GHC silently turns off dynamic output, should this be an error?

[Simon Marlow]

On 06/07/2014 12:25, Christopher Rodrigues wrote:
> Investigating #9176 further, GHC does at least three different things
> with imported modules under -dynamic-too compilation.  It probably
> should be changed to handle imports uniformly.  It looks like
> dynamic-too support was bolted on to a system designed for one-pass
> compilation, and I'm not clear on how to restructure it.  Guidance would
> be appreciated, as it would cut down the time I need to figure out how
> the driver works.
>
> Here are the three things that can happen:
>
> 1. When compiling in one-shot mode, with -c, GHC will do what Igloo
> described.  If normal and dynamic interface hashes don't match, it will
> compile the normal way, then compile again the dynamic way.
>
> 2. When compiling with --make and importing from a package, if normal
> and dynamic interface hashes don't match, GHC will disable dynamic-too,
> but it will not restart the pipeline.  Only the normal .hi file is produced.

This does sound wrong.

> 3. When compiling with --make and importing from a non-package module,
> GHC will not check interface hashes.  It will proceed as if normal and
> dynamic interface hashes match.

This might be OK if we have already compiled all the modules in this 
compilation pass.  If some were compiled previously, then it is possible 
that we have some non-matching .hi files, and in that case I think we 
should probably just consider the module out of date and recompile it, 
generating both dynamic and non-dynamic .hi files, which will be 
guaranteed to have the same hash.

Cheers,
Simon