Commit 49e423e9 authored by Tao He's avatar Tao He Committed by Ben Gamari

Put the `ev_binds` of main function inside `runMainIO`

This ensures that the deferred type error can be emitted correctly.

For `main` function in `Main` module, we have

    :Main.main = GHC.TopHandler.runMainIO main

When the type of `main` is not `IO t` and the
`-fdefer-type-errors` is enabled, the `ev_binds`
of `main` function will contain deferred type
errors.

Previously, the `ev_binds` are bound to `runMainIO main`,
rather than `main`, the type error exception at runtime
cannot be handled properly. See Trac #13838.

This patch fix that.

Test Plan: make test TEST="T13838"

Reviewers: bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #13838

Differential Revision: https://phabricator.haskell.org/D4708
parent c65159dc
......@@ -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,
......
{-# OPTIONS_GHC -fdefer-type-errors #-}
module Main where
main :: () -> ()
main = undefined
T13838.exe: T13838.hs:6:1: error:
• Couldn't match expected type ‘IO t0’ with actual type ‘() -> ()’
• Probable cause: ‘main’ is applied to too few arguments
In the expression: main
When checking the type of the IO action ‘main’
(deferred type error)
......@@ -130,6 +130,7 @@ test('TypeableEq', normal, compile_and_run, [''])
test('T13435', normal, compile_and_run, [''])
test('T11715', exit_code(1), compile_and_run, [''])
test('T13594a', normal, ghci_script, ['T13594a.script'])
test('T13838', [exit_code(1)], compile_and_run, ['-fdefer-type-errors'])
test('T14218', normal, compile_and_run, [''])
test('T14236', normal, compile_and_run, [''])
test('T14925', normal, compile_and_run, [''])
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