One of Cygwin's goals is to build projects using the POSIX API with no
Windows awareness. Many CMake-built projects have been written to test
for UNIX and WIN32 but not CYGWIN. The preferred behavior under Cygwin
in such projects is to take the UNIX path but not the WIN32 path.
Unfortunately this change is BACKWARDS INCOMPATIBLE for Cygwin-aware
CMake projects! Some projects that previously built under Cygwin and
are Cygwin-aware when they test for WIN32 may now behave differently.
Eventually these projects will need to be updated, but to help users
build them in the meantime we print a warning about the change in
behavior. Furthermore, one may set CMAKE_LEGACY_CYGWIN_WIN32 to request
old behavior during the transition.
Normally we avoid backwards incompatible changes, but we make an
exception in this case for a few reasons:
(1) This behavior is preferred by Cygwin's design goals.
(2) A warning provides a clear path forward for everyone who may see
incompatible behavior, and CMAKE_LEGACY_CYGWIN_WIN32 provides a
compatibility option. The warning and compatibility option both
disappear when the minimum required version of CMake in a project is
sufficiently new, so this issue will simply go away over time as
projects are updated to account for the change.
(3) The fixes required to update projects are fairly insignificant.
Furthermore, the Cygwin distribution has no releases itself so project
versions that predate said fixes tend to be difficult to build anyway.
(4) This change enables many CMake-built projects that did not
previously build under Cygwin to work out-of-the-box. From bug #10122:
"I have built over 120 different source packages with (my patched)
CMake, including most of KDE4, and have found that NOT defining
WIN32 on Cygwin is much more accurate." -- Yaakov Selkowitz
A fully compatible change would require patches on top of these project
releases for Cygwin even though they otherwise need not be aware of it.
(5) Yaakov has been maintaining a fork of CMake with this change for the
Cygwin Ports distribution. It works well in practice. By accepting the
change in upstream CMake we avoid confusion between the versions.
CMake itself builds without WIN32 defined on Cygwin. Simply disable
CMAKE_LEGACY_CYGWIN_WIN32 explicitly in our own CMakeLists.txt file.
While Cygwin supports linking directly to .dll files, the behavior is
now discouraged. All Cygwin packages now provide import libraries of
the form lib*.dll.a and CMake has built the import libraries for years.
We believe it is now safe to stop explicitly searching for .dll files
because their import libraries will always be available when the
corresponding header files are available. Users can always set
find_library cache entries to point at a .dll file by hand if they
really must use one.
Change based on patch from issue #10122.
This moves GNU compiler flags into new-style modules
Compiler/GNU-<lang>.cmake
Platform/<os>-GNU-<lang>.cmake
We use language-independent helper modules
Compiler/GNU.cmake
Platform/<os>-GNU.cmake
to define macros consolidating the information.
This enables the --enable-auto-import linker flag on Cygwin when linking
executables. It works with the old gcc 3.x compiler and is necessary
for the new gcc 4.x compiler. See issue #9071.
cmMakefile.cxx, but now in the platform files and are now valid for the
target platform, not the host platform.
New variables CMAKE_HOST_WIN32, CMAKE_HOST_UNIX, CMAKE_HOST_APPLE and
CMAKE_HOST_CYGWIN have been added in cmMakefile.cxx (...and have now to be
used in all cmake files which are executed before
CMakeSystemSpecificInformation.cmake is loaded). For compatibility the old
set is set to the new one in CMakeDetermineSystem.cmake and reset before the
system platform files are loaded, so custom language or compiler modules
which use these should still work.
Alex
Kitware Robot
Brad King
Yaakov Selkowitz
Alexander Neundorf
Bill Hoffman