./hadrian/ghci compilation error that doesn't appear at build time.

Using the ./hadrian/ghci script, I am getting this error:

/home/hecate/Contrib/GHC/ghc/compiler/GHC/Utils/Misc.hs:1214:22: error:
    • Could not deduce (Foldable t0) arising from a use of ‘elem’
      from the context: MonadFail m
        bound by the inferred type of
                   readExp :: MonadFail m => [Char] -> m (Int, [Char])
        at /home/hecate/Contrib/GHC/ghc/compiler/GHC/Utils/Misc.hs:(1214,6)-(1215,49)
      The type variable ‘t0’ is ambiguous
      These potential instances exist:
        instance Foldable (Either a) -- Defined in ‘Data.Foldable’
        instance Foldable Down -- Defined in ‘Data.Foldable’
        instance Foldable Proxy -- Defined in ‘Data.Foldable’
        ...plus six others
        ...plus 44 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: e `elem` "eE"
      In a stmt of a pattern guard for
                     an equation for ‘readExp’:
        e `elem` "eE"
      In an equation for ‘readExp’:
          readExp (e : s) | e `elem` "eE" = readExp' s
     |
1214 |      readExp (e:s) | e `elem` "eE" = readExp' s
     |                      ^^^^^^^^^^^^^

/home/hecate/Contrib/GHC/ghc/compiler/GHC/Utils/Misc.hs:1214:31: error:
    • Could not deduce (IsString (t0 Char))
        arising from the literal ‘"eE"’
      from the context: MonadFail m
        bound by the inferred type of
                   readExp :: MonadFail m => [Char] -> m (Int, [Char])
        at /home/hecate/Contrib/GHC/ghc/compiler/GHC/Utils/Misc.hs:(1214,6)-(1215,49)
      The type variable ‘t0’ is ambiguous
      These potential instances exist:
        instance (a ~ Char) => IsString [a] -- Defined in ‘Data.String’
        ...plus two instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the second argument of ‘elem’, namely ‘"eE"’
      In the expression: e `elem` "eE"
      In a stmt of a pattern guard for
                     an equation for ‘readExp’:
        e `elem` "eE"
     |
1214 |      readExp (e:s) | e `elem` "eE" = readExp' s
     |                               ^^^^
Failed, 28 modules loaded.
(13.35 secs,)

Being perfectly candid, isn't that the kind of things that are supposed to get caught in the CI?