GitLab

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Summary:
Previously, GHC would look for instances of wired-in packages in the
in-memory package database and null out the version number.  This was
necessary when the sourcePackageId was used to determine the linker
symbols; however, we now use a package key, so only that needs to be
updated.

Long-term, we can remove this hack by ensuring that Cabal actually records
the proper package key in the database.  This will also fix an unrelated
hack elsewhere.

Keeping version numbers means that wired in packages get rendered differently
when output by GHC.  This is the source of all the test-case output changes.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: hvr, austin

Subscribers: simonmar, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D170

* Deprecate -XOverlappingInstances

* Update test suite.  Several tests even had entirely unnecessary
  uses of -XOverlappingInstances

* Update user manual with a careful description of the instance
  resolution story

* Fix an outright bug in the handling of duplidate instances in GHCi,
  which are meant to silently overwrite the earlier duplicate. The
  logic was right for family instances but was both more complicated,
  and plain wrong, for class instances.  (If you are interested, the
  bug was that we were eliminating the duplicate from the InstEnv, but
  not from the [ClsInst] held in tcg_insts.)  Test is ghci044a.

All the initial work on this was done fy 'archblob' (fcsernik@gmail.com);
thank you!

I reviewed the patch, started some tidying, up and then ended up in a huge
swamp of changes, not all of which I can remember now.  But:

* To suppress kind arguments when we have -fno-print-explicit-kinds,
    - IfaceTyConApp argument types are in a tagged list IfaceTcArgs

* To allow overloaded types to be printed with =>, add IfaceDFunTy to IfaceType.

* When printing data/type family instances for the user, I've made them
  print out an informative RHS, which is a new feature. Thus
        ghci> info T
        data family T a
        data instance T Int = T1 Int Int
        data instance T Bool = T2

* In implementation terms, pprIfaceDecl has just one "context" argument,
  of type IfaceSyn.ShowSub, which says
       - How to print the binders of the decl
         see note [Printing IfaceDecl binders] in IfaceSyn
       - Which sub-comoponents (eg constructors) to print

* Moved FastStringEnv from RnEnv to OccName

It all took a ridiculously long time to do.  But it's done!

We now do role inference on stupid datatype contexts, allowing a
lightweight role annotation syntax.