[Haskell-cafe] [Haskell-community] technical thoughts on stack

Patrick Pelletier code at funwithsoftware.org
Thu Sep 15 06:22:42 UTC 2016

On 9/14/16 10:39 PM, Michael Snoyman wrote:
> On Thu, Sep 15, 2016 at 8:25 AM, Patrick Pelletier 
> <code at funwithsoftware.org <mailto:code at funwithsoftware.org>> wrote:
>     On 9/14/16 9:26 PM, Michael Snoyman wrote:
>         I can give more technical details on warning output: it's
>         purely an issue of compromise between many different (and
>         annoying) ways of displaying things. Firstly, the behavior
>         Chris Allen is commenting: if there is a single local target
>         package that you're building, then all of its GHC output is
>         displayed to the console, including warnings.
>     AFAIK, this behavior is not clearly documented.
> I'd be happy to add a comment. Do you have a recommendation of 
> somewhere to put such an explanation that would make sense?

Probably either in:




or both.

>         3. Save the output to a log file, and then display all of the
>         log files to the user at the end, which would result in
>         looking for a needle in a haystack in many cases
>     Is there any harm in having an option for this?  If the number of
>     local packages is small (3 in my case) and there are not a huge
>     number of warnings, this still seems quite manageable.
> Perhaps a simple option to --dump-log-output, which at the end of a 
> build prints all logs from all local packages? That's certainly 
> possible, though I haven't touched that part of the code in quite a while.

Yes, that would at least meet my needs.

>         When I put together the initial code for running builds, I
>         chose (1), which we still have today. It may be interesting to
>         note that I did this mostly based off of my experience with
>         cabal-install doing the same thing (whenever possible, I
>         defaulted with cabal-install behavior, since it got many
>         things right, and regardless is what people were used to).
>     I'm used to using "cabal sandbox add-source" to add dependencies
>     that I have locally checked out (e. g. because I've modified them,
>     or because they aren't released on Hackage yet).  cabal doesn't
>     printing warnings for those dependencies, but it does always print
>     warnings for the one package that I'm working on.  (The one in the
>     current directory.)
>     As far as I know, stack doesn't make a distinction between "the
>     package I'm working on now" and other dependencies which are
>     checked out locally.  They all go in "packages" in the stack.yaml.
>     So, although it's not an apples-to-apples comparison, it is
>     different behavior than I was getting with my cabal workflow.
> There is the extra-dep field in packages, but it wouldn't affect this 
> specific case.

Right.  My understanding is that extra-dep is for packages to fetch from 
Hackage that are outside the current resolver.  (Cabal doesn't really 
have an equivalent option, since its implicit resolver is "everything in 
hackage.")  On the other hand, "cabal sandbox add-source" is for 
packages on the local filesystem.

> But really, the way you tell Stack "the package I'm working on now" is 
> by specifying it as a target on the command line, which _does_ work: 
> `stack build http-client-tls` in my example above does in fact display 
> the output on the console.

Thanks!  That (along with the tip about --pedantic) is good to know.


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