[cmake-developers] [CMake] Forwarding parameters to cmake through cmake-gui

[Matthew Woehlke]

On 2013-11-04 15:47, David Cole wrote:
>> My question is still not answered completely:
>>
>> When should the new variable be added? On startup is not really
>> possible because it might be the case that your src/binary directory
>> is not set properly.
>>
>> So you would agree that it makes sense to do it "on configure" but
>> only if the cache is empty? This will not allow to overwrite the
>> variable via parameter but I guess that usecase is not very
>> common?
>
> On startup is the only time it does make sense. After that, the user
> should be in charge, and the command line settings should not be
> re-applied again after a user makes an edit. You don't need the
> src/binary directories set properly necessarily in order to add a cache
> entry to the UI.

There are two mostly separate issues here.

As far as the bug, the ccmake behavior is (IMO, but seems generally 
shared) is just wrong. physhh's questions (above) don't apply to this 
case because there is no concept of interactively selecting the build 
directory in ccmake. So fixing this is, if not easy, at least easy to 
understand how it should behave.

As far as cmake-gui, there are no backward compatibility issues because 
right now it just doesn't support -D at all.

It does however get more complicated...

- What should happen with a -D option if there is not initially a build 
directory selected?

- What should happen if the wrong build directory is initially selected 
and subsequently changed? It seems non-desirable here to forget -D 
(etc.) entirely at that point.

> ccmake and cmake-gui *should* behave (in *my* opinion) as follows:
> - on startup, load the CMakeCache.txt values (if there are any) from the
> previous run
> - then apply the -D arguments so that any -D arguments given on the
> command line overwrite previous cache entries (just like command line
> cmake does already)
> - then put the user in charge and wait for user input

I suppose if I were writing the patch, I would have cmake-gui remember 
whatever -D/-U/etc. options are given and apply them to any build 
directory when it is selected, after loading the cache (if any). But 
*don't* pass them on the cmake (except inasmuch as the initial cache 
will contain them, modulo any changes the user made in the mean time).

IOW, if I specify a -D to cmake-gui, change that value, then change to 
some other build directory, that -D would reset to the value from the 
command line. This is consistent with the current behavior that any 
other changes to the cache of the initial build directory are also lost.

Hmm... a corner case comes to mind, however; if I configure build 
directory A after changing a -D value, then switch to build directory B, 
then back to A, I probably don't want to reapply the -D. So maybe 
cmake-gui would keep track of what build directories have been 
configured in that instance and not apply -D/etc. to them. (However, 
it's probably not very common for that to happen.)

Make sense?

-- 
Matthew