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Eval plugin errors on :seti #5144
Description
Your environment
Which OS do you use? Up-to-date ArchLinux
Which version of GHC do you use and how did you install it? 9.14.1 from GHCup
How is your project built (alternative: link to the project)? The project is https://github.com/haskell/text
Which LSP client (editor/plugin) do you use? Vim + YCM
Which version of HLS do you use and how did you install it? HEAD
Have you configured HLS in any way (especially: a hie.yaml file)? No
Steps to reproduce
- Clone https://github.com/haskell/text
- open https://github.com/haskell/text/blob/5f948615af326db15ae1757246c4e9d532daf093/src/Data/Text/Lazy.hs#L2000
- trigger the eval plugin
Expected behaviour
Nothing in the file should change (meaning all >>> produce the expected output).
Actual behaviour
You get this:
-- >>> revChunks ["one", "two"]
-- Couldn't match expected type `Text' with actual type `[Char]'
-- In the expression: "two"
-- In the first argument of `revChunks', namely `["one", "two"]'
-- In the expression: revChunks ["one", "two"]
-- Couldn't match expected type `Text' with actual type `[Char]'
-- In the expression: "one"
-- In the first argument of `revChunks', namely `["one", "two"]'
-- In the expression: revChunks ["one", "two"]
--
-- >>> revChunks ["one"]
-- Couldn't match expected type `Text' with actual type `[Char]'
-- In the expression: "one"
-- In the first argument of `revChunks', namely `["one"]'
-- In the expression: revChunks ["one"]
--
-- >>> revChunks [""]
-- Couldn't match expected type `Text' with actual type `[Char]'
-- In the expression: ""
-- In the first argument of `revChunks', namely `[""]'
-- In the expression: revChunks [""]
--
-- >>> revChunks []
-- ""(see no error on the last snippet because it doesn't use "" as a Text) and, after the setup code,
https://github.com/haskell/text/blob/5f948615af326db15ae1757246c4e9d532daf093/src/Data/Text/Lazy.hs#L305-L310
you get this added
-- unknown command 'seti'Changing
https://github.com/haskell/text/blob/5f948615af326db15ae1757246c4e9d532daf093/src/Data/Text/Lazy.hs#L310
to
-- >>> :set -XOverloadedStrings
fixes the issue, which I think reveals that the eval plugin is simply not contemplating :seti.
Activity
dschrempf commentedon Oct 13, 2026
Is this new? Did my recent PR affect this? #4963
Aster89 commentedon Oct 13, 2026
No, you just merged 2 days ago, right? My first experience with the described issue is from 2 weeks ago or so, as testified by haskell/text#711 (review).
dyniec commentedon Oct 15, 2026
It might be the same core issue as in #1817, that is eval plugin sometimes doesn't support ghci commands