Suggestion re altering the build system

[Manuel M T Chakravarty]

Simon Marlow wrote,
> Simon Peyton-Jones wrote:
>> | I understand that incremental builds are more tricky, but during
>> | teaching session I often have only 2 hours to hack on a day.
>>
>> I'm still hopeful that a "last-good-build" date or 
>> signature-of-some-kind should do the job.  Ideally it goes like this
>>
>> * Look at GHC dev wiki, get last-good-build signature
>> * darcs pull -a -upto sig
>> * make
>>
>> I'm thinking that "sig" could be a date-and-time, which you copy/paste 
>> from the wiki into the darcs command.
>>
>> Or am I being naive?
> 
> date/time doesn't work well with darcs.  Consider the case where we have 
> a successful build on date T, and then someone sent us a patch P that 
> they recorded before T.  We push the patch, and now "all the patches up 
> to date T" includes P, but it didn't when we did the build.  This is why 
> we need full tags or contexts to identify the contents of the tree.

Yes, it has to be tags.  And it need to be tags that are in the ghc repo 
*and* all core packages.  (As those not being in sync is a common problem.)

Manuel