diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/typecheck/TcRnDriver.hs | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/compiler/typecheck/TcRnDriver.hs b/compiler/typecheck/TcRnDriver.hs index 63fe36d2c8..d20d43affb 100644 --- a/compiler/typecheck/TcRnDriver.hs +++ b/compiler/typecheck/TcRnDriver.hs @@ -1692,8 +1692,12 @@ check_main dflags tcg_env explicit_mod_hdr ; root_main_id = Id.mkExportedVanillaId root_main_name (mkTyConApp ioTyCon [res_ty]) ; co = mkWpTyApps [res_ty] - ; rhs = mkHsDictLet ev_binds $ - nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) main_expr + -- The ev_binds of the `main` function may contain deferred + -- type error when type of `main` is not `IO a`. The `ev_binds` + -- must be put inside `runMainIO` to ensure the deferred type + -- error can be emitted correctly. See Trac #13838. + ; rhs = nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) $ + mkHsDictLet ev_binds main_expr ; main_bind = mkVarBind root_main_id rhs } ; return (tcg_env { tcg_main = Just main_name, |