CMake: for Windows builds, defaults PROJ DLL to be just 'proj_${PROJ_…

…MAJOR_VERSION}.dll'

instead of "proj_${PROJ_MAJOR_VERSION}_${PROJ_MINOR_VERSION}.dll"

This is configurable (for all platforms) by setting the new
PROJ_OUTPUT_NAME Make Variable

On MinGW, the APPEND_SOVERSION option can be set to ON, to add a "-${PROJ_SOVERSION}"
suffix to the PROJ shared library name.

Fixes #4151

cmake/ProjUtilities.cmake

@@ -34,34 +34,6 @@ function(print_variable NAME)
   message(STATUS "${NAME}${varpadding} = ${${NAME}}")
 endfunction()
 
-#
-# Generates output name for given target depending on platform and version.
-# For instance, on Windows, dynamic link libraries get ABI version suffix
-# proj_X_Y.dll.
-#
-
-function(proj_target_output_name TARGET_NAME OUTPUT_NAME)
-  if(NOT DEFINED TARGET_NAME)
-    message(SEND_ERROR "Error, the variable TARGET_NAME is not defined!")
-  endif()
-
-  if(NOT DEFINED ${PROJECT_NAME}_VERSION)
-    message(SEND_ERROR
-      "Error, the variable ${${PROJECT_NAME}_VERSION} is not defined!")
-  endif()
-
-  # On Windows, ABI version is specified using binary file name suffix.
-  # On Unix, suffix is empty and SOVERSION is used instead.
-  if(WIN32)
-    string(LENGTH "${${PROJECT_NAME}_ABI_VERSION}" abilen)
-    if(abilen GREATER 0)
-      set(SUFFIX "_${${PROJECT_NAME}_ABI_VERSION}")
-    endif()
-  endif()
-
-  set(${OUTPUT_NAME} ${TARGET_NAME}${SUFFIX} PARENT_SCOPE)
-endfunction()
-
 #
 # Configure a pkg-config file proj.pc
 # See also ProjInstallPath.cmake

cmake/ProjVersion.cmake

@@ -37,16 +37,5 @@ macro(proj_version)
 ${${PROJECT_NAME}_VERSION_MINOR}.\
 ${${PROJECT_NAME}_VERSION_PATCH}")
 
-  # Set ABI version string used to name binary output
-  # On Windows, ABI version is specified using binary file name suffix.
-  if(WIN32)
-    set(${PROJECT_NAME}_ABI_VERSION
-      "${${PROJECT_NAME}_VERSION_MAJOR}_\
-${${PROJECT_NAME}_VERSION_MINOR}")
-  endif()
-
   print_variable(${PROJECT_NAME}_VERSION)
-  if(WIN32)
-    print_variable(${PROJECT_NAME}_ABI_VERSION)
-  endif()
 endmacro()

docs/source/install.rst

@@ -287,6 +287,26 @@ All cached entries can be viewed using ``cmake -LAH`` from a build directory.
         or by specifying ``--config Release`` with CMake
         multi-configuration build tools (see example below).
 
+.. option:: PROJ_OUTPUT_NAME
+
+    .. versionadded:: 9.5
+
+    Sets the name of the PROJ library (excluding extension).
+    This generally defaults to "proj", except on Windows, where this defaults to
+    "proj_${PROJ_MAJOR_VERSION}" if APPEND_SOVERSION is OFF.
+
+    .. note::
+        For PROJ >= 6.0 and up to 9.4.1, on Windows, this was hardcoded to
+        "proj_${PROJ_MAJOR_VERSION}_${PROJ_MINOR_VERSION}".
+
+.. option:: APPEND_SOVERSION=OFF
+
+    .. versionadded:: 9.5
+
+    This variable can be set to ON for MinGW builds where BUILD_SHARED_LIBS=ON,
+    to add a "-${PROJ_SOVERSION}" suffix to the PROJ shared library name.
+    When this variable is set, PROJ_OUTPUT_NAME defaults to "proj"
+
 .. option:: CMAKE_C_COMPILER
 
     C compiler. Ignored for some generators, such as Visual Studio.

src/lib_proj.cmake

@@ -372,7 +372,6 @@ set(ALL_LIBPROJ_SOURCES
 set(ALL_LIBPROJ_HEADERS ${HEADERS_LIBPROJ})
 
 # Configuration for the core target "proj"
-proj_target_output_name(proj PROJ_CORE_TARGET_OUTPUT_NAME)
 
 add_library(proj
   ${ALL_LIBPROJ_SOURCES}
@@ -410,13 +409,37 @@ target_include_directories(proj INTERFACE
   $<BUILD_INTERFACE:${PROJ_SOURCE_DIR}/include>
   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 
+if(WIN32)
+    if (MINGW AND BUILD_SHARED_LIBS)
+        option(APPEND_SOVERSION "Whether to include shared object version as a suffix in the name of the PROJ shared library name." OFF)
+    endif()
+    if(MINGW AND BUILD_SHARED_LIBS AND APPEND_SOVERSION)
+        set(PROJ_OUTPUT_NAME "proj" CACHE STRING "Name of the PROJ library")
+    else()
+        # Detect major version update if re-using a CMake build directory where the
+        # PROJ version major number has been updated in the meantime.
+        math(EXPR PROJ_VERSION_MAJOR_MINUS_ONE "${PROJ_VERSION_MAJOR} - 1")
+        if(DEFINED PROJ_OUTPUT_NAME AND PROJ_OUTPUT_NAME STREQUAL "proj_${PROJ_VERSION_MAJOR_MINUS_ONE}")
+            message(WARNING "PROJ_OUTPUT_NAME was set to ${PROJ_OUTPUT_NAME}. Updating it to proj_${PROJ_VERSION_MAJOR}")
+            unset(PROJ_OUTPUT_NAME CACHE)
+        endif()
+        set(PROJ_OUTPUT_NAME "proj_${PROJ_VERSION_MAJOR}" CACHE STRING "Name of the PROJ library")
+    endif()
+else()
+    set(PROJ_OUTPUT_NAME "proj" CACHE STRING "Name of the PROJ library")
+endif()
+
+set_target_properties(proj PROPERTIES OUTPUT_NAME ${PROJ_OUTPUT_NAME})
+
 if(WIN32)
   set_target_properties(proj
     PROPERTIES
     VERSION "${PROJ_VERSION}"
-    OUTPUT_NAME "${PROJ_CORE_TARGET_OUTPUT_NAME}"
     ARCHIVE_OUTPUT_NAME proj
     CLEAN_DIRECT_OUTPUT 1)
+    if (MINGW AND BUILD_SHARED_LIBS AND APPEND_SOVERSION)
+        set_target_properties(proj PROPERTIES SUFFIX "-${PROJ_SOVERSION}${CMAKE_SHARED_LIBRARY_SUFFIX}")
+    endif()
 elseif(BUILD_FRAMEWORKS_AND_BUNDLE)
   set_target_properties(proj
     PROPERTIES