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Summary

Running :set -XTemplateHaskell in ghci (in some situations) has two side effects:

1. The scope is cleared
2. Any modules that were specified on the command line are unloaded

While (1) is inconvenient, I have a hard time considering (2) as acceptable.

This also breaks doctest.

I haven't been able to reproduce the issue without cabal exec (e.g. with a .ghc.enviroment-file). Not exactly sure what's the difference.

From the ghci output

package flags have changed, resetting and loading new packages...

I guess that it's somehow related to this code: https://gitlab.haskell.org/ghc/ghc/-/blob/master/ghc/GHCi/UI.hs#L3120

Steps to reproduce

Given:

-- foo.cabal
cabal-version: 3.6
name:           foo
version:        0.0.0
library
  build-depends: base

-- Foo.hs
module Foo where
foo :: Int
foo = 23

Run:

$ cabal build . && cabal exec ghci Foo.hs 
ghci> foo
23
ghci> :set -XTemplateHaskell
package flags have changed, resetting and loading new packages...
ghci> foo

Expected behavior

foo should still be in scope:

ghci> foo
23

Actual behavior

foo is not in scope:

ghci> foo

<interactive>:3:1: error: Variable not in scope: foo

Environment

• GHC version used: 9.2.1

$ cabal --version && uname -s -m
cabal-install version 3.6.2.0
compiled using version 3.6.2.0 of the Cabal library 
Linux x86_64