[Haskell-cafe] LTS-10.* missing build-depends suggestion

[Rick Owens]

Thanks for the help/info guys!

On Thu, Jan 25, 2018 at 3:51 AM, Michael Snoyman <michael at snoyman.com>
wrote:

> Nice repro Dan! I hope you don't mind, I took your repro and opened a GHC
> Trac ticket about this:
>
> https://ghc.haskell.org/trac/ghc/ticket/14717#ticket
>
> On Thu, Jan 25, 2018 at 9:29 AM, Dan Burton <danburton.email at gmail.com>
> wrote:
>
>> Hm, you're right. Seems like a GHC thing. I've tested a simple file with
>> "import Data.Map" on both a stack project and a cabal project -- with
>> containers installed in ghc's main package-db, as verified via stack/cabal
>> exec ghc-pkg list containers -- and it doesn't give the hint in either case.
>>
>> Taking it a step further and removing cabal/stack out of the equation...
>>
>> $ cat Main.hs
>> module Main where
>> import Data.Map
>> main = putStrLn "It compiles"
>>
>> $ ghc-pkg list containers
>> /usr/local/Cellar/ghc/8.2.2/lib/ghc-8.2.2/package.conf.d
>>     containers-0.5.10.2
>>
>> $ ghc --make -hide-all-packages -package base Main.hs
>> [1 of 1] Compiling Main             ( Main.hs, Main.o )
>>
>> Main.hs:2:1: error:
>>     Could not find module ‘Data.Map’
>>     Use -v to see a list of the files searched for.
>>   |
>> 2 | import Data.Map
>>   | ^^^^^^^^^^^^^^^
>>
>> $ ghc --make -hide-all-packages -package base -package containers Main.hs
>> [1 of 1] Compiling Main             ( Main.hs, Main.o )
>> Linking Main ...
>>
>> -- Dan Burton
>>
>> On Wed, Jan 24, 2018 at 8:38 PM, Michael Snoyman <michael at snoyman.com>
>> wrote:
>>
>>> FWIW, I've also noticed that with LTS 10/GHC 8.2.2 I no longer get the
>>> package name suggestions, even when I know I have the package installed. I
>>> don't know if it's an issue with Stack or GHC, I haven't investigated. But
>>> I can't think of something on the Stack side which would make the behavior
>>> different between GHC 8.0.2 and GHC 8.2.2.
>>>
>>> On Thu, Jan 25, 2018 at 4:02 AM, Dan Burton <danburton.email at gmail.com>
>>> wrote:
>>>
>>>> I believe the particular feature you are talking about is a feature of
>>>> GHC. Whether a suggestion is show or not merely depends on whether GHC sees
>>>> the package in question in its package database(s).
>>>>
>>>> If you are using stack, then you can look at one of your LTS 9
>>>> projects, and run
>>>>
>>>> stack exec -- ghc-pkg list
>>>>
>>>> In order to see the list of installed packages. (I think something like
>>>> `cabal exec ghc-pkg list` should do the same for a cabal project.)
>>>>
>>>> Identify the packages you tend to use, go into one of your LTS 10
>>>> projects, and `stack install pkg1 pkg2 ...`
>>>>
>>>> Note that with stack, each minor version of LTS has its own package
>>>> database, so packages locally installed into lts-10.1 will not necessarily
>>>> be available in your local instance of lts-10.2. Repeat stack install to
>>>> taste.
>>>>
>>>> tl;dr the trick is to set up your package database so that GHC knows
>>>> what to suggest for you
>>>>
>>>> -- Dan Burton
>>>>
>>>> On Wed, Jan 24, 2018 at 5:12 PM, Rick Owens <rick at owensmurray.com>
>>>> wrote:
>>>>
>>>>> Dear Haskell Café,
>>>>>
>>>>> I am a long-time Haskell developer with a proliferation of private
>>>>> projects. I typically make very heavy use of stack and LTS. Today, I tried
>>>>> to bootstrap my first project using LTS-10.* (with GHC-8.2.2) and I ran
>>>>> into an interesting problem (for me).
>>>>>
>>>>> In the past, with lts-9.* and below, when I started cranking on some
>>>>> code and writing a bunch of imports:
>>>>>
>>>>> > import Control.Monad.Trans.Class (MonadTrans)
>>>>> > import Data.Map (Map)
>>>>>
>>>>> I would try to build first without updating the cabal file
>>>>> build-depends, and I would get something like the following error messages:
>>>>>
>>>>> >   /path/to/Module.hs:48:1: error:
>>>>> >       Failed to load interface for ‘Data.Map’
>>>>> >       It is a member of the hidden package ‘containers-0.5.7.1’.
>>>>> >       Perhaps you need to add ‘containers’ to the build-depends in
>>>>> your .cabal file.
>>>>> >       Use -v to see a list of the files searched for.
>>>>> >
>>>>> >   /path/to/Module.hs:21:1: error:
>>>>> >       Failed to load interface for ‘Control.Monad.Trans.Class’
>>>>> >       It is a member of the hidden package ‘transformers-0.5.2.0’.
>>>>> >       Perhaps you need to add ‘transformers’ to the build-depends in
>>>>> your .cabal file.
>>>>> >       Use -v to see a list of the files searched for.
>>>>>
>>>>>
>>>>> This was good because the error contained a suggested solution which
>>>>> contained the missing package, and I could sort of lazily add the
>>>>> build-depends I needed without having to memorize a (Module -> Package)
>>>>> mapping. I even had developer tooling to do it automatically.
>>>>>
>>>>> With lts-10.*, however, the analogous error message looks like this:
>>>>>
>>>>> > /path/to/Module.hs:9:1: error:
>>>>> >     Could not find module ‘Data.DoubleWord’
>>>>> >     Use -v to see a list of the files searched for.
>>>>> >   |
>>>>> > 9 | import Data.DoubleWord (Word256(Word256), Word128(Word128))
>>>>> >   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>>>>
>>>>> I am wondering, is there a way to bring back the solution suggestion?
>>>>> Not having access to it has made me realize how heavily I was using that
>>>>> feature. What do others think about this missing bit of supplemental error
>>>>> information?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> -Rick Owens
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>
>>>>
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>>>
>>
>
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