Re: toughts on the :child command

John Williams wrote:

> I've been trying to work out how one might build a large project that uses
> the :child command to combine several recipe files together.  The example
> given in the tutorial involves too much boilerplace code for my liking,
> and the logic just seems a little backwards to me.  Also I'm a little
> constrained in how things work since I'm trying to replace Makefiles for
> some complicated project and I want to keep the functionality as similar
> as possible.
> 
> What I would *LIKE* to do is put a project-wide 'main.aap' in the root of
> the project hierarchy and put a file to build libraries in the 'src/lib'
> directory.  I want the build libraries to go into the 'lib/linux'
> directory.
> 
> --- main.aap ---
> 
> Top = `os.getcwd()`
> LibTop = $Top/lib/linux
> INCLUDES = -I$Top/include
> :child src/lib/child.aap
> 
> --- src/lib/child.aap ---
> 
> :dll $LibTop/foo : foo1.cc foo2.cc
> 
> --- end ---
> 
> Several things about this annoy me.  First, it seems like I shouldn't have
> to set $Top; based on the name, I would have expected $TOPDIR to do this
> for me, but instead it's just the opposite of what I want.  Ideally I'd
> like $Top be expand to a relative path to the top-level directory, so the
> AAP output isn't so verbose, but I can't figure out a clean way to do this. 
> How about creating a new builtin variable that expands to "." in the
> top-level file, "../.." in src/lib/child.app, etc.?  Such a variable
> should probably also have a corresponding Python function just like $TOPDIR
> has topdir().

The $TOPDIR and $CHILDDIR variables were added to allow a child or
grandchild to give file names back to the parent or toplevel recipe,
without the need for the child recipe to know where it's located.  I now
realize that $TOPDIR was not a good name for what it stands for.

What you did with $Top works and I don't see a real problem with it.
Except that it takes a bit of effort to make the paths relative (take
$TOPDIR and replace each part with "..").  Does this happen often enough
to add a feature in Aap for this?  I suppose it does.

What would be good names for these variables?  $PARENTDIR sounds
obvious, but $TOPDIR is confusing.  I think backwards compatibility is
important, thus we can't change the existing $TOPDIR.  $TOPLEVELDIR?
$STARTDIR?  $ROOTDIR?

An alternative would be to provide a function that turns $TOPDIR into
a path with ".." parts.  But that will not be easy to understand.

> My next problem is that the shared library built in src/lib/child.aap
> doesn't get added to the dependencies of the 'all' target.  I could fix
> this by writing my own "all" target like this:
> 
>   all : $LibTop/${DLLPRE}malloc${DLLSUF}
> 
> But that sure is ugly, and it would be a maintenence hassle when I'm
> building a lot of programs or libraries in one project, as often happens
> at my company.

This is a known bug, Adriaan also reported it.  Sorry, didn't get fixed
yet.  You could work around it by adding the target to $AllTarget in the
child recipe:

	child:
		AllTarget += $LibTop/foo
	
	toplevel:
		all : $AllTarget

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