| Commit message (Collapse) | Author | Age | Files | Lines |
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This patch simplifies GHC to use simple subsumption.
Ticket #17775
Implements GHC proposal #287
https://github.com/ghc-proposals/ghc-proposals/blob/master/
proposals/0287-simplify-subsumption.rst
All the motivation is described there; I will not repeat it here.
The implementation payload:
* tcSubType and friends become noticably simpler, because it no
longer uses eta-expansion when checking subsumption.
* No deeplyInstantiate or deeplySkolemise
That in turn means that some tests fail, by design; they can all
be fixed by eta expansion. There is a list of such changes below.
Implementing the patch led me into a variety of sticky corners, so
the patch includes several othe changes, some quite significant:
* I made String wired-in, so that
"foo" :: String rather than
"foo" :: [Char]
This improves error messages, and fixes #15679
* The pattern match checker relies on knowing about in-scope equality
constraints, andd adds them to the desugarer's environment using
addTyCsDs. But the co_fn in a FunBind was missed, and for some reason
simple-subsumption ends up with dictionaries there. So I added a
call to addTyCsDs. This is really part of #18049.
* I moved the ic_telescope field out of Implication and into
ForAllSkol instead. This is a nice win; just expresses the code
much better.
* There was a bug in GHC.Tc.TyCl.Instance.tcDataFamInstHeader.
We called checkDataKindSig inside tc_kind_sig, /before/
solveEqualities and zonking. Obviously wrong, easily fixed.
* solveLocalEqualitiesX: there was a whole mess in here, around
failing fast enough. I discovered a bad latent bug where we
could successfully kind-check a type signature, and use it,
but have unsolved constraints that could fill in coercion
holes in that signature -- aargh.
It's all explained in Note [Failure in local type signatures]
in GHC.Tc.Solver. Much better now.
* I fixed a serious bug in anonymous type holes. IN
f :: Int -> (forall a. a -> _) -> Int
that "_" should be a unification variable at the /outer/
level; it cannot be instantiated to 'a'. This was plain
wrong. New fields mode_lvl and mode_holes in TcTyMode,
and auxiliary data type GHC.Tc.Gen.HsType.HoleMode.
This fixes #16292, but makes no progress towards the more
ambitious #16082
* I got sucked into an enormous refactoring of the reporting of
equality errors in GHC.Tc.Errors, especially in
mkEqErr1
mkTyVarEqErr
misMatchMsg
misMatchMsgOrCND
In particular, the very tricky mkExpectedActualMsg function
is gone.
It took me a full day. But the result is far easier to understand.
(Still not easy!) This led to various minor improvements in error
output, and an enormous number of test-case error wibbles.
One particular point: for occurs-check errors I now just say
Can't match 'a' against '[a]'
rather than using the intimidating language of "occurs check".
* Pretty-printing AbsBinds
Tests review
* Eta expansions
T11305: one eta expansion
T12082: one eta expansion (undefined)
T13585a: one eta expansion
T3102: one eta expansion
T3692: two eta expansions (tricky)
T2239: two eta expansions
T16473: one eta
determ004: two eta expansions (undefined)
annfail06: two eta (undefined)
T17923: four eta expansions (a strange program indeed!)
tcrun035: one eta expansion
* Ambiguity check at higher rank. Now that we have simple
subsumption, a type like
f :: (forall a. Eq a => Int) -> Int
is no longer ambiguous, because we could write
g :: (forall a. Eq a => Int) -> Int
g = f
and it'd typecheck just fine. But f's type is a bit
suspicious, and we might want to consider making the
ambiguity check do a check on each sub-term. Meanwhile,
these tests are accepted, whereas they were previously
rejected as ambiguous:
T7220a
T15438
T10503
T9222
* Some more interesting error message wibbles
T13381: Fine: one error (Int ~ Exp Int)
rather than two (Int ~ Exp Int, Exp Int ~ Int)
T9834: Small change in error (improvement)
T10619: Improved
T2414: Small change, due to order of unification, fine
T2534: A very simple case in which a change of unification order
means we get tow unsolved constraints instead of one
tc211: bizarre impredicative tests; just accept this for now
Updates Cabal and haddock submodules.
Metric Increase:
T12150
T12234
T5837
haddock.base
Metric Decrease:
haddock.compiler
haddock.Cabal
haddock.base
Merge note: This appears to break the
`UnliftedNewtypesDifficultUnification` test. It has been marked as
broken in the interest of merging.
(cherry picked from commit 66b7b195cb3dce93ed5078b80bf568efae904cc5)
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The big change here is to fix an outright bug in flattening of Givens,
albeit one that is very hard to exhibit. Suppose we have the constraint
forall a. (a ~ F b) => ..., (forall c. ....(F b)...) ...
Then
- we'll flatten the (F) b to a fsk, say (F b ~ fsk1)
- we'll rewrite the (F b) inside the inner implication to 'fsk1'
- when we leave the outer constraint we are suppose to unflatten;
but that fsk1 will still be there
- if we re-simplify the entire outer implication, we'll re-flatten
the Given (F b) to, say, (F b ~ fsk2)
Now we have two fsks standing for the same thing, and that is very
wrong.
Solution: make fsks behave more like fmvs:
- A flatten-skolem is now a MetaTyVar, whose MetaInfo is FlatSkolTv
- We "fill in" that meta-tyvar when leaving the implication
- The old FlatSkol form of TcTyVarDetails is gone completely
- We track the flatten-skolems for the current implication in
a new field of InertSet, inert_fsks.
See Note [The flattening story] in TcFlatten.
In doing this I found various other things to fix:
* I removed the zonkSimples from TcFlatten.unflattenWanteds; it wasn't
needed. But I added one in TcSimplify.floatEqualities, which does
the zonk precisely when it is needed.
* Trac #13674 showed up a case where we had
- an insoluble Given, e.g. a ~ [a]
- the same insoluble Wanted a ~ [a]
We don't use the Given to rewwrite the Wanted (obviously), but
we therefore ended up reporting
Can't deduce (a ~ [a]) from (a ~ [a])
which is silly.
Conclusion: when reporting errors, make the occurs check "win"
See Note [Occurs check wins] in TcErrors
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This major commit was initially triggered by #11339, but it spiraled
into a major review of the way in which type signatures for bindings
are handled, especially partial type signatures. On the way I fixed a
number of other bugs, namely
#12069
#12033
#11700
#11339
#11670
The main change is that I completely reorganised the way in which type
signatures in bindings are handled. The new story is in TcSigs
Note [Overview of type signatures]. Some specific:
* Changes in the data types for signatures in TcRnTypes:
TcIdSigInfo and new TcIdSigInst
* New module TcSigs deals with typechecking type signatures
and pragmas. It contains code mostly moved from TcBinds,
which is already too big
* HsTypes: I swapped the nesting of HsWildCardBndrs
and HsImplicitBndsrs, so that the wildcards are on the
oustide not the insidde in a LHsSigWcType. This is just
a matter of convenient, nothing deep.
There are a host of other changes as knock-on effects, and
it all took FAR longer than I anticipated :-). But it is
a significant improvement, I think.
Lots of error messages changed slightly, some just variants but
some modest improvements.
New tests
* typecheck/should_compile
* SigTyVars: a scoped-tyvar test
* ExPat, ExPatFail: existential pattern bindings
* T12069
* T11700
* T11339
* partial-sigs/should_compile
* T12033
* T11339a
* T11670
One thing to check:
* Small change to output from ghc-api/landmines.
Need to check with Alan Zimmerman
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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.
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This patch began as a modest refactoring of HsType and friends, to
clarify and tidy up exactly where quantification takes place in types.
Although initially driven by making the implementation of wildcards more
tidy (and fixing a number of bugs), I gradually got drawn into a pretty
big process, which I've been doing on and off for quite a long time.
There is one compiler performance regression as a result of all
this, in perf/compiler/T3064. I still need to look into that.
* The principal driving change is described in Note [HsType binders]
in HsType. Well worth reading!
* Those data type changes drive almost everything else. In particular
we now statically know where
(a) implicit quantification only (LHsSigType),
e.g. in instance declaratios and SPECIALISE signatures
(b) implicit quantification and wildcards (LHsSigWcType)
can appear, e.g. in function type signatures
* As part of this change, HsForAllTy is (a) simplified (no wildcards)
and (b) split into HsForAllTy and HsQualTy. The two contructors
appear when and only when the correponding user-level construct
appears. Again see Note [HsType binders].
HsExplicitFlag disappears altogether.
* Other simplifications
- ExprWithTySig no longer needs an ExprWithTySigOut variant
- TypeSig no longer needs a PostRn name [name] field
for wildcards
- PatSynSig records a LHsSigType rather than the decomposed
pieces
- The mysterious 'GenericSig' is now 'ClassOpSig'
* Renamed LHsTyVarBndrs to LHsQTyVars
* There are some uninteresting knock-on changes in Haddock,
because of the HsSyn changes
I also did a bunch of loosely-related changes:
* We already had type synonyms CoercionN/CoercionR for nominal and
representational coercions. I've added similar treatment for
TcCoercionN/TcCoercionR
mkWpCastN/mkWpCastN
All just type synonyms but jolly useful.
* I record-ised ForeignImport and ForeignExport
* I improved the (poor) fix to Trac #10896, by making
TcTyClsDecls.checkValidTyCl recover from errors, but adding a
harmless, abstract TyCon to the envt if so.
* I did some significant refactoring in RnEnv.lookupSubBndrOcc,
for reasons that I have (embarrassingly) now totally forgotten.
It had to do with something to do with import and export
Updates haddock submodule.
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This puts the "Relevant bindings" section at the end.
It uses a TcErrors.Report Monoid to divide messages by importance and
then mappends them together. This is not the most efficient way since
there are various intermediate Reports and list appends, but it probably
doesn't matter since error messages shouldn't get that large, and are
usually prepended. In practice, everything is `important` except
`relevantBindings`, which is `supplementary`.
ErrMsg's errMsgShortDoc and errMsgExtraInfo were extracted into ErrDoc,
which has important, context, and suppelementary fields. Each of those
three sections is marked with a bullet character, '•' on unicode
terminals and '*' on ascii terminals. Since this breaks tons of tests,
I also modified testlib.normalise_errmsg to strip out '•'s.
--- Additional notes:
To avoid prepending * to an empty doc, I needed to filter empty docs.
This seemed less error-prone than trying to modify everyone who produces
SDoc to instead produce Maybe SDoc. So I added `Outputable.isEmpty`.
Unfortunately it needs a DynFlags, which is kind of bogus, but otherwise
I think I'd need another Empty case for SDoc, and then it couldn't be a
newtype any more.
ErrMsg's errMsgShortString is only used by the Show instance, which is
in turn only used by Show HscTypes.SourceError, which is in turn only
needed for the Exception instance. So it's probably possible to get rid
of errMsgShortString, but that would a be an unrelated cleanup.
Fixes #11014.
Test Plan: see above
Reviewers: austin, simonpj, thomie, bgamari
Reviewed By: thomie, bgamari
Subscribers: simonpj, nomeata, thomie
Differential Revision: https://phabricator.haskell.org/D1427
GHC Trac Issues: #11014
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In particular
In the type signature for:
f :: Int -> Int
I added the colon
Also reword the "maybe you haven't applied a function to enough arguments?"
suggestion to make grammatical sense.
These tiny changes affect a lot of error messages.
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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>
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Almost all are re-orderings of relevant-binding output
Relevant bindings include
+ m :: Map (a, b) elt (bound at T3169.hs:12:17)
+ b :: b (bound at T3169.hs:12:13)
lookup :: (a, b) -> Map (a, b) elt -> Maybe elt
(bound at T3169.hs:12:3)
- b :: b (bound at T3169.hs:12:13)
- m :: Map (a, b) elt (bound at T3169.hs:12:17)
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In effect, the error context for naked variables now takes up
a "slot" in the context stack; but it is often empty. So the
context stack becomes one shorter in those cases. I don't think
this matters; indeed, it's aguably an improvement. Anyway that's
why so many tests are affected.
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Notably
* Showing relevant bindings
* Not suggesting add instance (Num T); see Trac #7222
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major TcErrors refactoring
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