[Vm-dev] tty's hypothesis on configH in CMakeVMMaker

[David T. Lewis]

On Mon, Jun 16, 2014 at 09:31:13AM -0700, Eliot Miranda wrote:
>  
> On Mon, Jun 16, 2014 at 3:33 AM, Igor Stasenko <siguctua at gmail.com> wrote:
> 
> >
> > Yes, config.h is a leftover of old make process which i had to port over
> > to cmake build process without need to do big changes in source code.
> > I am strong opponent of idea that configuration variables shall
> > automatically , dynamically and implicitly change depending on where you
> > compiling the code. Configuration , as a whole can change, but not its
> > variables.
> > They must be defined once and stay same regardless of building environment.
> >
> > That gives you a better chances that software which you successfully built
> > using same configuration will work identically no matter who or where is
> > built it.
> > And sure thing, for having variations, you can define own configuration
> > e.g. MyVMWith(orWithout)UUID
> > and use it to compile VM with that flag changed.
> > But as i say, key here that this flag is set by your hand once and
> > forever, not by some pre-build configure script which depends on where it
> > runs on.
> >
> 
> Depends what you're talking about.  In this case some linuxes have
> /usr/include/uuid.h and a program called uuidgen, others have
> /usr/include/uuid/uuid.h and a program called uuidgenerate (let alone other
> unixes).  IMO it is not the business of a VM source generation pass to
> decide this.  It is a compile-time configuration pass.
> 
> The approach of having lots of configurations determined at VM source
> generation time leads to VM source which becomes obsolete, is inflexible,
> is duplicated.  There needs to be a sensible split.  VM generation time is
> not the time to choose things like sets of plugins, particular include file
> locations.  IMO it should only produce a full suite of source.  A build
> directory is the place to decide what plugins to choose etc, allowing
> special configurations for special uses (an embedded device vs a desktop
> OS, etc).  Compile time configuration is the time to choose include files,
> library names etc, etc.
> 

Philosophical points of view aside, I have the uncomfortable feeling that
some (all?) of the people in this discussion may have never bothered to look
at how Ian's CMake build actually works.

To put it simply: It implements the approach that Eliot is trying to advocate.
And it works.

My own personal opinion: Philosophically, I tend to favor Igor's point of view
(put things in the image as much as possible). But in practice, this is a case
where the implementors of CMake are in a better position to deal with platform
differences than we (the Squeak/Pharo community) can afford to do.

Furthermore, the organization that Ian created puts the responsibilities
where they belong, with minor customizations for the various plugins and
modules located in their respective platform source directories where needed,
and overall control of the CMake configuration and build located in a small
set of CMake files.

To speak plainly, I have a hard time understanding why something that is well
designed and implemented by its original author needs to be reengineered and
reimplemented by every new person with a new opinion. Why not just support and
contribute to the original author? What's so difficult about that?

Dave