE_CURRENT_BINARY_DIR}/libpng${PNGLIB_ABI_VERSION}-config
                  @ONLY)
-  create_symlink(libpng-config FILE ${PNGLIB_NAME}-config)
+  create_symlink(libpng-config FILE libpng${PNGLIB_ABI_VERSION}-config)
-endif()
-
-# Set up links.
-if(PNG_SHARED)
-  set_target_properties(png_shared PROPERTIES
-                        VERSION ${PNGLIB_SHARED_VERSION}
-                        SOVERSION ${PNGLIB_SHARED_SOVERSION})
 endif()
 
 # Install.
 if(NOT SKIP_INSTALL_LIBRARIES AND NOT SKIP_INSTALL_ALL)
-  install(TARGETS ${PNG_LIB_TARGETS}
+  install(TARGETS ${PNG_LIBRARY_TARGETS}
           EXPORT libpng
           RUNTIME DESTINATION bin
           LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
@@ -1011,13 +1009,13 @@ if(NOT SKIP_INSTALL_HEADERS AND NOT SKIP_INSTALL_ALL)
   install(FILES ${libpng_public_hdrs}
           DESTINATION include)
   install(FILES ${libpng_public_hdrs}
-          DESTINATION include/${PNGLIB_NAME})
+          DESTINATION include/libpng${PNGLIB_ABI_VERSION})
 endif()
 if(NOT SKIP_INSTALL_EXECUTABLES AND NOT SKIP_INSTALL_ALL)
   if(NOT WIN32 OR CYGWIN OR MINGW)
     install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/libpng-config
             DESTINATION bin)
-    install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/${PNGLIB_NAME}-config
+    install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/libpng${PNGLIB_ABI_VERSION}-config
             DESTINATION bin)
   endif()
 endif()
@@ -1039,9 +1037,9 @@ if(NOT SKIP_INSTALL_FILES AND NOT SKIP_INSTALL_ALL)
             DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)
     install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/libpng-config
             DESTINATION ${CMAKE_INSTALL_BINDIR})
-    install(FILES ${CMAKE_CURRENT_BINARY_DIR}/${PNGLIB_NAME}.pc
+    install(FILES ${CMAKE_CURRENT_BINARY_DIR}/libpng${PNGLIB_ABI_VERSION}.pc
             DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)
-    install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/${PNGLIB_NAME}-config
+    install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/libpng${PNGLIB_ABI_VERSION}-config
             DESTINATION ${CMAKE_INSTALL_BINDIR})
   endif()
 endif()
@@ -1050,7 +1048,7 @@ endif()
 if(NOT SKIP_INSTALL_EXPORT AND NOT SKIP_INSTALL_ALL)
   install(EXPORT libpng
           DESTINATION lib/libpng
-          FILE lib${PNG_LIB_NAME}.cmake)
+          FILE libpng${PNGLIB_ABI_VERSION}.cmake)
 endif()
 
 # TODO: Create MSVC import lib for MinGW-compiled shared lib.