[Vm-dev] Rant about generated files: should they stay in repository?

[Frank Shearar]

We've had this discussion before, in November last year - "VM packaging 
for Cog transition" - starting here: 
http://lists.squeakfoundation.org/pipermail/vm-dev/2010-November/005797.html

frank

On 2011/03/11 11:34, Esteban Lorenzano wrote:
>
> Igor, I'm with you :)
> let's get rid of generated sources from repository!
>
> best,
> Esteban
>
> El 10/03/2011, a las 10:01p.m., Igor Stasenko escribió:
>
>>
>> I am against it , because it is going to nowhere.
>>
>> So let me elaborate...
>>
>> In Cog, we have an image which generating an universal sources for VM
>> on all platforms.
>> These generated files then put under source control.
>>
>> Pros:
>> - to build VM you can just checkout and build
>>
>> Cons:
>> - err , wait.. which exactly VM you going to build? can you use same
>> sources for different builds?
>>
>> Yes, I can use same generated sources for everything, but depending on
>> configuration and/or target operating system i can receive completely
>> different results.
>>
>> Because, for recreating VM as an artifact to reproduce same
>> circumstances as they were (when some bug was triggered) a generated
>> sources snapshot is not enough.
>>
>> Simple example:
>>   - VM compiled for Macs using -O3 optimization are stable.
>> In contrary to linux, where using -O2 with certain files makes your
>> VM crash few (milli)seconds after startup.
>>
>> Second ( i don't like repeating myself but still ;):
>> - the only way to make sure that VMMaker loads into our latest and
>> greatest image(s) and producing same output(s) is to have someone to
>> continuously try load it,
>> then use it to generate sources, then compile the VM and then run
>> tests for that VM.
>> We have a generous guys in our community, who can do that for us. This
>> is a Mr Hudson, and Mr Jenkins that joined party lately.
>>
>> I'd like to stress that generated files are just an intermediate data,
>> which nobody interested in.
>>
>> Because as input what is relevant should be only :
>> - a VMMaker
>> - a platform-specific sources/libs
>> - a build configuration
>>
>> and as output we always have:
>>   - VM
>>
>> what happens in the middle is really unimportant as long as you can
>> guarantee reproducibility of  the same output from same inputs.
>>
>> VM functioning should not depend on some random noise which comes from
>> unrelated sources like
>> - generated source files line ending convention
>> - the date stamp when VM was built
>> - anything which is not listed in the inputs list above
>> and if it does, we should eliminate it.
>>
>> Because if it does, then you don't have a stable builds. And having a
>> snapshot of sources which kinda works and kinda stable
>> worth nothing, because at any moment in ongoing development you can
>> meet same issue which will pop up out of nowhere.
>> And it will pop out exactly because you don't care to always do things
>> from scratch , starting from image and VMMaker.
>> Because it is so convenient to just pull the generated sources from
>> repo and you done.
>> And those silly stupids which trying to use VMMaker are not of your
>> concern.. because when they fail to build stable VM (and they will),
>> you can always tell them that they are using wrong sources and because
>> you can't reproduce it (things is always working well for you, in your
>> warm corner :)
>>
>> So, i think that keeping a generated files works as some kind of
>> defensive policy which doesn't allows you to address certain
>> problems for real.
>> And sure thing, because we are lazy :)
>>
>>
>> --
>> Best regards,
>> Igor Stasenko AKA sig.
>
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