[Haskell-cafe] Cabal install fails, don't understand why

[Volker Wysk]

Hi, Brandon!

That's some interesting information...

Am Freitag, dem 29.03.2024 um 12:05 -0400 schrieb Brandon Allbery:
> The short version is what Francesco said. The longer version is that with
> modern cabal (and stack), libraries are managed by cabal/stack and you
> don't normally install them directly. 

My case is this. I've written a new version of the HsShellScript library,
and have uploaded it to Hackage. Now I wanted to use it to compile a script
(written in Haskell). I though it wouldn't hurt to install it, so the new
version is available. 

Now I understand that all I had to do is "cabal update", so the new
version's on cabal's radar. The new version would then be downloaded and
compiled automagically.

> For the cases where you need a library to be available outside cabal's
> implicit sandboxing, there is `cabal install --lib`; but be aware that
> multiple versions of packages in the resulting environment may cause other
> build problems down the line, and it's on you to manage the environment
> file as needed. 

Hmm... I've googled what that "environment file" is:
https://ghc.gitlab.haskell.org/ghc/doc/users_guide/packages.html#package-environments

I certainly don't want to manage it by hand.

> The proper way to work with libraries outside of a project is "cabal repl"
> or "stack ghci" as appropriate. For quick one-offs with cabal, you can use
> e.g. `cabal repl -b HsShellScript`. (I don't know the stack equivalent,
> sorry.)

What do you mean by "libraries outside of a project"? The library is one
project by itself. I don't (?) have any libraries outside of projects (that
I know of).

> This whole rigmarole is intended to avoid situations where multiple
> versions of libraries are in ghc's environment and it picks inconsistent
> versions, leading to the old "cabal hell".

I don't want to go there!!  ;-)

Thanks for your explanation. Now the question is: How do I get back to the
normal/regular state, without any library outside of a project? The next
version of my library will sure come...

Cheers, 
Volker


> On Fri, Mar 29, 2024 at 9:50 AM Volker Wysk <post at volker-wysk.de> wrote:
> > Am Freitag, dem 29.03.2024 um 14:36 +0100 schrieb Francesco Ariis:
> > > Hello Volker,
> > > 
> > > Il 29 marzo 2024 alle 14:26 Volker Wysk ha scritto:
> > > > Hi
> > > > 
> > > > I've migrated my HsShellScript library to Cabal 3.0 and now I get an
> > > > error
> > > > when I try to install it:
> > > > 
> > > > -----snip-----
> > > > desktop /usr/local/src/hsshellscript $ cabal install --user
> > > > Wrote tarball sdist to
> > > > /usr/local/src/hsshellscript/dist-newstyle/sdist/hsshellscript-
> > > > 3.6.0.tar.gz
> > > > Resolving dependencies...
> > > > Error: cabal: Cannot build the executables in the package
> > > > hsshellscript
> > > > because it does not contain any executables. Check the .cabal file
> > > > for the
> > > > package and make sure that it properly declares the components that
> > > > you
> > > > expect.
> > > > -----snip-----
> > > 
> > > If you are trying to install a library, use
> > > 
> > >      cabal install --lib
> > > 
> > > and let us know if it worked as you expected
> > 
> > The install succeeds with "--lib". It had to be something stupid. It's
> > been
> > three years since I used cabal and meanwhile things look like they moved
> > forward.
> > 
> > There are other errors, but they don't look cabal-related.
> > 
> > Thanks for your help.
> > 
> > Volker
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> 
> -- 
> brandon s allbery kf8nh
> allbery.b at gmail.com