What changed between GHC 8.8 and 8.10 that could cause this?

ÉRDI Gergő gergo at erdi.hu
Sun Mar 7 03:02:07 UTC 2021

Thanks Matthew and Julian! Unfortunately, trying out GHC before/after this 
change didn't turn out to be as easy as I hoped: to do my testing, I 
need to build a given GHC commit, and then use that via Stack to install 
~140 dependencies so that I can then test the problem I have initially 
seen. And it turns out doing that with a random GHC commit is quite 
painful because in any given Stackage snapshot there will be packages with 
which the GHC-bundled libraries are incompatible... :/

On Thu, 4 Mar 2021, Julian Leviston wrote:

> Hi,I don’t know enough about what Clash does to comment really, but it sounds like
> it’s to do with my work on enabling multiple linker instances
> in https://gitlab.haskell.org/ghc/ghc/-/merge_requests/388 — maybe reading through
> that or the plan I outlined at https://gitlab.haskell.org/ghc/ghc/-/issues/3372 might
> help, though I’m not sure.
> Strange, though, as this work was to isolate state in GHC — to change it from using a
> global IORef to use a per-process MVar . But it definitely did change the way state is
> handled, so it might be the related to these issues somehow?
> I realise this isn’t much help, but maybe it points you in a direction where you can
> begin to understand some more.
> Julian
>       On 4 Mar 2021, at 10:55 pm, ÉRDI Gergő <gergo at erdi.hu> wrote:
> Hi,
> I'm trying to figure out a Clash  problem and managed to track it down to a GHC
> upgrade; specifically, a given Clash version, when based on GHC 8.8, has no
> problem synthesizing one module after another from one process; but the same
> Clash version with GHC 8.10 fails with link-time errors on the second
> compilation.
> The details are at https://github.com/clash-lang/clash-compiler/issues/1686
> but for now I'm just hoping that some lightbulb will go off for someone if some
> handling of internal state has changed in GHC that could mean that the symbol
> tables of loaded modules could persist between GHC invocations from the same
> process.
> So, does this ring a bell for anyone?
> Thanks,
> Gergo
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