Fix a botched log-message

[Aaron Bentley]

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Stuart McGraw wrote:
> Stefan Monnier wrote:
>>>> How can I fix a log-message in some old revision?
>>>> (like "cvs admin -m<rev>:<msg>")
>>> You can't.  History is immutable.
>>
>> This is an annoying limitation.  Botched log messages happen.
>> And since they don't cause mis-compilations, they tend to be
>> discovered late.
>> [...]
> 
> It can be more than annoying.  Imagine if a programmer
> added a log message that contained, for example, a sexually
> harassing comment directed at a coworker.

We refer to scenarios like this as "nuclear launch codes".  Other
examples of things that absolutely must be removed are trade secrets,
source code that is illegally copied, and of course, the launch codes to
a nuclear missile.

http://bazaar-vcs.org/NuclearLaunchCodes

Because Bazaar is a decentralized system, the values it stores must be
immutable.

Bazaar's model currently supports two approaches to this problem:
1. Generate an alternate history in which the offending data was never
entered.
2. Remove the revisions which contained the offending data from storage,
converting them into "ghost revisions".

These are obviously heavy-duty approaches, but can be employed in such
critical situations.

Aaron
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