ConstPtr lost in stub generation

I am transitioning the tree-sitter bindings from ccall to capi and I observe that with the following header:

const char* ts_language_symbol_name(const TSLanguage*, TSSymbol);

and foreign import declaration:

foreign import capi unsafe "tree_sitter/api.h ts_language_symbol_name" 
  ts_language_symbol_name :: ConstPtr Language -> TSSymbol -> IO CString

I get the following warning message

/tmp/ghc2287359_0/ghc_6.c:12:139: error:
     warning: returning 'const char *' from a function with result type 'char *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
       12 | char* ghczuwrapperZC2ZCtreezmsitterzm0zi9zi0zi3zminplaceZCTreeSitterziLanguageZCtszulanguagezusymbolzuname
            (void* a1, HsWord16 a2) {return ts_language_symbol_name(a1, a2);}
          |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The void* a1 is particularly worrying. I can't explain it.

Repro

1. git clone --recursive https://github.com/Kleidukos/haskell-tree-sitter and checkout commit https://github.com/Kleidukos/haskell-tree-sitter/commit/c156f5d26ee728930407d324cf538bc74ccbe58b
2. Run cabal build tree-sitter
3. Observe.