[cmake-developers] find_package error wording

[Alexander Neundorf]

On Friday 17 February 2012, Alexander Neundorf wrote:
> On Friday 17 February 2012, Brad King wrote:
...
> > Perhaps we can make the distinction between user and developer right
> > in the message.  When there is no Find module the proper message that
> > a user sees should talk about ecm_DIR and CMAKE_PREFIX_PATH only.
> > This should be the focus.  We can then add an extra note to help
> > 
> > developers use Find modules.  Consider:
> >   CMake Error at CMakeLists.txt:7 (find_package):
> >     No package configuration file for "ecm" found by names:
> >       ecmConfig.cmake
> >       ecm-config.cmake
> >     
> >     Add the installation prefix of "ecm" to CMAKE_PREFIX_PATH or
> >     set "ecm_DIR" to a directory containing one of the above files.
> >     
> >     (If you are a developer expecting this find_package to load a
> >     
> >      Findecm.cmake module then ensure it lies in CMAKE_MODULE_PATH.)
> 
> I'm still not convinced.
> Just today I found this commit from last October in kdelibs:
> http://quickgit.kde.org/index.php?p=kdelibs.git&a=commitdiff&h=ca501aa9f4c1
> e7adcd42accbd53538502ba50ce3&hp=3186e7a5f3acfaa5b5ac1b5cce9315eb53f54655
> 
> Commit message: on win32 we need access to the installed cmake modules dir
> 
> --- a/cmake/modules/FindKDE4Internal.cmake
> +++ b/cmake/modules/FindKDE4Internal.cmake
> @@ -736,6 +736,7 @@ endif(${CMAKE_MAJOR_VERSION}.${CMAKE_MIN
>  option(KDE4_ENABLE_FPIE  "Enable platform supports PIE linking")
> 
>   if (WIN32)
> +   list(APPEND CMAKE_MODULE_PATH
>                "${CMAKE_INSTALL_PREFIX}/share/apps/cmake/modules")
>     find_package(KDEWin REQUIRED)
>     option(KDE4_ENABLE_UAC_MANIFEST "add manifest to make..." OFF)
>     if (KDE4_ENABLE_UAC_MANIFEST)
> 
> 
> This looks really wrong (I mean this directory is not guaranteed to exist
> at all at cmake time, so it can't help finding a module file), and it was
> committed by a developer who is using cmake now already since 2006 at
> least.
> 
> If I would build this, I would get exactly to case 1) - neither Find-module
> nor config-file found.
> As user I should assume that there should be a config file, and I should
> install the package or set CMAKE_PREFIX_PATH. But this wouldn't help,
> because actually the Find-module is missing, because in some way the
> buildsystem expects something wrong.
> So when I (as user) would assume the package is not installed because the
> config has not been found, I would be wrong, but I couldn't see this from
> the code.
> If config-file searching would have to be enabled, I would know from the
> error message (which would then say "Find-module not found") that the
> buildsystem is broken, and not some package is missing or
> CMAKE_PREFIX_PATH is not set.

IOW: it's a quite common error to install a FindFoo.cmake as part of the 
package Foo into the prefix where foo is installed.

So if cmake knows that really the Find-module should have been found, it can 
produce a very clear error message that the missing Find-module must be part 
of the project itself or provided by another previously found package, and 
that the buildsystem is broken.

Alex