8.8.x change in lookupModule / findModule semantics?

[Daniel Gröber]

Hi,

On Thu, Feb 27, 2020 at 08:02:16AM +0000, Tseen She wrote:
> I think we might be mixing up the two threads here, please let me know if
> I've misunderstood

Ah yes, I was reading both threads and ended up replying to the wrong one
:)

> so I'll respond as if this was in response to the
> thread about in-memory buffers: the function you've hightlighted is working
> as intended (thanks for clarifying the API change, I had to work that out
> myself and was just guessing) and produces the minimal buffer that is then
> used by the next function.

You know, it does look like you're implementing in importsOnly is very
simmilar to ghc's internal getPreprocessedImports. While that function
isn't exported it's just a simple wrapper around HeaderInfo.getImports
which is. You might want to use that API instead or is there a reason you
had to reimplement all of it?

Anyways, looking at the code for parseModule as long as the ModSummary you
pass in has ms_hspp_buf set it should use the buffer instead of the
file. The code will eventually call `hscParse'` which has:

    let src_filename  = ms_hspp_file mod_summary
        maybe_src_buf = ms_hspp_buf  mod_summary

    --------------------------  Parser  ----------------
    -- sometimes we already have the buffer in memory, perhaps
    -- because we needed to parse the imports out of it, or get the
    -- module name.
    buf <- case maybe_src_buf of
               Just b  -> return b
               Nothing -> liftIO $ hGetStringBuffer src_filename

typecheckModule will just use the ParsedSource parseModule produced so it
shouldn't do any more file reading.

> As to the relation between importsOnly and lookupModule / findModule, they
> are independent.

I'm not actually seeing any calls to {lookup,find}Module in your code so
it's very hard to say if the behaviour changed. Do you have a reproducer
for that?

--Daniel
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