Very cool Keith. Does it also fix the problem with method categories?
I would then be able to build the new squeak-dev beta on top of it.

2007/10/2, Keith Hodges <keith_hodges at yahoo.co.uk>:
> I have found the problem which led to packages needing a recompile if
> instance vars are changed significantly. This was leading to image
> crashes when upgrading the dev-image package universes. Recent
> Omnibrowser changes provided a perfect test scenario.
>
> This was our big showstopper bug!
>
> cheers
>
> Keith
>
> =========
> The following is for documentation of the loading process and is a very
> good reason why SystemEditor is much better solution.
>
> The loading process.
>
> [preloadOver:]
>
> When loading classes, first of all MC removes all class extenstions for
> a class and its subclasses, and saves them for later. This avoids
> problems later in the load (see **).
>
> Then MC attempts to change the class to a union of the old and new
> class  definitions in order that as many methods as possible, old and
> new will compile. This change prompts a recompile of the class.
>
> Old methods which happen to use new inst var names for temp's will fail
> to recompile with Syntax Errors. At this stage such SyntaxErrors being
> resumable are ignored.
>
> For each method being added the obsolete method (if there is one) is
> removed.
>
> [*] part of the show-stopping bug was caused by failing to remove the
> obsolete methods at this point. This would cause the next next class
> recompile to fail due to undeclared items in the obsolete methods
>
> When loading methods, each method being added is compiled ready to be
> added later. This compilation may fail if the unioned-class definition
> failed to compile earlier hence the importance of *.
>
> [removal]
>
> Methods that are no longer needed are removed. If the method is an
> '-override' the old method is found and reinstated.
>
> [install]
>
> Loading Classes: The class is then changed to the required definition.
> If  this changes the definition then a recompile will occur again.
> Methods which are not for this class definition and refer to removed
> instVars will fail to recompile at this point. [this used to include
> obsolete methods which were not being removed as indicated above*]
>
> [**] NOTE: At this point class extensions from other packages will fail
> to recompile if they are accessing inst vars directly, and those
> instvars have been removed.
>
> The solution is to to remove extensions first until such time as they
> will recompile or become superseded by  a new method
>
> Loading Methods: if the previous compilation failed, it will be retried
> in the context of the new class definition. The compiled method is added
> to the class and logged to changes
>
> [ postinstall ]
>
> Loading Classes: Class extensions that were removed to begin with are
> re-compiled and installed. Classes effected are recompiled (not sure why
> this is necessary but it is!).
>
> Loading Methods: FFI field definitions are loaded (first) and
> #initialize is run (last)
>
> [ postLoad ]
>
> Loading Classes:
>     Restored class extension methods have their observers notified.
>
> Loading Methods:
>     Methods have their observers notified.
>
>


-- 
Damien Cassou