--no-main is deprecated #837

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1. sol commented on May 18, 2023

   

   sol

   on May 18, 2023

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   Is the issue, that you want to load both the test suite and an executable into a GHCi session?

   If yes, you can put the main of your executable into a driver module like so: https://github.com/sol/markdown-unlit/blob/main/driver/Main.hs

   It should then be possible to load everything into GHCi, except for that driver module.

   If this doesn't work, can you share more details about your exact setup?

   Do you currently run your tests with ghcid?

   Other things that might be relevant:

   • https://hspec.github.io/hspec-discover.html#spec-hooks
   • https://github.com/hspec/sensei
2. supki commented on Oct 31, 2024

   

   supki

   on Oct 31, 2024

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   So, I'm also interested in the alternative to --no-main.

   My usual setup includes a library in src/ and a test-suite in test/ that depends on this library. For some projects, I have to perform certain setup rituals before the tests have any chance to run successfully. These generally amount to a variation of main = bracket_ acquireResources releaseResources (hspec spec) which goes to test/Main.hs which is now the main-is module of the test-suite.

   Now, I'd like to load the test-suite in ghci. Previously, I used stack exec -- ghci test/Main.hs for this, which actually works surprisingly well most of time and doesn't require --no-main at all. Unfortunately, it actually works a bit too well, leading to minor inconsistencies between ghci and hls (and other tooling) that are mildly annoying. But, if I use stack ghci package:lib package:test:spec (which in my experience is less inconsistent with hls), then running main understandably results in Ambiguous occurrence ‘main’, which then means I need the --no-main option.

   I briefly skimmed https://hspec.github.io/hspec-discover.html#spec-hooks and I think it might be a solution to my problem, but I'd rather not add more magic to my tests, there is usually enough as it is :)

   Sorry for the essay; I'd just be sad to see --no-main go away, I found it to be a useful option. :)
3. sol commented on Nov 7, 2024

   

   sol

   on Nov 7, 2024

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   @supki it's still not clear to me what exact code layout you're using.

   Previously, I used stack exec -- ghci test/Main.hs for this, which actually works surprisingly well most of time and doesn't require --no-main at all.

   1. Where exactly would you put your custom setup in this scenario? Can you provide example code?

   if I use stack ghci package:lib package:test:spec (which in my experience is less inconsistent with hls), then running main understandably results in Ambiguous occurrence ‘main’, which then means I need the --no-main option.

   1. Where is the second main defined? Again, can you provide example code?
   2. Personally, I prefer stack exec -- ghci / cabal exec -- ghci over stack ghci / cabal repl in most situations.
4. supki commented on Nov 7, 2024

   

   supki

   on Nov 7, 2024

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   Yeah, sure, I actually noticed the warning while working on https://github.com/supki/relocant. The project uses a typical layout (for me). It is pretty small so I think it can be used as an example as is.

   The setup is in https://github.com/supki/relocant/blob/ac9032c4c0ec2e2b1aa1686d8a2ebb7305f975d1/test/Main.hs. This module defines main and is the entry point into the test-suite (https://github.com/supki/relocant/blob/ac9032c4c0ec2e2b1aa1686d8a2ebb7305f975d1/package.yaml#L89). The Spec module (https://github.com/supki/relocant/blob/ac9032c4c0ec2e2b1aa1686d8a2ebb7305f975d1/test/Spec.hs) requires -optF --no-main for me to be able to run :main after stack ghci relocant:lib relocant:test:spec.

   (I generally agree on stack exec -- ghci, but that just trades one set of annoyances for another (e.g., ghci defaulting to -XGHC2021 recently))
5. sol commented on Nov 8, 2024

   

   sol

   on Nov 8, 2024

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   I'm still confused why this wouldn't work.

   Can you please try:

   $ stack ghci relocant:lib relocant:test:spec
   ghci> :module Main
   ghci> main

   1. Does this work?
   2. Can you try if there are any differences between :main and main in that regard?
   3. Also, can you check the output of :show imports?
6. supki commented on Nov 8, 2024

   

   supki

   on Nov 8, 2024

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   1. It does.
   2. Both work, I don't see any differences, but I also don't use :main much beyond the --match option. It seems unlikely that some specific functionality is broken but not :main itself? I'm not sure.
   3. Here's the log:

   %  stack ghci relocant:lib relocant:test:spec --ghci-options -ignore-dot-ghci
   ...
   ghci> :show imports
   import Meta_relocant
   import Paths_relocant
   import Relocant
   import Relocant.App
   import Relocant.App.Env
   import Relocant.App.Log
   import Relocant.App.Opts
   import Relocant.App.Opts.Fmt
   import Relocant.App.Opts.Internal
   import Relocant.App.Opts.Option
   import Relocant.App.ToText
   import Relocant.App.ToTextSpec
   import Relocant.Applied
   import Relocant.AppliedSpec
   import Relocant.At
   import Relocant.Checksum
   import Relocant.Content
   import Relocant.DB
   import Relocant.DB.Table
   import Relocant.Duration
   import Relocant.DurationSpec
   import Relocant.ID
   import Relocant.Merge
   import Relocant.MergeSpec
   import Relocant.Name
   import Relocant.Script
   import Relocant.ScriptSpec
   import Spec
   import SpecHelper.DB
   :module +*Main -- added automatically
   ghci> :module Main
   ghci> :show imports
   import Main
   import Prelude -- implicit
   

   So, not exactly convenient as a solution, but it can be used as a fallback, if --no-main disappears tomorrow.
7. sol commented on Nov 8, 2024

   

   sol

   on Nov 8, 2024

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   OK, at least it's now clear what's happening.

   stack ghci imports all your modules unqualified. That's why both Main.main and Spec.main are in scope, resulting in the name clash.

   As a workaround you have the following options:

   1. Use --no-main, which is deprecated. I am not in a rush to remove it, but I am also not eager to jump through hoops if it gets inconvenient.
   2. Use Main.main instead of main (this will probably not work with :main, but you could use System.Environment.withArgs [...] Main.main if you're inclined)
   3. Initially issue :module Main. This should survive a :reload, so you will only have to issue it once. It should also be possible to add it to a project local .ghci file.

   But what I really recommend is adding something along the lines of:

   -- file test/SpecHook.hs
   module SpecHook where
   
   import Test.Hspec
   import Control.Exception (bracket_)
   import SpecHelper.DB qualified as DB
   
   withTemplate :: IO () -> IO ()
   withTemplate = bracket_ DB.createTemplate DB.dropTemplate
   
   hook :: Spec -> Spec
   hook = aroundAll_ withTemplate

   This approach also has the advantage that e.g. --dry-run does not hit the database.

   👍React with 👍1Reacted by Matvey Aksenov