Windows: Optionally generate DLL module definition files automatically

Create target property WINDOWS_EXPORT_ALL_SYMBOLS to automatically
generate a module definition file from MS-compatible .obj files and give
it to the linker in order to export all symbols from the .dll part of a
SHARED library.

Help/manual/cmake-properties.7.rst

@@ -251,6 +251,7 @@ Properties on Targets
    /prop_tgt/VS_WINRT_EXTENSIONS
    /prop_tgt/VS_WINRT_REFERENCES
    /prop_tgt/WIN32_EXECUTABLE
+   /prop_tgt/WINDOWS_EXPORT_ALL_SYMBOLS
    /prop_tgt/XCODE_ATTRIBUTE_an-attribute
    /prop_tgt/XCTEST
 

Help/manual/cmake-variables.7.rst

@@ -275,6 +275,7 @@ Variables that Control the Build
    /variable/CMAKE_USE_RELATIVE_PATHS
    /variable/CMAKE_VISIBILITY_INLINES_HIDDEN
    /variable/CMAKE_VS_INCLUDE_INSTALL_TO_DEFAULT_BUILD
+   /variable/CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS
    /variable/CMAKE_WIN32_EXECUTABLE
    /variable/CMAKE_XCODE_ATTRIBUTE_an-attribute
    /variable/EXECUTABLE_OUTPUT_PATH

Help/prop_tgt/WINDOWS_EXPORT_ALL_SYMBOLS.rst

@@ -0,0 +1,18 @@
+WINDOWS_EXPORT_ALL_SYMBOLS
+--------------------------
+
+This property is implemented only for MS-compatible tools on Windows.
+
+Enable this boolean property to automatically create a module definition
+(``.def``) file with all global symbols found in the input ``.obj`` files
+for a ``SHARED`` library on Windows.  The module definition file will be
+passed to the linker causing all symbols to be exported from the ``.dll``.
+For global *data* symbols, ``__declspec(dllimport)`` must still be used when
+compiling against the code in the ``.dll``.  All other function symbols will
+be automatically exported and imported by callers.  This simplifies porting
+projects to Windows by reducing the need for explicit ``dllexport`` markup,
+even in ``C++`` classes.
+
+This property is initialized by the value of
+the :variable:`CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS` variable if it is set
+when a target is created.

Help/release/dev/auto_export_dll_symbols.rst

@@ -0,0 +1,6 @@
+auto_export_dll_symbols
+-----------------------
+
+* On Windows with MS-compatible tools, CMake learned to optionally
+  generate a module definition (``.def``) file for ``SHARED`` libraries.
+  See the :prop_tgt:`WINDOWS_EXPORT_ALL_SYMBOLS` target property.

Help/variable/CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS.rst

@@ -0,0 +1,6 @@
+CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS
+--------------------------------
+
+Default value for :prop_tgt:`WINDOWS_EXPORT_ALL_SYMBOLS` target property.
+This variable is used to initialize the property on each target as it is
+created.