Missing instances if compiling with -fplugin

Using the example from "9.3.3.2. Using Annotations" of the GHC user manual does not work correctly with GHC 7.10. The following fails:

$ ghc -c Bug1.hs -fplugin=SayAnnNames.Plugin

Bug1.hs:5:1:
    No instance for (Data SomeAnn) arising from an annotation
    In the annotation: {-# ANN foo SomeAnn #-}

It does not seem to matter why the type class is required:

$ ghc -c Bug2.hs -fplugin=SayAnnNames.Plugin

Bug2.hs:10:7:
    No instance for (Data SomeAnn) arising from a use of ‘bar’
    In the expression: bar SomeAnn
    In an equation for ‘baz’: baz = bar SomeAnn

Compiling without -fplugin works fine, though. If SomeAnn is defined in a different module than SayAnnNames.Plugin and reexported from it, the instances are in scope, too.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import typechecker labels

Attached file ann-bug-0.1.0.0.tar.gz (download).

Cabal package containing the example plugin from the user manual

Attached file Bug1.hs ($1080).

Attached file Bug2.hs ($1081).

mentioned in issue #10420 (closed)

closed

Pretty sure this is a duplicate of #10420 (closed), which was reported later but has a proper diagnosis of the problem. But maybe we should put this test example into the test suite in any case.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate
BlockedBy	→ #10420 (closed)

mentioned in commit 0cb1f5cf

mentioned in commit 4ee658a0

mentioned in commit 8e6a5033

reopened

The pre_cmd of T10294 and T10294a generates the following warning with a devel2 build:

$ make -s --no-print-directory -C annotation-plugin package.T10294
WARNING: file compiler/specialise/Specialise.hs, line 722
  specImport discarding: mapM_ :: forall a_a5Mh
                                         (m_a5Mi :: * -> *)
                                         b_a5Mj
                                         (t_a5Mk :: * -> *).
                                  (Foldable t_a5Mk, Monad m_a5Mi) =>
                                  (a_a5Mh -> m_a5Mi b_a5Mj) -> t_a5Mk a_a5Mh -> m_a5Mi ()
    want: False
    stable: False
    calls: mapM_ _ @ CoreM _ @ [] $fFoldable[] $fMonadCoreM

This makes the test fail for me, even when DYNAMIC_GHC_PROGRAMS=YES (my timeout program stops working for some reason when it sees unexpected output). I don't know if the warning can be ignored, so I'm reopening this ticket.

Trac metadata

Trac field	Value
Resolution	ResolvedDuplicate → Unresolved
Test case	→ plugins/T10294, plugins/T10294a

closed

Nevermind, that warning only shows up when ghc is compiled with -DDEBUG, and is not related to this ticket at all. Closing as duplicate again.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

changed milestone to %8.0.1

Milestone renamed

mentioned in commit 0cad52d6

added Pnormal label