Hindent introduces parse errors in constraints for a default method

[JustusAdam]

Hindent misformats the end of a long constraint section in default method signatures in type class declarations.

I've had this happen in multiple type class declarations, here's just one example

class HasEnvExpr m =>
      MonadRecordEnvExpr m
    where
    addEnvExpression :: EnvExpr m -> m HostExpr
    default addEnvExpression :: ( MonadTrans t
                                , Monad n
                                , MonadRecordEnvExpr n
                                , t n ~ m
                                , EnvExpr m ~ EnvExpr n
    ) => -- <- this is outdented too much. This is a parse error for GHC
        EnvExpr m -> m HostExpr

[michalrus]

Any progress with this? Or maybe how to avoid that? I guess turning it off for a fragment would help, cf.

• Turn off Hindent #466
• Feature request: turning it off for a fragment #442

[michalrus]

For the time being, we’re running this after Hindent…

#!/bin/sh

set -o errexit

cd -P -- "$(dirname -- "$0")"

# <https://github.com/chrisdone/hindent/issues/492>
if [ "$1" = "backend-common/src/Backend/Log/Class.hs" ] ; then
  sed 's/^  ) =>/  \0/' -i "$1"
fi

[toku-sa-n]

While the current master no longer raises a parse error, it fails to align the indent. Below is the current output against the given input.

class HasEnvExpr m =>
      MonadRecordEnvExpr m
  where
  addEnvExpression :: EnvExpr m -> m HostExpr
  default addEnvExpression :: ( MonadTrans t
                              , Monad n
                              , MonadRecordEnvExpr n
                              , t n ~ m
                              , EnvExpr m ~ EnvExpr n
                              ) =>
    EnvExpr m -> m HostExpr

It aligns parameters if the signature is outside of a class declaration.

addEnvExpression ::
     ( MonadTrans t
     , Monad n
     , MonadRecordEnvExpr n
     , t n ~ m
     , EnvExpr m ~ EnvExpr n
     )
  => EnvExpr m
  -> m HostExpr