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TcErrors has a system for suppressing some type errors if a more
serious one occurs.  But there was a crucial missing case, which
sometimes resulted in a cascade of irrelevant errors overwhelming
the actual cause. This was Trac #11541.

The fix is simple.  Worth merging to 8.0

When renaming a HsVar it can be converted to a HsRecField. In the
process the location of the enclosed name is converted to a noLoc

Closes #11576

be3d7f66

 added Show
instance for Callstack.

That made a couple of error messages to drift as:

             instance Show Ordering -- Defined in ‘GHC.Show’
             instance Show Integer -- Defined in ‘GHC.Show’
             ...plus 23 others
    -        ...plus 20 instances involving out-of-scope types
    +        ...plus 21 instances involving out-of-scope types
Signed-off-by: Sergei Trofimovich <siarheit@google.com>

- Document that you can use 'forall' in instance decls

- Change the sections a bit, so that big sections (like
  lexically scoped type variables, pattern synonyms,
  implicit parameters) become more visible

No change in behaviour

Reduces un-neede parens.

Also -fprint-typechecker-elaboration now makes type applications
and casts in expressions also appear.  (Previously those were
confusingly controlled by -fprint-explicit-coercions.)

Makes it a slightly more stringent test of record pattern bindings

In poking Trac #11414 I found myself sinking into the abe_inst_wrap
swamp.  What is this strange thing?  (It turned out that #11414 was
breaking because of it.)

Thrillingly, I found a way to sweep it away again, putting the deep
instantation into tcMonoBinds instead of mkExport; and it turned out
that the fun_co_fn field of FunBind was already there ready to receive
exactly this wrapper. Hooray.  Result

* Death to abe_inst_wrap
* Death to mbi_orig
* Death to the plumbing in tcPolyInfer that did the
  deep instantiation

I did find that I had to re-engineer the treatment of instance type
signatures (again), but the result looks more modular and robust to
me.

And #11414 is fixed.

This reverts commit dbf72dbc.
This commit introduced performance regressions:
https://ghc.haskell.org/trac/ghc/ticket/11371#comment:27,
I will push it again after I fix it.

Test Plan: revert

Reviewers: simonpj, bgamari, simonmar, austin, goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D1907

Summary:
Ties up loose ends from D1894.

GHC 7.10.2 and 7.10.3 featured a `Show` instance for `CallStack`, but since it
was derived, it broke encapsulation. This adds a `Show` instance which displays
the `CallStack` as if it were a `[(String, SrcLoc)]`.

To ensure that the output of `Show` is technically a valid Haskell term, we
also add a corresponding `IsList CallStack` instance.

Reviewers: gridaphobe, austin, hvr, bgamari

Reviewed By: gridaphobe, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1903

This reverts commit 51a33924.

This fixes a bug where piResultTy created
substitutions that would violate both of the invariants
in Note [The substitution invariant].

Test Plan: ./validate --slow

Reviewers: goldfire, simonpj, austin, bgamari

Reviewed By: simonpj, bgamari

Subscribers: simonmar, thomie

Differential Revision: https://phabricator.haskell.org/D1855

GHC Trac Issues: #11371

nkartashov authored Feb 11, 2016 and Ben Gamari committed Feb 11, 2016

Previously, all flags were present in user suggest and completion. This commit
removes the deprecated ones from there. It is done by saving deprecation info
at the moment of flag definition.

Reviewers: rwbarton, austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D1883

There were two bugs here:

* We weren't ignoring Cast in size_up_app
* An application of a non-variable wasn't being charged correct

The result was that some things looked too cheap.  In my case I had
things like

    ((f x) `cast` ...) y

which was given size 21 instead of 30, and this had knock-on effects
elsewhere that caused some large code bloat.

Test Plan:
* nofib runs (todo)
* validate

Reviewers: simonpj, austin, bgamari, erikd

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1900

GHC Trac Issues: #11564

...following a question from Conal

See Note [Eta-reduction in -O0] in DynFlags.

Bottom line: doing eta reduction unconditionally is benign, and
removes an ASSERT failure (Trac #11562).

It's just a small cleanup. There should be no change in
behaviour.

Test Plan: ./validate --slow

Reviewers: austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: thomie, simonmar

Differential Revision: https://phabricator.haskell.org/D1901

This simple change fixes Trac #11563, #11520, #11516, #11399.
See esp the comments in #11520.

See Note [Fail fast on kind errors] in TcSimplify

Merge to 8.0 branch

Noticed as a sphinx warning:
    docs/users_guide/flags-warnings.gen.rst:97:
        WARNING: Inline interpreted text or phrase
        reference start-string without end-string.

Which pointed to broken table.

Before the patch table looked like:

    | :ghc-flag:`-Wno-unticked-promoted-constructors |
    | `                                              |

After the patch long link is on a single line:

    | :ghc-flag:`-Wno-unticked-promoted-constructors`    |
Signed-off-by: Sergei Trofimovich <siarheit@google.com>

Noticed when looked through sphinx warnings:
    docs/users_guide/safe_haskell.rst:4:
        SEVERE: Duplicate ID: "ghc-flag-Issue"
Signed-off-by: Sergei Trofimovich <siarheit@google.com>

Edward Z. Yang authored Feb 10, 2016 and Ben Gamari committed Feb 10, 2016

On the GHC 8.0 RCs, multiple users reported a very strange error
whereby GHC would complain that the symbols names recorded in interface
files did not match the expected name.  The reason for this is
that they were using an old version of Cabal which chose symbol
names differently from the installed package ID ('id' field) which
the package was to be installed with; GHC 8.0 now mandates that
these coincides.

This change adds a test to ghc-pkg to make sure that 'id' and 'key'
(which is how Cabal previously reported what the symbol name
was supposed to be) match; if they don't match or key is missing,
we assume that the Cabal was too old.

Bikeshed points:

    - Should we offer more information about how to upgrade
      Cabal correctly (i.e. specify a version?)

    - Should we allow for a missing 'key'?  If we allow for
      'key' to be missing, we lose the ability to detect
      Cabal from GHC 7.8 or earlier being used.  If we
      require it to be specified, then it will not be possible
      for Cabal to deprecate the (unused) field and remove it
      without having BC for 8.0.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: austin, bgamari, hvr

Reviewed By: hvr

Subscribers: bergmark, thomie

Differential Revision: https://phabricator.haskell.org/D1892

GHC Trac Issues: #11558

owst authored Feb 10, 2016 and Ben Gamari committed Feb 10, 2016

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1899

bollmann authored Feb 10, 2016 and Ben Gamari committed Feb 10, 2016

The bug itself has already been fixed in #10734, so this
only adds another regression test (as given in the ticket).

Test Plan: ./validate

Reviewers: goldfire, austin, thomie, bgamari

Reviewed By: bgamari

Differential Revision: https://phabricator.haskell.org/D1898

GHC Trac Issues: #9022

GHC does not use passed paramaters anywhere
for this deprecated option.
Signed-off-by: Sergei Trofimovich <siarheit@google.com>

Previously "types" was inappropriately made plural instead of
"instance",

    instance Eq Ordering -- Defined in ‘GHC.Classes’
    ...plus 24 others
    ...plus 13 instance involving out-of-scope typess

Ryan Scott authored Feb 09, 2016 and Ben Gamari committed Feb 09, 2016

GHC 7.10.2 and 7.10.3 had a derived `Eq` instance for `SrcLoc`, but it
seems to have been removed (see
6740d70d) during GHC 8.0 development.

Reviewers: hvr, austin, gridaphobe, bgamari

Reviewed By: gridaphobe, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1894

Ben Gamari authored Feb 09, 2016 and Ben Gamari committed Feb 09, 2016

Test Plan: GREP_OPTIONS=--blah ./validate

Reviewers: austin, thomie

Reviewed By: thomie

Differential Revision: https://phabricator.haskell.org/D1887

GHC Trac Issues: #11530

Thomas Miedema authored Feb 09, 2016 and Ben Gamari committed Feb 09, 2016

When CrossCompiling=YES or Stage1Only=YES, building the haddocks and the
User's Guide should be skipped, because haddock and mkUserGuidePart
depend on the GHC API.
See Note [No stage2 packages when CrossCompiling or Stage1Only] for
details.

There are several places in the build system where the variables
HADDOCK_DOCS and BUILD_SPHINX_* are checked. Instead of also checking
for the variables CrossCompiling or Stage1Only in all those places,
`make` will now exit with a nice error message when the user requests
the impossible.

Reviewers: rwbarton, austin, bgamari

Reviewed By: bgamari

Differential Revision: https://phabricator.haskell.org/D1882

Jonas Scholl authored Feb 09, 2016 and Ben Gamari committed Feb 09, 2016

The module CmmLayoutStack removes stack checks if a function does not
use stack space. However, it can only recognize checks of the form
Sp < SpLim. However, these checks get sometimes rewritten to
Sp >= SpLim (with both branches swapped), so we better recognize these
checks too.

Test Plan: ./validate

Reviewers: austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1881

GHC Trac Issues: #11533

This was largely fixed by the re-rework of the pattern match checker.
Resolves #5642.

Ben Gamari authored Feb 08, 2016 and Ben Gamari committed Feb 09, 2016

Reviewers: austin, thomie

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1893

We also need to update `stgBindHasCafRefs` assertion with this change,
as we no longer have the pre-computed SRT, LiveVars etc. We rename it to
`topStgBindHasCafRefs` and implement it like this:

A non-updatable top-level binding may refer to a CAF by referring to a
top-level definition with CAFs. A top-level definition may have CAFs if
it's updatable. At this point (because this is done after TidyPgm)
top-level Ids (whether imported or defined in this module) are
GlobalIds, so the top-levelness test is easy. (see also comments in the
code)

Reviewers: bgamari, simonpj, austin

Reviewed By: simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1889

GHC Trac Issues: #11550

tyConRolesRepresentational is just a version of tyConRolesX, but
specialised for a Representational argument. Saves a bit of extra
argument passing and pattern matching, and tyConRolesX was often
called when we knew the argument role was Representational.

Rather to my surprise this made the compiler allocate 5% less
for tests T9872{b,c,d}.  At least I think it's this commit.
Good thing, regardless.