[Git][ghc/ghc][master] Don't suppress *all* Wanteds
Marge Bot (@marge-bot)
gitlab at gitlab.haskell.org
Fri Mar 3 03:42:24 UTC 2023
Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
1ed573a5 by Richard Eisenberg at 2023-03-02T22:42:06-05:00
Don't suppress *all* Wanteds
Code in GHC.Tc.Errors.reportWanteds suppresses a Wanted if its
rewriters have unfilled coercion holes; see
Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint.
But if we thereby suppress *all* errors that's really confusing,
and as #22707 shows, GHC goes on without even realising that the
program is broken. Disaster.
This MR arranges to un-suppress them all if they all get suppressed.
Close #22707
- - - - -
5 changed files:
- compiler/GHC/Tc/Errors.hs
- compiler/GHC/Tc/Types/Constraint.hs
- + testsuite/tests/typecheck/should_fail/T22707.hs
- + testsuite/tests/typecheck/should_fail/T22707.stderr
- testsuite/tests/typecheck/should_fail/all.T
Changes:
=====================================
compiler/GHC/Tc/Errors.hs
=====================================
@@ -476,30 +476,37 @@ mkErrorItem ct
, ei_m_reason = m_reason
, ei_suppress = suppress }}
+-- | Actually report this 'ErrorItem'.
+unsuppressErrorItem :: ErrorItem -> ErrorItem
+unsuppressErrorItem ei = ei { ei_suppress = False }
+
----------------------------------------------------------------
reportWanteds :: SolverReportErrCtxt -> TcLevel -> WantedConstraints -> TcM ()
reportWanteds ctxt tc_lvl wc@(WC { wc_simple = simples, wc_impl = implics
, wc_errors = errs })
| isEmptyWC wc = traceTc "reportWanteds empty WC" empty
| otherwise
- = do { tidy_items <- mapMaybeM mkErrorItem tidy_cts
+ = do { tidy_items1 <- mapMaybeM mkErrorItem tidy_cts
; traceTc "reportWanteds 1" (vcat [ text "Simples =" <+> ppr simples
, text "Suppress =" <+> ppr (cec_suppress ctxt)
, text "tidy_cts =" <+> ppr tidy_cts
- , text "tidy_items =" <+> ppr tidy_items
+ , text "tidy_items1 =" <+> ppr tidy_items1
, text "tidy_errs =" <+> ppr tidy_errs ])
- -- This check makes sure that we aren't suppressing the only error that will
- -- actually stop compilation
- ; assertPprM
- ( do { errs_already <- ifErrsM (return True) (return False)
- ; return $
- errs_already || -- we already reported an error (perhaps from an outer implication)
- null simples || -- no errors to report here
- any ignoreConstraint simples || -- one error is ignorable (is reported elsewhere)
- not (all ei_suppress tidy_items) -- not all errors are suppressed
- } )
- (vcat [text "reportWanteds is suppressing all errors"])
+ -- Catch an awkward case in which /all/ errors are suppressed:
+ -- see Wrinkle at end of Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint
+ -- Unless we are sure that an error will be reported some other way (details
+ -- in the defn of tidy_items) un-suppress the lot. This makes sure we don't forget to
+ -- report an error at all, which is catastrophic: GHC proceeds to desguar and optimise
+ -- the program, even though it is full of type errors (#22702, #22793)
+ ; errs_already <- ifErrsM (return True) (return False)
+ ; let tidy_items
+ | not errs_already -- Have not already reported an error (perhaps
+ -- from an outer implication); see #21405
+ , not (any ignoreConstraint simples) -- No error is ignorable (is reported elsewhere)
+ , all ei_suppress tidy_items1 -- All errors are suppressed
+ = map unsuppressErrorItem tidy_items1
+ | otherwise = tidy_items1
-- First, deal with any out-of-scope errors:
; let (out_of_scope, other_holes, not_conc_errs) = partition_errors tidy_errs
=====================================
compiler/GHC/Tc/Types/Constraint.hs
=====================================
@@ -2127,10 +2127,10 @@ uses GHC.Tc.Utils.anyUnfilledCoercionHoles to look through any filled coercion
holes. The idea is that we wish to report the "root cause" -- the error that
rewrote all the others.
-Worry: It seems possible that *all* unsolved wanteds are rewritten by other
-unsolved wanteds, so that e.g. w1 has w2 in its rewriter set, and w2 has
-w1 in its rewiter set. We are unable to come up with an example of this in
-practice, however, and so we believe this case cannot happen.
+Wrinkle: In #22707, we have a case where all of the Wanteds have rewritten
+each other. In order to report /some/ error in this case, we simply report
+all the Wanteds. The user will get a perhaps-confusing error message, but
+they've written a confusing program!
Note [Avoiding rewriting cycles]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
=====================================
testsuite/tests/typecheck/should_fail/T22707.hs
=====================================
@@ -0,0 +1,22 @@
+module T22707 where
+
+newtype Cont o i a = Cont {runCont ::(a -> i) -> o }
+
+t1:: Cont (i2 -> o) i1 a -> Cont o i2 (a -> i1)
+t1 c = Cont $ \ati1tti2 -> (runCont c) (ati1tti2 $ \a -> evalCont (t1 c) >>== \ati1 -> return ati1 a )
+
+evalCont:: Cont o a a -> o
+evalCont c = (runCont c)id
+
+instance Monad (Cont p p) where
+ return a = Cont ($ a)
+ (>>=) = (>>==)
+
+class PMonad m where
+ (>>==):: m p q a -> (a -> m q r b) -> m p r b
+
+instance PMonad Cont where
+ (Cont cont) >>== afmb = Cont $ \bti -> cont $ \a -> (runCont . afmb) a bti
+
+main:: IO ()
+main = putStrLn "bug"
=====================================
testsuite/tests/typecheck/should_fail/T22707.stderr
=====================================
@@ -0,0 +1,16 @@
+
+T22707.hs:6:37: error: [GHC-18872]
+ • Couldn't match kind ‘*’ with ‘GHC.Types.RuntimeRep’
+ When matching types
+ p0 :: *
+ GHC.Types.LiftedRep :: GHC.Types.RuntimeRep
+ Expected: Cont o i1 a
+ Actual: Cont (i2 -> o) i1 a
+ • In the first argument of ‘runCont’, namely ‘c’
+ In the expression:
+ (runCont c)
+ (ati1tti2 $ \ a -> evalCont (t1 c) >>== \ ati1 -> return ati1 a)
+ In the second argument of ‘($)’, namely
+ ‘\ ati1tti2
+ -> (runCont c)
+ (ati1tti2 $ \ a -> evalCont (t1 c) >>== \ ati1 -> ...)’
=====================================
testsuite/tests/typecheck/should_fail/all.T
=====================================
@@ -321,6 +321,7 @@ test('T7856', normal, compile_fail, [''])
test('T7869', normal, compile_fail, [''])
test('T7892', normal, compile_fail, [''])
test('T7809', normal, compile_fail, [''])
+test('T22707', normal, compile_fail, [''])
test('T7989', normal, compile_fail, [''])
test('T8034', normal, compile_fail, [''])
test('T8142', normal, compile_fail, [''])
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/1ed573a53ee454db240b9fb1a17e28c97b6eb53a
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/1ed573a53ee454db240b9fb1a17e28c97b6eb53a
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