[isabelle-dev] Sane Mercurial history

Makarius makarius at sketis.net
Mon Mar 22 12:38:30 CET 2010

On Wed, 3 Mar 2010, Makarius wrote:

> Dear Isabelle contributors,
> this is a reminder of some basic principles that ensure that our history
> remains manageable.

It seems that a few more words need to be said about producing 
intelligible changesets:

Individual changesets need to be understandable to readers -- both the 
ones who are kind enough to keep an eye on incoming pushes, and the ones 
who need to diagnose problems days/months/years later.

Due to the complexity of the system, changes routinely introduce new 
problems.  By keeping changesets at a reasonable complexity, with not too 
many different things rolled into one, it is later possible to isolate 
critical spots by bisection of the history.  Experienced Mercurial users 
know what I am speaking of.

Typical counterexamples are huge blobs that claim to have "fixed some 
bugs" or have done "major refactoring".  Nobody can digest this. 
Experienced developers know that quite often it is the author himself who 
is suffering most from such unsystematic editing of the sources, because 
isolating problems will require to go through the whole sources again.


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