Spurious recompilations when using a compiler plugin

[George Colpitts]

is it possible that this is also connected to
https://ghc.haskell.org/trac/ghc/ticket/13604 ?

On Tue, Sep 19, 2017 at 10:00 AM Ben Gamari <ben at smart-cactus.org> wrote:

> Conal Elliott <conal at conal.net> writes:
>
> > It appears that use of GHC plugins causes client code to get needlessly
> > recompiled. (See Trac issues 12567
> > <https://ghc.haskell.org/trac/ghc/ticket/12567> and 7414
> > <https://ghc.haskell.org/trac/ghc/ticket/7414>.) It’s becoming more of a
> > problem for usability of the plugin
> > <http://conal.net/papers/compiling-to-categories> I’ve been developing,
> and
> > I’m wondering what can be done. Some questions:
> >
> >    - Is there any work in progress on fixing this situation?
> >    - Are there serious obstacles to fixing it?
> >    - Do plugin writers or users have any workarounds?
> >
> I think the real question is what sort of interface do plugin authors
> need?
>
> I suspect there are a few distinct tasks here,
>
>  * compute and record module implementation hashes in interface files
>
>  * to include plugin implementation hashes in the recompilation check
>
>  * to provide an interface allowing a plugin to compute a hash of its
>    arguments which can be included into the recompilation check. One way
>    of realising this would be to add a field like the following to Plugin,
>
>        pluginHash :: [CommandLineOption] -> Maybe Fingerprint
>            -- Nothing would denote "always rebuild"
>
>    Would this help in your case?
>
> This would allow us to fix the TH problem in #7277 and fix the plugins
> problem in #7414 and #12567 in a nearly optimal way (assuming the plugin
> author is able to precisely define a hash).
>
> None of this is terribly difficult and given Nick's recent work on his
> row types plugin, it seems like it's getting more urgent.
>
> Cheers,
>
> - Ben
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