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Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Haskell2010 implies (at least) EmptyDataDecls, ForeignFunctionInterface,
PatternGuards, DoAndIfThenElse, and RelaxedPolyRec.

This is a follow-up to dd92e217

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

This is a first step towards eliminating `default-extensions` in favour of
per-file declared `{-# LANGUAGE ... #-}` pragmas.
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

This corresponds to the RC of the soon-to-be Cabal 1.20 release

One noteworthy change is the removal of the `--with-ranlib` flag
requiring a small adaptation in the GHC build system.

Moreover two new licences were added, MPL and BSD2.

Due to https://github.com/haskell/cabal/issues/1622

 Cabal-1.20 now
allows to strip libraries as well, this doesn't work well with
`ghc-cabal copy` being fed a `":"` strip-command argument which was
simply ignored in the past. The current code tries to retain this
semantics as backward compat. However, this needs more investigation as
I'm not sure if/why the `test_bindist` step doesn't want the libraries
to be stripped on installation.
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

This patch implements Pattern Synonyms (enabled by -XPatternSynonyms),
allowing y ou to assign names to a pattern and abstract over it.

The rundown is this:

  * Named patterns are introduced by the new 'pattern' keyword, and can
    be either *unidirectional* or *bidirectional*. A unidirectional
    pattern is, in the simplest sense, simply an 'alias' for a pattern,
    where the LHS may mention variables to occur in the RHS. A
    bidirectional pattern synonym occurs when a pattern may also be used
    in expression context.

  * Unidirectional patterns are declared like thus:

        pattern P x <- x:_

    The synonym 'P' may only occur in a pattern context:

        foo :: [Int] -> Maybe Int
        foo (P x) = Just x
        foo _     = Nothing

  * Bidirectional patterns are declared like thus:

        pattern P x y = [x, y]

    Here, P may not only occur as a pattern, but also as an expression
    when given values for 'x' and 'y', i.e.

        bar :: Int -> [Int]
        bar x = P x 10

  * Patterns can't yet have their own type signatures; signatures are inferred.

  * Pattern synonyms may not be recursive, c.f. type synonyms.

  * Pattern synonyms are also exported/imported using the 'pattern'
    keyword in an import/export decl, i.e.

        module Foo (pattern Bar) where ...

    Note that pattern synonyms share the namespace of constructors, so
    this disambiguation is required as a there may also be a 'Bar'
    type in scope as well as the 'Bar' pattern.

  * The semantics of a pattern synonym differ slightly from a typical
    pattern: when using a synonym, the pattern itself is matched,
    followed by all the arguments. This means that the strictness
    differs slightly:

        pattern P x y <- [x, y]

        f (P True True) = True
        f _             = False

        g [True, True] = True
        g _            = False

    In the example, while `g (False:undefined)` evaluates to False,
    `f (False:undefined)` results in undefined as both `x` and `y`
    arguments are matched to `True`.

For more information, see the wiki:

    https://ghc.haskell.org/trac/ghc/wiki/PatternSynonyms
    https://ghc.haskell.org/trac/ghc/wiki/PatternSynonyms/Implementation

Reviewed-by: Simon Peyton Jones <simonpj@microsoft.com>
Signed-off-by: Austin Seipp <austin@well-typed.com>

This fixes bugs #8185, #8234, and #8246. The new syntax is explained
in the comments to #8185, appears in the "Roles" subsection of the
manual, and on the [wiki:Roles] wiki page.

This change also removes the ability for a role annotation on type
synonyms, as noted in #8234.

We now define _PROGNAME, and _PROG is automatically defined with
$(exeext). This will shortly automatically use the right exeext
depending on what stage it is being compiled with (exeext may be
different for different stages when cross-compiling).

This required various build system changes to get the build to go
through.

In the inplace shell wrappers, we set LD_LIBRARY_PATH to allow programs
to find their libraries. In the future, we might change the inplace tree
to be the same shape as an installed tree instead. However, this would
mean changing the way we do installation, as currently we use cabal's
installation methods to install the libraries, but that only works if
the libraries are under libraries/foo/dist-install/build/..., rather
than in inplace/lib/...

A side-effect is that we can no longer use the LogAction in
defaultErrorHandler, as we don't have DynFlags at that point.
But all that defaultErrorHandler did is to print Strings as
SevFatal, so now it takes a 'FatalMessager' instead.

stdout/stderr might be closed, so we can't just hFlush them.
So we instead allow configuration in the same way that log_action
is configurable.

This continues the clean up of the front end.  Since they
were first invented, type and data family *instance* decls
have been in the TyClDecl data type, even though they always
treated separately.

This patch takes a step in the right direction
  * The InstDecl type now includes both class instances and
    type/data family instances

  * The hs_tyclds field of HsGroup now never has any family
    instance declarations in it

However a family instance is still a TyClDecl.  It should really
be a separate type, but that's the next step.

All this was provoked by fixing Trac #5792 in the HEAD.
(I did a less invasive fix on the branch.)

You can now use type functions in FFI types.

Newtypes are now only looked through if the constructor is in scope.

It used to take a whole DynFlags, but that meant we had to
create a DynFlags with (panic "No settings") for settings, as
we didn't have any real settings.

Now we just pass the LogAction, which is all that it actually needed.
The default is exported from DynFlags as defaultLogAction.

makes it easier to remove everything built with stage1 in cases where
the build system or GHC wrongly thinks everything is up to date.

They belonged to the old generic deriving mechanism, so they can go. Adapted a lot of code as a consequence.

Stops us having to temporarily have a panic in the DynFlags.
We still need a panic in the DynFlags used for the top-level
error handler, though.

This patch fixes Trac #4875.  The main point is to do dependency
analysis on type and class declarations, and kind-check them in
dependency order, so as to improve error messages.

This patch means that a few programs that would typecheck before won't
typecheck any more; but before we were (naughtily) going beyond
Haskell 98 without any language-extension flags, and Trac #4875
convinces me that doing so is a Bad Idea.

Here's an example that won't typecheck any more
       data T a b = MkT (a b)
       type F k = T k Maybe

If you look at T on its own you'd default 'a' to kind *->*;
and then kind-checking would fail on F.

But GHC currently accepts this program beause it looks at
the *occurrences* of T.

This patch moves various functions that extract the binders
from a HsTyClDecl, HsForeignDecl etc into HsUtils, and gives
them consistent names.

By giving the dist-directory to ghctags we can get all the GHC API
flags we need in order to load the required modules.  The flag name
could perhaps be improved, but apart from that it seems to work well.

 - take the GHC topdir as a runtime argument
 - deal with files one at a time (fix space leak)