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Previously, GHC would not warn whenever there was a class instance that
didn't implement a class method whose name begins with an underscore.

Fixes #12959.

Test Plan: make test TEST=WarnMinimal

Reviewers: austin, bgamari, simonpj

Reviewed By: bgamari, simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2849

GHC Trac Issues: #12959

This patch reverts the change introduced with
587dcccf and restores the previous
default output of GHC (i.e., show source path and object path for each
compiled module).

The -fhide-source-paths flag can be used to hide these paths and reduce
the line
noise.

Reviewers: gracjan, nomeata, austin, bgamari, simonmar, hvr

Reviewed By: hvr

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2728

GHC Trac Issues: #12851

This patch add new options `-Werror=...`, `-Wwarn=...` and
`-Wno-error=...` (synonym for `-Wwarn=...`).

Semantics:

  - `-Werror` marks all warnings as fatal, including those that don't
    have a warning flag, and CPP warnings.
  - `-Werror=...` enables a warning and marks it as fatal
  - `-Wwarn=...` marks a warning as non-fatal, but doesn't disable it

Test Plan: validate

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: mpickering, svenpanne, RyanGlScott, thomie

Differential Revision: https://phabricator.haskell.org/D2706

GHC Trac Issues: #11219

Reviewers: simonmar, mpickering, austin, bgamari

Reviewed By: bgamari

Subscribers: mpickering, nomeata, thomie

Differential Revision: https://phabricator.haskell.org/D2679

GHC Trac Issues: #12807

This patch does a raft of useful tidy-ups in the type checker.
I've been meaning to do this for some time, and finally made
time to do it en route to ICFP.

1. Modify TcType.ExpType to make a distinct data type,
   InferResult for the Infer case, and consequential
   refactoring.

2. Define a new function TcUnify.fillInferResult, to fill in
   an InferResult. It uses TcMType.promoteTcType to promote
   the type to the level of the InferResult.
   See TcMType Note [Promoting a type]
   This refactoring is in preparation for an improvement
   to typechecking pattern bindings, coming next.

   I flirted with an elaborate scheme to give better
   higher rank inference, but it was just too complicated.
   See TcMType Note [Promotion and higher rank types]

3. Add to InferResult a new field ir_inst :: Bool to say
   whether or not the type used to fill in the
   InferResult should be deeply instantiated.  See
   TcUnify Note [Deep instantiation of InferResult].

4. Add a TcLevel to SkolemTvs. This will be useful generally

    - it's a fast way to see if the type
      variable escapes when floating (not used yet)

    - it provides a good consistency check when updating a
      unification variable (TcMType.writeMetaTyVarRef, the
      level_check_ok check)

   I originally had another reason (related to the flirting
   in (2), but I left it in because it seems like a step in
   the right direction.

5. Reduce and simplify the plethora of uExpType,
   tcSubType and related functions in TcUnify.  It was
   such an opaque mess and it's still not great, but it's
   better.

6. Simplify the uo_expected field of TypeEqOrigin.  Richard
   had generatlised it to a ExpType, but it was almost always
   a Check type.  Now it's back to being a plain TcType which
   is much, much easier.

7. Improve error messages by refraining from skolemisation when
   it's clear that there's an error: see
   TcUnify Note [Don't skolemise unnecessarily]

8. Type.isPiTy and isForAllTy seem to be missing a coreView check,
   so I added it

9. Kill off tcs_used_tcvs.  Its purpose is to track the
   givens used by wanted constraints.  For dictionaries etc
   we do that via the free vars of the /bindings/ in the
   implication constraint ic_binds.  But for coercions we
   just do update-in-place in the type, rather than
   generating a binding.  So we need something analogous to
   bindings, to track what coercions we have added.

   That was the purpose of tcs_used_tcvs.  But it only
   worked for a /single/ iteration, whereas we may have
   multiple iterations of solving an implication.  Look
   at (the old) 'setImplicationStatus'.  If the constraint
   is unsolved, it just drops the used_tvs on the floor.
   If it becomes solved next time round, we'll pick up
   coercions used in that round, but ignore ones used in
   the first round.

   There was an outright bug.  Result = (potentialy) bogus
   unused-constraint errors.  Constructing a case where this
   actually happens seems quite trick so I did not do so.

   Solution: expand EvBindsVar to include the (free vars of
   the) coercions, so that the coercions are tracked in
   essentially the same way as the bindings.

   This turned out to be much simpler.  Less code, more
   correct.

10. Make the ic_binds field in an implication have type
      ic_binds :: EvBindsVar
    instead of (as previously)
       ic_binds :: Maybe EvBindsVar
    This is notably simpler, and faster to use -- less
    testing of the Maybe.  But in the occaional situation
    where we don't have anywhere to put the bindings, the
    belt-and-braces error check is lost.  So I put it back
    as an ASSERT in 'setImplicationStatus' (see the use of
    'termEvidenceAllowed')

All these changes led to quite bit of error message wibbling

When looking up flags, we make sure to lookup the non-deprecated flags first
by ordering the list of flags.

Reviewers: bgamari, austin, mpickering

Reviewed By: mpickering

Subscribers: mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D2541

GHC Trac Issues: #12574

This fixes Trac #12597: in RnNames.warnMissingSignatures,
use pprSigmaType not pprType

Removes -Wredundant-constraints from -Wall, as per the
discussion in #10635.

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2498

GHC Trac Issues: #10635

This allows the removal of the override_flags stuff in testlib.py.

Summary:
foldUFM introduces unnecessary non-determinism that actually
leads to different generated code as explained in
Note [TrieMap determinism].

As we're switching from UniqFM to UniqDFM here you might be
concerned about performance. There's nothing that ./validate
detects. nofib reports no change in Compile Allocations, but
Compile Time got better on some tests and worse on some,
yielding this summary:

        -1 s.d.                -----            -3.8%
        +1 s.d.                -----            +5.4%
        Average                -----            +0.7%

This is not a fair comparison as the order of Uniques
changes what GHC is actually doing. One benefit from making
this deterministic is also that it will make the
performance results more stable.

Full nofib results: P108

Test Plan: ./validate, nofib

Reviewers: goldfire, simonpj, simonmar, austin, bgamari

Reviewed By: simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2169

GHC Trac Issues: #4012

Test Plan: It works, I promise.

Reviewers: austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1956

GHC Trac Issues: #11370

This was missed in bb5afd3c

This is extends bb5afd3c to cover
warnings emitted during lexing.

This implements another part of #10752

Both gcc and clang tell which warning flag a reported warning can be
controlled with, this patch makes ghc do the same. More generally, this
allows for annotated compiler output, where an optional annotation is
displayed in brackets after the severity.

This also adds a new flag `-f(no-)show-warning-groups` to control
whether to show which warning-group (such as `-Wall` or `-Wcompat`)
a warning belongs to. This flag is on by default.

This implements #10752

Reviewed By: quchen, bgamari, hvr

Differential Revision: https://phabricator.haskell.org/D1943

- Replace "Sigs" with "Signatures" in WarningFlag data constructors.
- Replace "PatSyn" with "PatternSynonym" in WarningFlag data
  constructors.
- Deprecate "missing-local-sigs" in favor of "missing-local-signatures".
- Deprecate "missing-exported-sigs" in favor of
  "missing-exported-signatures".
- Deprecate "missing-pat-syn-signatures" in favor of
  "missing-pattern-synonym-signatures".
- Replace "ddump-strsigs" with "ddump-str-signatures"

These complete the tasks that were explicitly mentioned in #11583

Test Plan:
Executed `ghc --show-options` and verified that the flags were changed
as expected.

Reviewers: svenpanne, austin, bgamari

Reviewed By: austin, bgamari

Subscribers: mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D1939

GHC Trac Issues: #11583

The MonadFail proposal implemented so far via #10751 only warns about
missing `MonadFail` instances based on existence of failible pattern
matches in `do`-blocks.

However, based on the noncanonical Monad warnings implemented via #11150
we can provide a different mechanism for detecting missing `MonadFail`
instances quite cheaply. That is, by checking for canonical `fail` definitions.

In the case of `Monad`/`MonadFail`, we define the canonical implementation of
`fail` to be such that the soft-deprecated method shall (iff overridden) be
defined in terms of the non-deprecated method. Consequently, in case of
`MonadFail`, the `Monad(fail)` method shall be defined as alias of
the `MonadFail(fail)` method.

This allows us at some distant point in the future to remove `fail` from
the `Monad` class, while having GHC ignore/tolerate such literal canonical
method definitions.

Reviewed By: bgamari, RyanGlScott

Differential Revision: https://phabricator.haskell.org/D1838

This re-working of the typechecker algorithm is based on
the paper "Visible type application", by Richard Eisenberg,
Stephanie Weirich, and Hamidhasan Ahmed, to be published at
ESOP'16.

This patch introduces -XTypeApplications, which allows users
to say, for example `id @Int`, which has type `Int -> Int`. See
the changes to the user manual for details.

This patch addresses tickets #10619, #5296, #10589.

Redundant constraints and defaulting warnings had "constraint(s)" in
their messages; the "s" is now conditional based on the number of things
warned about.

Reviewers: hvr, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1647

This implements the ideas originally put forward in
"System FC with Explicit Kind Equality" (ICFP'13).

There are several noteworthy changes with this patch:
 * We now have casts in types. These change the kind
   of a type. See new constructor `CastTy`.

 * All types and all constructors can be promoted.
   This includes GADT constructors. GADT pattern matches
   take place in type family equations. In Core,
   types can now be applied to coercions via the
   `CoercionTy` constructor.

 * Coercions can now be heterogeneous, relating types
   of different kinds. A coercion proving `t1 :: k1 ~ t2 :: k2`
   proves both that `t1` and `t2` are the same and also that
   `k1` and `k2` are the same.

 * The `Coercion` type has been significantly enhanced.
   The documentation in `docs/core-spec/core-spec.pdf` reflects
   the new reality.

 * The type of `*` is now `*`. No more `BOX`.

 * Users can write explicit kind variables in their code,
   anywhere they can write type variables. For backward compatibility,
   automatic inference of kind-variable binding is still permitted.

 * The new extension `TypeInType` turns on the new user-facing
   features.

 * Type families and synonyms are now promoted to kinds. This causes
   trouble with parsing `*`, leading to the somewhat awkward new
   `HsAppsTy` constructor for `HsType`. This is dispatched with in
   the renamer, where the kind `*` can be told apart from a
   type-level multiplication operator. Without `-XTypeInType` the
   old behavior persists. With `-XTypeInType`, you need to import
   `Data.Kind` to get `*`, also known as `Type`.

 * The kind-checking algorithms in TcHsType have been significantly
   rewritten to allow for enhanced kinds.

 * The new features are still quite experimental and may be in flux.

 * TODO: Several open tickets: #11195, #11196, #11197, #11198, #11203.

 * TODO: Update user manual.

Tickets addressed: #9017, #9173, #7961, #10524, #8566, #11142.
Updates Haddock submodule.

Checking for missing signatures before renaming the export list is
prone to errors, so we now perform the check in `reportUnusedNames` at
which point everything has been renamed.

Test Plan: validate, new test case is T10908

Reviewers: goldfire, simonpj, austin, bgamari

Subscribers: thomie

Projects: #ghc

Differential Revision: https://phabricator.haskell.org/D1561

GHC Trac Issues: #10908

HsImpExp.ieName is partial and fails when given e.g. `module X`

solution: use ieNames instead which returns a list of names instead of a single name.

Reviewed By: bgamari, austin

Differential Revision: https://phabricator.haskell.org/D1551

GHC Trac Issues: #11077

Warn about incoherent/non-canonical 'Applicative'/'Monad' instance
declarations. Specifically the following invariants are checked:

In 'Monad' instances declarations warn if the any of the following
conditions does not hold:

 * If `return` is overridden it must be canonical (i.e. `return = pure`).
 * If `(>>)` is overridden it must be canonical (i.e. `(>>) = (*>)`).

In 'Applicative' instance declarations:

 * Warn if 'pure' is defined backwards (i.e. `pure = return`).
 * Warn if '(*>)' is defined backwards (i.e. `(*>) = (>>)`).

NB, this warning flag is not enabled via `-Wall` nor `-Wcompat`.

This addresses #11128

Reviewers: quchen, austin, bgamari

Reviewed By: bgamari

Differential Revision: https://phabricator.haskell.org/D1516

The fix for Trac #10890 in commit 1818b48e, namely
   Fix incorrect import warnings when methods with identical names are imported
was wrong, as demonstrated by the new test T10890_2.  It suppressed
far too many warnings!

This patch fixes the original problem in a different way, by making
RdrName.greUsedRdrName a bit cleverer.

But this too is not really the Right Thing.  I think the Right Thing is
to store the /GRE/ in the tcg_used_rdrnames, not the /RdrName/.  That
would be a lot simpler and more direct.

But one step at a time.

Currently, GHC's warning generation code is assuming that a name (`RdrName`)
can be imported at most once. This is a correct assumption, because 1) it's OK
to import same names as long as we don't use any of them 2) when we use one of
them, GHC generates an error because it doesn't disambiguate it automatically.

But apparently the story is different with typeclass methods. If I import two
methods with same names, it's OK to use them in typeclass instance
declarations, because the context specifies which one to use. For example, this
is OK (where modules A and B define typeclasses A and B, both with a function
has),

    import A
    import B

    data Blah = Blah

    instance A Blah where
      has = Blah

    instance B Blah where
      has = Blah

But GHC's warning generator is not taking this into account, and so if I change
import list of this program to:

    import A (A (has))
    import B (B (has))

GHC is printing these warnings:

    Main.hs:5:1: Warning:
        The import of ‘A.has’ from module ‘A’ is redundant

    Main.hs:6:1: Warning:
        The import of ‘B.has’ from module ‘B’ is redundant

Why? Because warning generation code is _silently_ ignoring multiple symbols
with same names.

With this patch, GHC takes this into account. If there's only one name, then
this patch reduces to the previous version, that is, it works exactly the same
as current GHC (thanks goes to @quchen for realizing this).

Reviewed By: austin

Differential Revision: https://phabricator.haskell.org/D1257

GHC Trac Issues: #10890

Summary:
Instead of doing these warnings at MkIface time, we do them
when we create the instances/rules in the typechecker/desugarer.

Emitting warnings for auto-generated instances was a pain
(since the specialization monad doesn't have the capacity
to emit warnings) so instead I just deprecated -fwarn-auto-orphans.
Auto rule orphans are pretty harmless anyway: they don't cause
interface files to be eagerly loaded in.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, austin, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1297

Summary: Fixes T10637

Reviewers: austin, bgamari, thomie

Subscribers: dfordivam, simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1157

GHC Trac Issues: #10637

Noticed today that deprecation warnings are
slightly broken in -HEAD:

  mtl-2.2.1/Control/Monad/Error/Class.hs:46:1: warning:
    Module ‘Control.Monad.Trans.Error’ is deprecated:
      ([", U, s, e,  , C, o, n, t, r, o, l, ., M, o, n, a, d, ., T, r, a,
        n, s, ., E, x, c, e, p, t,  , i, n, s, t, e, a, d, "],
       Use Control.Monad.Trans.Except instead)

Commit e6191d1c
slightly changed WarningTxt declaration:

-data WarningTxt = WarningTxt (Located SourceText) [Located FastString]
-                | DeprecatedTxt (Located SourceText) [Located FastString]
+data WarningTxt = WarningTxt (Located SourceText)
+                             [Located (SourceText,FastString)]
+                | DeprecatedTxt (Located SourceText)
+                                [Located (SourceText,FastString)]

But 'moduleWarn' function was not updated to do the stripping.
Signed-off-by: Sergei Trofimovich <siarheit@google.com>

Reviewers: austin, bgamari, hvr, goldfire, rwbarton, alanz

Reviewed By: rwbarton, alanz

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1096

GHC Trac Issues: #10313

Reviewed By: nomeata, thomie

Differential Revision: https://phabricator.haskell.org/D760Signed-off-by: Dave Laing <dave.laing.80@gmail.com>

Summary: add `-fwarn-missing-exported-sigs` to only warn about missing signatures if the name is exported

Test Plan: validate, see testsuite/tests/warnings/should_compile/T2526.hs

Reviewers: ezyang, austin, thomie

Reviewed By: austin, thomie

Subscribers: ezyang, thomie, carter

Differential Revision: https://phabricator.haskell.org/D482

GHC Trac Issues: #2526

Conflicts:
	docs/users_guide/7.10.1-notes.xml

Summary:
This revision enables -fwarn-tabs by default and add a suppression
flag, so that GHC compilation won't fail when some files contain tab
characters.

Test Plan: Additional test case, T9230, was added to cover that change.

Reviewers: austin

Reviewed By: austin

Subscribers: simonmar, ezyang, carter, thomie, mlen

Differential Revision: https://phabricator.haskell.org/D255

GHC Trac Issues: #9230

Conflicts:
	testsuite/driver/testlib.py

Including a test case.

This matches GCC's choice of Unicode quotation marks (i.e. U+2018 and U+2019)
and therefore looks more familiar on the console. This addresses #2507.
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>