[cmake-developers] Probable bug in message output from Modules/Platform/CYGWIN.cmake

[Alan W. Irwin]

On 2015-04-28 14:54-0700 Alan W. Irwin wrote:

> Also, a spurious warning is probably not that big a deal, but if you
> think the incorrect order of project(...) before
> cmake_minimum_required(...) could lead to more serious issues now or
> in the future as Platform code gets more and more complex, then I
> suggest you implement some code for one of those commands that
> enforces that order, subject, of course, to a policy so that you do
> not introduce backwards incompatibilities with this change.

Having thought about this some more, I am pretty sure what is going on
is if any language support file refers to
CMAKE_MINIMUM_REQUIRED_VERSION, then cmake_minimum_required must be
called to define that variable before enabling languages (e.g., via
project statements).

The rest of this post assumes the above explanation is the correct one.

To follow up, I looked at the files (some of which have to do with
language support) in the Modules tree for the master branch tip
version of CMake using the command

software at raven> find . -type f |xargs grep -l CMAKE_MINIMUM_REQUIRED_VERSION
./GenerateExportHeader.cmake
./Platform/CYGWIN.cmake
./CMakeExportBuildSettings.cmake
./FindPkgConfig.cmake
./CMakeDetermineVSServicePack.cmake
./WriteCompilerDetectionHeader.cmake
./Qt4Macros.cmake

If the only file in this list that affects language support is
Platform/CYGWIN.cmake, there was some alternative to using
CMAKE_MINIMUM_REQUIRED_VERSION in that logic, the C++ source code
implementing language support does not refer to
CMAKE_MINIMUM_REQUIRED_VERSION, and you can guarantee those conditions
for all future language support then that would permanently solve the
ordering issue as well. But, my feeling is the better practical
solution is some code (not used unless the relevant Policy is NEW) to
assure that cmake_minimum_required is always called (so that
CMAKE_MINIMUM_REQUIRED_VERSION is defined) before any language is
enabled.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
__________________________

Linux-powered Science
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