Add cabal flag and CPP option to use Loc from monad-logger.

[dmjio]

If template haskell is disabled in monad-logger, this needs to
be propagated to persistent. Otherwise, type errors ensue.

Database/Persist/Sql/Raw.hs:43:18: error:
    • Couldn't match type ‘Control.Monad.Logger.Loc’
                     with ‘Language.Haskell.TH.Syntax.Loc’
      NB: ‘Language.Haskell.TH.Syntax.Loc’
            is defined in ‘Language.Haskell.TH.Syntax’
                in package ‘template-haskell-2.14.0.0’
          ‘Control.Monad.Logger.Loc’
            is defined in ‘Control.Monad.Logger’
                in package ‘monad-logger-0.3.30’
      Expected type: Control.Monad.Logger.Loc
                     -> Control.Monad.Logger.LogSource
                     -> Control.Monad.Logger.LogLevel
                     -> fast-logger-2.4.15:System.Log.FastLogger.LogStr.LogStr
                     -> IO ()
        Actual type: LogFunc
    • In the second argument of ‘runLoggingT’, namely
        ‘(connLogFunc conn)’
      In a stmt of a 'do' block:
        runLoggingT
          (logDebugNS (pack "SQL") $ T.append sql $ pack $ "; " ++ show vals)
          (connLogFunc conn)
      In the expression:
        do runLoggingT
             (logDebugNS (pack "SQL") $ T.append sql $ pack $ "; " ++ show vals)
             (connLogFunc conn)
           getStmtConn conn sql
   |
43 |                 (connLogFunc conn)
   |                  ^^^^^^^^^^^^^^^^

Database/Persist/Sql/Raw.hs:65:10: error:
    • Couldn't match type ‘Control.Monad.Logger.Loc’
                     with ‘Language.Haskell.TH.Syntax.Loc’
      NB: ‘Language.Haskell.TH.Syntax.Loc’
            is defined in ‘Language.Haskell.TH.Syntax’
                in package ‘template-haskell-2.14.0.0’
          ‘Control.Monad.Logger.Loc’
            is defined in ‘Control.Monad.Logger’
                in package ‘monad-logger-0.3.30’
      Expected type: Control.Monad.Logger.Loc
                     -> Control.Monad.Logger.LogSource
                     -> Control.Monad.Logger.LogLevel
                     -> fast-logger-2.4.15:System.Log.FastLogger.LogStr.LogStr
                     -> IO ()
        Actual type: LogFunc
    • In the second argument of ‘runLoggingT’, namely
        ‘(connLogFunc conn)’
      In a stmt of a 'do' block:
        runLoggingT
          (logDebugNS (pack "SQL") $ T.append sql $ pack $ "; " ++ show vals)
          (connLogFunc conn)
      In the expression:
        do conn <- projectBackend `liftM` ask
           runLoggingT
             (logDebugNS (pack "SQL") $ T.append sql $ pack $ "; " ++ show vals)
             (connLogFunc conn)
           stmt <- getStmt sql
           res <- liftIO $ stmtExecute stmt vals
           ....
   |
65 |         (connLogFunc conn)
   |          ^^^^^^^^^^^^^^^^

Note: this change will not affect any code by default, only when the flag is disabled.

Before submitting your PR, check that you've:

• Bumped the version number
• Documented new APIs with Haddock markup
• Added @since declarations to the Haddock

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)

[MaxGabriel]

I'm not sure if I'm reading this right, but it kind of looks like Loc is always exported from monad-logger (the fake one if you have template haskell turned off, the TH one if you have it turned one). Could we instead always import Loc from monad-logger, and then we'd just get the correct version depending on what flag you have on monad-logger?

[MaxGabriel]

If I'm correct about that, it should probably be documented in monad-logger that that's the intended approach

[dmjio]

I'm trying to understand exactly why I did this. It does seem that monad-logger exports Loc from either template-haskell or its own defined Loc here. So it seems as if the changes I proposed would be redundant. If that were the case I would not expect the error message above to occur.

I honestly think Loc has the correct type, but for some reason GHC is not allowing the type being exported to be used since it comes from a different package. It would seem that nobody has tried to disable template_haskell in monad-logger and then use persistent with it, but I could be wrong here.

Here is a minimal reproduction (nix-build default.nix) of what I'm experiencing using the latest persistent-2.10.5.2 and monad-logger-0.3.34

# default.nix
{ pkgs ? import <nixpkgs> {} }: # nix rev 96069f7d890b90cbf4e8b4b53e15b036210ac146
with pkgs.haskell.lib;
let
  monad-logger = disableCabalFlag pkgs.haskellPackages.monad-logger "template_haskell";
  persistent = pkgs.haskellPackages.persistent.override { inherit monad-logger; };
in
  persistent

(shows above error)

[MaxGabriel]

Oh, what I think the issue is is that Persistent does not import Loc from monad-logger, it always imports it from template haskell:

persistent/persistent/Database/Persist/Sql/Types/Internal.hs

Line 39 in be8901e

import Language.Haskell.TH.Syntax (Loc)

Would you be able to try Persistent always importing like this:

import Control.Monad.Logger (LogSource, LogLevel, Loc)

and seeing if that compiles for you?

[dmjio]

Nice, worked for both template_haskell enabled and disabled on monad-logger. I reverted the flag stuff, and we can squash the other commits to clean up the history.

[MaxGabriel]

Nice, do you mind adding a note to the changelog file about this?

[dmjio]

Done.

[MaxGabriel]

Thanks, merged! I also added documentation about this to monad-logger

[dmjio]

Awesome, thanks a ton 🍻