[squeak-dev] Monticello: committing part of a change

Colin Putney colin at wiresong.com
Tue Feb 15 03:54:10 UTC 2011

On Mon, Feb 14, 2011 at 2:24 PM, Frank Shearar
<frank.shearar at angband.za.org> wrote:
> On 2011/02/07 16:06, Chris Muller wrote:

> OK, I see that when one hits the Save button, Monticello creates the new
> version using MCWorkingCopy>>newVersion, which ultimately calls
> MCPackage>>snapshot. This returns an MCSnapshot containing a collection of
> MCDefinitions for all the bits & pieces inside a package - class
> definitions, method definitions, etc.
> So presumably one could save SOME of the pending changes, by simply saving
> an MCSnapshot that contains only SOME of the definitions in a package?

The basic problem here is this: MC works by saving snapshots of
packages. When it loads a snapshot, it makes the code in the package
match what's recorded in the snapshot. That includes *removing* code
that's in the image and part of the package, but not in the snapshot.
So if you have a snapshot that only includes some of the definitions,
when you try to load it, everything else will be deleted.

Now, there's a few ways to work around it, but they all have issues.
One way is to include all the definitions, but only take some of them
from the image, and take the rest from the previous version of the
package. That should get you a complete, but it has a subtler problem:
the code in the "snapshot" never existed in your image. It may not
have enough internal consistency to be loadable. It might have methods
for classes that don't exist, or references to instance variables that
don't exist etc. Rather than deal with all those issues, Monticello
just relies on the regular Smalltalk mechanisms for ensuring that the
system is internally consistent.

Another way would be to create a sort of custom package definition,
which would allow the snapshot to contain just the changes you're
interested in, without wiping out the rest of the package  when you
load it. But then you need a way to manage that package definition, a
way to load it into the image before you load the snapshot, or a way
to bundle into the version file. That's pretty non-trivial - if we had
that, we wouldn't need PackageInfo.

For what it's worth, you can do it in Monticello 2 by creating a
change set before you make the fix, then taking a snapshot of the
change set.


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