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Summary:
The validity check which rejected things like:

```lang=haskell
type family B x where
  A x = x
```

Used to live in the typechecker. But it turns out that this validity
check was //only// being run on closed type families without CUSKs!
This meant that GHC would silently accept something like this:

```lang=haskell
type family B (x :: *) :: * where
  A x = x
```

This patch fixes the issue by moving this validity check to the
renamer, where we can be sure that the check will //always// be run.

Test Plan: make test TEST=T16002

Reviewers: simonpj, bgamari

Reviewed By: simonpj

Subscribers: goldfire, rwbarton, carter

GHC Trac Issues: #16002

Differential Revision: https://phabricator.haskell.org/D5420

To check whether a given module has been imported, we do the following:
From the list of all qualified names we extract the distinct module
names to a list of module names.
Then we check whether the given module name is in this list of module
names.

Test Plan: make test TEST=T14225

Reviewers: mpickering, hvr, monoidal, osa1, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, carter

GHC Trac Issues: #14225

Differential Revision: https://phabricator.haskell.org/D5331

Summary:
Fix a bug in commit 12eeb9 which permits the following:

```
class C a where
  type T a b
instance C (Maybe a) where
  type forall a b. T (Maybe a) b = b
```

where instead, the user should write:

```
instance C (Maybe a) where
  type forall b. T (Maybe a) b = b
```

Update the users guide to discuss scoping of type variables in
explicit foralls in type family instances.

Test Plan: validate

Reviewers: bgamari, goldfire, monoidal

Reviewed By: goldfire

Subscribers: monoidal, rwbarton, carter

GHC Trac Issues: #15828

Differential Revision: https://phabricator.haskell.org/D5283

Summary:
For the error message:
    Not in scope X.Y
    Module X does not export Y
    No module named ‘X’ is imported:
there are 2 cases, where we don't show the last "no module named is imported" line:
1. If the module X has been imported.
2. If the module X is the current module. There are 2 subcases:

   2.1 If the unknown module name is in a input source file,
       then we can use the getModule function to get the current module name.

   2.2 If the unknown module name has been entered by the user in GHCi,
       then the getModule function returns something like "interactive:Ghci1",
       and we have to check the current module in the last added entry of
       the HomePackageTable.

Test Plan: make test TESTS="T15611a T15611b"

Reviewers: monoidal, hvr, thomie, dfeuer, bgamari, DavidEichmann

Reviewed By: monoidal, DavidEichmann

Subscribers: rwbarton, carter

GHC Trac Issues: #15611

Differential Revision: https://phabricator.haskell.org/D5284

Allow the user to explicitly bind type/kind variables in type and data
family instances (including associated instances), closed type family
equations, and RULES pragmas. Follows the specification of GHC
Proposal 0007, also fixes #2600. Advised by Richard Eisenberg.

This modifies the Template Haskell AST -- old code may break!

Other Changes:
- convert HsRule to a record
- make rnHsSigWcType more general
- add repMaybe to DsMeta

Includes submodule update for Haddock.

Test Plan: validate

Reviewers: goldfire, bgamari, alanz

Subscribers: simonpj, RyanGlScott, goldfire, rwbarton,
             thomie, mpickering, carter

GHC Trac Issues: #2600, #14268

Differential Revision: https://phabricator.haskell.org/D4894

Summary:
This means that 'GHC.Classes.(%,%)' is no longer mentioned in
error messages for things like

   class (a,b,c)  -- outside of 'GHC.Classes'
   class (a,Bool)

Test Plan: make TEST=T14907a && make TEST=T14907b

Reviewers: RyanGlScott, bgamari

Reviewed By: RyanGlScott

Subscribers: rwbarton, carter

GHC Trac Issues: #14907

Differential Revision: https://phabricator.haskell.org/D5172

This fixes Trac #15607. The general pattern is well
established (e.g. see the guard_op binding in rnStmt
of BodyStme), but we weren't using it for LastStmt.

Most out of scope errors get reported by the type checker these
days, but not all.  Example, the function on the LHS of a RULE.

Trace #15659 pointed out that this less-heavily-used code path
produce a "wacky" error message.  Indeed so.  Easily fixed.

Trac #15487 correctly reported that the qualification
of a Name in an ambiguous-occurrence error message was
wrong.  This patch fixes it.

It's easily done, in RnUtils.addNameClashErrRn

The problem was that in complaining about M.x we must
enusre that 'M' part is the same as that used in
pprNameProvenance.

In TcErrors, cec_suppress is used to suppress low-priority
errors in favour of truly insoluble ones.

But I was failing to initialise it correcly at top level, which
resulted in Trac #15539.  Easy to fix.

A few regression tests have fewer errors reported, but that seems to
be an improvement.

Two tests - a ghci script and a compile fail test have been added.

This changes an obscure error (which mistakenly mentions
Template Haskell) to one that makes more sense.

Test Plan: make test TEST=T15214

Reviewers: bgamari, mpickering

Reviewed By: bgamari, mpickering

Subscribers: mpickering, rwbarton, thomie, carter

GHC Trac Issues: #15214

Differential Revision: https://phabricator.haskell.org/D4768

This fixes Trac #14591

I took the opportunity to delete the dead code isMonadCompExpr

this is a remains from supporting Result Type Signaturs in the ancient
past.

Differential Revision: https://phabricator.haskell.org/D4066

When a record contruction or pattern uses a data constructor
that isn't in scope, we may produce spurious ambiguous-field
errors (Trac #14307).  E.g.

   f (A { fld = x }) = e

where 'A' is not in scope.  We want to draw attention to the
out-of-scope data constructor first; once that is fixed we
can think about the fields.

This patch suppresses the field errors if the data con is out
of scope.

Test Plan: new test for #13847, and the test for #13644 now passes

Reviewers: mpickering, austin, bgamari, simonpj

Reviewed By: mpickering, simonpj

Subscribers: simonpj, rwbarton, thomie

GHC Trac Issues: #13644, #13847

Differential Revision: https://phabricator.haskell.org/D3988

Commit 2484d4da accidentally dropped a
call to `isUnboundName` in an important location. This re-adds it.

Fixes #13947.

Test Plan: make test TEST=T13947

Reviewers: adamgundry, austin, bgamari

Reviewed By: adamgundry

Subscribers: rwbarton, thomie

GHC Trac Issues: #13947

Differential Revision: https://phabricator.haskell.org/D3718

Given multiple in-scope constructors with the same name, say `A`, and a
function of type `A -> Int`, say, the compiler reports both a "type `A`
is not in scope" and (incorrectly) an ambiguity error. The latter
shouldn't be there if `DataKinds` isn't enabled.

This issue was recommended to me by @mpickering as a suitable first
task, and the fix was also outlined in the original Trac ticket. It
involved a simple reordering of the steps taken in `lookup_demoted` in
`RnEnv.hs`. The fix is to make the `DataKinds` check happen earlier,
ensuring that the ambiguity check doesn't happen at all if we know the
constructors couldn't have been promoted.
Signed-off-by: Soham Chowdhury <chow.soham@gmail.com>

Reviewers: mpickering, austin, bgamari

Reviewed By: mpickering, bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #13568

Differential Revision: https://phabricator.haskell.org/D3547

The problem originates in TcPat.find_field_ty but I don't know how to
clearnly fix it.

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #13644

Differential Revision: https://phabricator.haskell.org/D3535

The script I used is included as testsuite/driver/kill_extra_files.py,
though at this point it is for mostly historical interest.

Some of the tests in libraries/hpc relied on extra_files.py, so this
commit includes an update to that submodule.

One test in libraries/process also relies on extra_files.py, but we
cannot update that submodule so easily, so for now we special-case it
in the test driver.

The `clean_cmd` and `extra_clean` setup functions don't do anything.
Remove them from .T files.

Created using https://github.com/thomie/refactor-ghc-testsuite. This
diff is a test for the .T-file parser/processor/pretty-printer in that
repository.

    find . -name '*.T' -exec ~/refactor-ghc-testsuite/Main "{}" \;

Tests containing inline comments or multiline strings are not modified.

Preparation for #12223.

Test Plan: Harbormaster

Reviewers: austin, hvr, simonmar, mpickering, bgamari

Reviewed By: mpickering

Subscribers: mpickering

Differential Revision: https://phabricator.haskell.org/D3000

GHC Trac Issues: #12223

This fixes #11592.

Test Plan: validate

Reviewers: simonpj, austin, bgamari, goldfire

Reviewed By: goldfire

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2914

GHC Trac Issues: #11592

Previously when encountering EAsPat in an expression context,
TypeApplications was suggested even when already enabled. This patch
replaces the suggestion with more appropriate message.

Test Plan: validate

Reviewers: austin, bgamari, mpickering, goldfire, simonpj

Reviewed By: mpickering, goldfire, simonpj

Subscribers: simonpj, goldfire, mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D2877

GHC Trac Issues: #12879

Trac #12686 showed that we were allowing a term variable into
a type, by promotion.  I chose to squash this in the renamer.

This fixes #12584, where wildcard patterns were snuck into an
expression, which then crashed the typechecker in TcExpr since EWildPats
aren't supposed to appear in the AST after renaming.

The problem was that `rnTopSpliceDecl` failed to check for errors from
`rnSplice` (as done by other callers to `rnSplice`).

Thanks to Shayan for reporting this!

Reviewers: simonpj, austin

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D2539

GHC Trac Issues: #12584

Now the message explains why closed variables are not closed when
encountered in the body of (static ...).

This required adding to the local environment the free variables of
the local bindings in scope. Thus we can analyze and explain why a
variable is not closed when encountered.

Test Plan: ./validate

Reviewers: austin, simonpj, bgamari

Reviewed By: bgamari

Subscribers: mboes, thomie

Differential Revision: https://phabricator.haskell.org/D2167

GHC Trac Issues: #12003

This should require -XScopedTypeVariables. It seems this was previously
handled by RnTypes.rnHsBndrSig which called RnTypes.badKindSigErr but
this was broken in Simon's refactor of wildcards,
1e041b73. Here we re-introduce a check
in RnPat. See #11663.

Test Plan: Validate with `T11663`

Reviewers: austin, simonpj

Reviewed By: austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2054

GHC Trac Issues: #11663

Since we're not consisently keeping track of which tests should pass
with which compiler versions, there is no point in keeping these
functions.

Update submodules containers, hpc and stm.

Now for unqualified imports. Improves upon #11071.

Unfortunately, it seems that since 7.10, ghc will not print all
out-of-scope errors.

Test Plan: test suite updated

Reviewers: austin, thomie, bgamari

Reviewed By: bgamari

Differential Revision: https://phabricator.haskell.org/D1478

GHC Trac Issues: #11071

This implements #11071. It needs to thread through a GlobalRdrEnv
corresponding to the export list of the module if its exports were not
restricted.

A refactoring of ImportedModsVal into a proper data type follows.

Differential Revision: https://phabricator.haskell.org/D1462

For details see #6018, Phab:D202 and the wiki page:

https://ghc.haskell.org/trac/ghc/wiki/InjectiveTypeFamilies

This patch also wires-in Maybe data type and updates haddock submodule.

Test Plan: ./validate

Reviewers: simonpj, goldfire, austin, bgamari

Subscribers: mpickering, bgamari, alanz, thomie, goldfire, simonmar,
             carter

Differential Revision: https://phabricator.haskell.org/D202

GHC Trac Issues: #6018

Test names should be unique. This fixes a framework failure.

The provoking cause for this patch is Trac #5001, comment:23.  There
was an INLINE pragma in an instance decl, that shouldn't be there.
But there was no complaint, just a  mysterious WARN later.

I ended up having to do some real refactoring but the result is,
I think, simpler and more robust.

When a constructor was mistakenly imported directly instead of as a
constructor of a data type, a hint will be shown on how to correctly
import
it. Just like the constructor, the data type should be surrounded in
parentheses if it is an operator (TypeOperator in this case).

Instead of:

    error:
        In module ‘Data.Type.Equality’:
          ‘Refl’ is a data constructor of ‘:~:’
        To import it use
          ‘import’ Data.Type.Equality( :~:( Refl ) )
        or
          ‘import’ Data.Type.Equality( :~:(..) )

Print:

    error:
        In module ‘Data.Type.Equality’:
          ‘Refl’ is a data constructor of ‘(:~:)’
        To import it use
          ‘import’ Data.Type.Equality( (:~:)( Refl ) )
        or
          ‘import’ Data.Type.Equality( (:~:)(..) )

Test Plan: pass new test

Reviewers: austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1093

GHC Trac Issues: #10668

Out of scope variables now generate HsUnboundVar,
and the fixity re-jigging wasn't taking this into
account.