[CMake] Passing CMAKE_TOOLCHAIN_FILE on command line causes CMake warning

[David Cole]

-----Original Message-----

From: Pat Marion <pat.marion at kitware.com>
To: David Cole <dlrdave at aol.com>
Cc: themiwi <themiwi at gmail.com>; cmake <cmake at cmake.org>
Sent: Wed, Feb 6, 2013 8:34 am
Subject: Re: [CMake] Passing CMAKE_TOOLCHAIN_FILE on command line causes CMake warning


I'd like you to try pasting the following text into a google search, so you can appreciate how widespread the warning is, 257 results from lots of different projects:


CMake Warning:   Manually-specified variables were not used by the project:      CMAKE_TOOLCHAIN_FILE


Most of these projects are not going to incorporate workarounds.  The warning is confusing to lots of users, and they're already unsure of the while crosscompiling thing, so seeing a warning adds uncertainty that they're doing it right.  Adding a workaround into the target project is not always possible since you might not have commit access or are compiling a previously released, stable version.

Pat




On Wed, Feb 6, 2013 at 10:51 PM, David Cole <dlrdave at aol.com> wrote:

If you don't want to see the warning, then also pass in --no-warn-unused-cli on the command line.

  --no-warn-unused-cli        = Don't warn about command line options.

 
But that suppresses the warning for all unreferenced variables.

Or... add:

  message(STATUS "CMAKE_TOOLCHAIN_FILE='${CMAKE_TOOLCHAIN_FILE}'")

 
to the project's CMakeLists.txt file so the variable is always referenced.

 
The point is: CMAKE_TOOLCHAIN_FILE is only read on the first configure. After that point, all toolchain stuff is cached and the file is unnecessary for subsequent configures.

That bug should just be closed as "won't fix" because it's not a bug. It's the intended behavior, and there are multiple ways to avoid the legitimate warning.


Just my opinion,
D





-----Original Message-----
From: Pat Marion <pat.marion at kitware.com>
To: Michael Wild <themiwi at gmail.com>
Cc: cmake <cmake at cmake.org>
Sent: Wed, Feb 6, 2013 7:23 am
Subject: Re: [CMake] Passing CMAKE_TOOLCHAIN_FILE on command line causes CMake warning


That's a pretty messy workaround though, I think.  ExternalProject_Add passes in lots of variables, including ones that do not typically change, like CMAKE_CXX_COMPILER.  Why impose a special requirement on the CMAKE_TOOLCHAIN_FILE variable?  Would a patch to avoid the warning be a welcome change, or is there a reason the warning should remain?

Pat


On Wed, Feb 6, 2013 at 9:52 PM, Michael Wild <themiwi at gmail.com> wrote:

Hi




On Wed, Feb 6, 2013 at 11:59 AM, Pat Marion <pat.marion at kitware.com> wrote:

Hi,

I'm emailing about bug 13093 in the backlog.  I found comments by Brad that suggest it's a legitimate warning, but I'm not sure how a project could avoid the warning.


By not specifying the toolchain file, for instance? If you have the problem in conjunction with ExternalProject_Add, check whether the CMakeCache.txt file exists in the build tree of the external project. If not, include the flag, otherwise drop it. 

My 2c

Michael





 

--

Powered by www.kitware.com

Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html

Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ

Follow this link to subscribe/unsubscribe:
http://www.cmake.org/mailman/listinfo/cmake

 



I appreciate the widespread nature of "the problem." Really, I do. (If you do the same search, but without CMAKE_TOOLCHAIN_FILE, you get 20,000+ results.)

The intent of the warning feature is to point out that you may have misspelled a variable name, since usually, variables specified on the command line *are* in fact, referenced during the configure or generate steps.

Unfortunately, the text of the warning does not say "you may have misspelled this, double-check your spelling". Nor does it say the more clear "this variable was not referenced at all by any of the CMakeLists code used during configuration or generation". It could even say "reference the variable, or use --no-warn-unused-cli to eliminate this warning" -- but it doesn't.

The other positive effect here is that it may point out that you're not using all the variables that you think you're using. Therefore, you may be able to simplify your command line, or your CMakeLists files.


I'm not a big fan of special-casing variable names for code like this. But if CMAKE_TOOLCHAIN_FILE is really "special", then maybe that's the right call here. You could certainly check if it's the same as the cached value, and only warn if it's different. If you do add such a warning, use text something like "start with a completely clean build tree if you are changing toolchain files" when a difference is detected.


Cheers,
D


 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.cmake.org/pipermail/cmake/attachments/20130206/5e0d1a51/attachment.htm>