[Haskell-cafe] Cabal: other-modules necessary?

[Volker Wysk]

Hi!

Am Freitag, dem 16.09.2022 um 12:12 +0300 schrieb Oleg Grenrus:
> Also even locally, when you depend on the library and try to link you'll
> get linker errors as omitted modules are not part of linkage.
> 
> Write a test-suite for your library, and you'll notice!

I'm not writing a library here, but several executables. And it works,
without specifying "other-modules". 

But I guess you're right when a library is to be compiled.

Bye,
Volker

> For example, if I comment out other-modules in postgresql-simple and try
> to run a test-suite named "test"
> 
> cabal run test
> 
> I'll get (just) a warning when compiling the library
> 
> <no location info>: warning: [-Wmissing-home-modules]
>     These modules are needed for compilation but not listed in your
> .cabal file's other-modules:
>         Database.PostgreSQL.Simple.Compat
>         Database.PostgreSQL.Simple.HStore.Implementation
>         Database.PostgreSQL.Simple.Internal.PQResultUtils
>         Database.PostgreSQL.Simple.Time.Implementation
>         Database.PostgreSQL.Simple.Time.Internal.Parser
>         Database.PostgreSQL.Simple.Time.Internal.Printer
>         Database.PostgreSQL.Simple.TypeInfo.Types
> 
> but compilation of test-suite fails (it uses TemplateHaskell, otherwise
> it probably would fail when linking the executable)
> 
> <command line>: can't load .so/.DLL for:
> /code/public-haskell/postgresql-simple/dist-newstyle/build/x86_64-linux/ghc-8.6.5/postgresql-simple-0.6.4/build/libHSpostgresql-simple-0.6.4-inplace-ghc8.6.5.so
> (/code/public-haskell/postgresql-simple/dist-newstyle/build/x86_64-linux/ghc-8.6.5/postgresql-simple-0.6.4/build/libHSpostgresql-simple-0.6.4-inplace-ghc8.6.5.so:
> undefined symbol:
> postgresqlzmsimplezm0zi6zi4zminplace_DatabaseziPostgreSQLziSimpleziInternalziPQResultUtils_zdwfinishQueryWith_closure)
> 
> What is additionally annoying, is that if your executable doesn't
> actually (even transitively) use any symbols from other-modules (which
> some test-suites may not), they won't be needed for linking and it will
> succeed... until you add something, and linking will fail with
> incomprehensible error like above.
> 
> - Oleg
> 
> On 16.9.2022 11.53, Nicolas Trangez wrote:
> > Hello Volker,
> > 
> > Compilation will, indeed, succeed. However, distribution won't: if the
> > module is not listed in `Other-Modules` (or any of the other sections),
> > it won't be included in the tarball generated when you invoke `cabal
> > sdist`, i.e., the source archive uploaded to Hackage.
> > 
> > Hence, if someone then tries to download and build your package from
> > Hackage, this will fail, since some module source files are missing.
> > 
> > There may be other effects of not listing some module, though above is
> > the one I'm aware of.
> > 
> > Cheers,
> > 
> > Nicolas
> > 
> > On Fri, 2022-09-16 at 10:47 +0200, Volker Wysk wrote:
> > > Hi
> > > 
> > > The cabal user guide says (in section 6.2.12): "Every module in the
> > > package
> > > must be listed in one of other-modules, library:exposed-modules or
> > > executable:main-is fields."
> > > 
> > > However, I only get a warning message, when I comment out the other-
> > > modules
> > > field in my .cabal file. The program compiles. This is the message:
> > > 
> > > <no location info>: warning: [-Wmissing-home-modules]
> > >     These modules are needed for compilation but not listed in your
> > > .cabal 
> > >     file's other-modules: 
> > >         Hsskripte Sicherung SicherungAktionen Text Wahl Zeit
> > > 
> > > Is it really necessary to specify all the imported modules? If so,
> > > why does
> > > the program compile? Can that warning message be turned off?
> > > 
> > > Apart from that, I'm happy with cabal.   :-)
> > > 
> > > Cheers,
> > > Volker
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