ASSERTion at TcMType:809 fails on test polykinds/T6068
On a recent run through the testsuite on a debug build, testcase polykinds/T6068 was triggering an assertion failure on line 809 of TcMType, which reads
ASSERT2( isWantedCt orig_ct, ppr orig_ct )in try_zonk_fun_eq in zonkFlats (just in case line numbers wibble a bit).
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.7 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |
Activity
mentioned in issue #8129 (closed)
mentioned in issue #8262 (closed)
added Tbug Trac import labels
I've tracked this down a bit (see comments to #8129 (closed)). The problem seems to have been introduced in e365d496. I don't know enough about the constraint solver to be sure of the right fix, however.
Trac metadata
Trac field Value Related → #8129 (closed) CC → adam.gundry@strath.ac.uk The comments should say #8314 (closed) not #8134 (closed).
In [changeset:8cfbdccb/ghc]: `repository="ghc" revision="8cfbdccb" Accommodate Derived constraints in two places (fix Trac #8129 (closed), #8134 (closed))
If we have class (F a ~ b) => C a b then we can produce derived CFunEqCans. These were not being treated properly in two places:
a) in TcMType.zonkFlats (Trac #8134 (closed)) b) in TcSMonad.prepareInertsForImplications (Trac #8129 (closed))
This patch fixes both. `
added Pnormal label
