Re: Deep vs Shallow trace: Removing the tradeoff?

[Ludovic Courtès]

Hi,

ilmu <ilmu@rishi.is> skribis:

> To drive the point home: If the artefact has the same hash as it did before 
> then clearly the underlying change did not affect it. Early cut-off is 
> therefore not possible in the case where the program being depended on is 
> supposed to be used at runtime.
>
> This is at least how I am thinking about it, I think this would be a good 
> incremental improvement on the state of the art but it would still have these 
> limitations.

What’s currently implemented is memoization: the hash (of the .drv and
that of the output(s)) is computed over all the inputs.

Since the output file name (the one passed to “./configure --prefix” &
co.) appears in the build result 99% of the time, the content vary at
least due to occurrences of the output file name.

Thus, content comparison are not doable as is.  What would help is
content comparison _modulo_ output file name(s).

But again, “same hash as it did before” is a framing that doesn’t hold
in a purely functional, stateless context.

Ludo’.