#8740: Deriving instance conditionally compiles
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Reporter: thomaseding | Owner: (none)
Type: bug | Status: closed
Priority: normal | Milestone: 8.6.1
Component: Compiler (Type | Version: 7.6.3
checker) | Keywords: GADTs,
Resolution: fixed | deriving
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: GHC rejects | Test Case:
valid program | deriving/should_compile/T8740
Blocked By: | Blocking:
Related Tickets: #8128, #11066 | Differential Rev(s):
Wiki Page: |
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Comment (by Krzysztof Gogolewski ):
In [changeset:"44a7b9baa45c4ab939c7d996519b5e3de3e13c5a/ghc" 44a7b9b/ghc]:
{{{
#!CommitTicketReference repository="ghc"
revision="44a7b9baa45c4ab939c7d996519b5e3de3e13c5a"
Suppress -Winaccessible-code in derived code
Summary:
It's rather unfortunate that derived code can produce inaccessible
code warnings (as demonstrated in #8128, #8740, and #15398), since
the programmer has no control over the generated code. This patch
aims to suppress `-Winaccessible-code` in all derived code. It
accomplishes this by doing the following:
* Generalize the `ic_env :: TcLclEnv` field of `Implication` to
be of type `Env TcGblEnc TcLclEnv` instead. This way, it also
captures `DynFlags`, which record the flag state at the time
the `Implication` was created.
* When typechecking derived code, turn off `-Winaccessible-code`.
This way, any insoluble given `Implication`s that are created when
typechecking this derived code will remember that
`-Winaccessible-code` was disabled.
* During error reporting, consult the `DynFlags` of an
`Implication` before making the decision to report an inaccessible
code warning.
Test Plan: make test TEST="T8128 T8740 T15398"
Reviewers: simonpj, bgamari
Reviewed By: simonpj
Subscribers: monoidal, rwbarton, thomie, carter
GHC Trac Issues: #8128, #8740, #15398
Differential Revision: https://phabricator.haskell.org/D4993
}}}
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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8740#comment:9
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