Observation on Hadrian's relative performance re current buildsystem

[Ben Gamari]

Herbert Valerio Riedel <hvriedel at gmail.com> writes:

> Hi Malcolm,
>
> On 2017-11-18 at 11:09:28 +0000, Malcolm Wallace wrote:
>
> [...]
>
>> But surely the timing for a full build from scratch is not the most
>> important thing to compare?  In my work environment, full builds are
>> extremely rare; the common case is an incremental build after pulling
>> changes from upstream.  Is this something you can measure?
>
> If Hadrian is more exact about the dependency tracking, I'd expect
> something close to a full rebuild when I `git pull` from GHC HEAD, since
> the Git commit and the snapshot versioning we infer from that,
> pervasively transcends most most artifacts of GHC, and in general you
> should boot & configure everytime you `git pull` unless you're sure it
> won't matter.
>
To be honest, I'm hoping that we can make this less necessary in the
future. Relatively few changes really require a re-`configure`. In my
experience most changes that current demand reconfigure are in .in
files. In these cases I often just hack the changes in to the generated
files myself. In principle there is no reason why Hadrian couldn't do
this as well. I opened #416 to track this some time ago.

Cheers,

- Ben


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