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I've changed the name from `Valid substitutions` to `Valid hole fits`,
since "substitution" already has a well defined meaning within the
theory. As part of this change, the flags and output is reanamed, with
substitution turning into hole-fit in most cases. "hole fit" was already
used internally in the code, it's clear and shouldn't cause any
confusion.
In this update, I've also reworked how we manage side-effects in the
hole we are considering.
This allows us to consider local bindings such as where clauses and
arguments to functions, suggesting e.g. `a` for `head (x:xs) where head
:: [a] -> a`.
It also allows us to find suggestions such as `maximum` for holes of
type `Ord a => a -> [a]`, and `max` when looking for a match for the
hole in `g = foldl1 _`, where `g :: Ord a => [a] -> a`.
We also show much improved output for refinement hole fits, and
fixes #14990. We now show the correct type of the function, but we also
now show what the arguments to the function should be e.g. `foldl1 (_ ::
Integer -> Integer -> Integer)` when looking for `[Integer] -> Integer`.
I've moved the bulk of the code from `TcErrors.hs` to a new file,
`TcHoleErrors.hs`, since it was getting too big to not live on it's own.
This addresses the considerations raised in #14969, and takes proper
care to set the `tcLevel` of the variables to the right level before
passing it to the simplifier.
We now also zonk the suggestions properly, which improves the output of
the refinement hole fits considerably.
This also filters out suggestions from the `GHC.Err` module, since even
though `error` and `undefined` are indeed valid hole fits, they are
"trivial", and almost never useful to the user.
We now find the hole fits using the proper manner, namely by solving
nested implications. This entails that the givens are passed along using
the implications the hole was nested in, which in turn should mean that
there will be fewer weird bugs in the typed holes.
I've also added a new sorting method (as suggested by SPJ) and sort by
the size of the types needed to turn the hole fits into the type of the
hole. This gives a reasonable approximation to relevance, and is much
faster than the subsumption check. I've also added a flag to toggle
whether to use this new sorting algorithm (as is done by default) or the
subsumption algorithm. This fixes #14969
I've also added documentation for these new flags and update the
documentation according to the new output.
Reviewers: bgamari, goldfire
Reviewed By: bgamari
Subscribers: simonpj, rwbarton, thomie, carter
GHC Trac Issues: #14969, #14990, #10946
Differential Revision: https://phabricator.haskell.org/D4444
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The main job of this commit is to track more accurately the scope
of tyvars introduced by user-written foralls. For example, it would
be to have something like this:
forall a. Int -> (forall k (b :: k). Proxy '[a, b]) -> Bool
In that type, a's kind must be k, but k isn't in scope. We had a
terrible way of doing this before (not worth repeating or describing
here, but see the old tcImplicitTKBndrs and friends), but now
we have a principled approach: make an Implication when kind-checking
a forall. Doing so then hooks into the existing machinery for
preventing skolem-escape, performing floating, etc. This also means
that we bump the TcLevel whenever going into a forall.
The new behavior is done in TcHsType.scopeTyVars, but see also
TcHsType.tc{Im,Ex}plicitTKBndrs, which have undergone significant
rewriting. There are several Notes near there to guide you. Of
particular interest there is that Implication constraints can now
have skolems that are out of order; this situation is reported in
TcErrors.
A major consequence of this is a slightly tweaked process for type-
checking type declarations. The new Note [Use SigTvs in kind-checking
pass] in TcTyClsDecls lays it out.
The error message for dependent/should_fail/TypeSkolEscape has become
noticeably worse. However, this is because the code in TcErrors goes to
some length to preserve pre-8.0 error messages for kind errors. It's time
to rip off that plaster and get rid of much of the kind-error-specific
error messages. I tried this, and doing so led to a lovely error message
for TypeSkolEscape. So: I'm accepting the error message quality regression
for now, but will open up a new ticket to fix it, along with a larger
error-message improvement I've been pondering. This applies also to
dependent/should_fail/{BadTelescope2,T14066,T14066e}, polykinds/T11142.
Other minor changes:
- isUnliftedTypeKind didn't look for tuples and sums. It does now.
- check_type used check_arg_type on both sides of an AppTy. But the left
side of an AppTy isn't an arg, and this was causing a bad error message.
I've changed it to use check_type on the left-hand side.
- Some refactoring around when we print (TYPE blah) in error messages.
The changes decrease the times when we do so, to good effect.
Of course, this is still all controlled by
-fprint-explicit-runtime-reps
Fixes #14066 #14749
Test cases: dependent/should_compile/{T14066a,T14749},
dependent/should_fail/T14066{,c,d,e,f,g,h}
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This builds on the previous "Valid substitutions include..." functionality,
but add subsumption checking as well, so that the suggested valid substitutions
show not only exact matches, but also identifiers that fit the hole by virtue of
subsuming the type of the hole (i.e. being more general than the type of the
hole).
Building on the previous example, in the given program
```
ps :: String -> IO ()
ps = putStrLn
ps2 :: a -> IO ()
ps2 _ = putStrLn "hello, world"
main :: IO ()
main = _ "hello, world"
```
The results would be something like
```
• Found hole: _ :: [Char] -> IO ()
• In the expression: _
In the expression: _ "hello, world"
In an equation for ‘main’: main = _ "hello, world"
• Relevant bindings include main :: IO () (bound at t1.hs:8:1)
Valid substitutions include
ps :: String -> IO () (defined at t1.hs:2:1)
ps2 :: forall a. a -> IO () (defined at t1.hs:5:1)
putStrLn :: String -> IO ()
(imported from ‘Prelude’ at t1.hs:1:1
(and originally defined in ‘System.IO’))
fail :: forall (m :: * -> *). Monad m => forall a. String -> m a
(imported from ‘Prelude’ at t1.hs:1:1
(and originally defined in ‘GHC.Base’))
mempty :: forall a. Monoid a => a
(imported from ‘Prelude’ at t1.hs:1:1
(and originally defined in ‘GHC.Base’))
print :: forall a. Show a => a -> IO ()
(imported from ‘Prelude’ at t1.hs:1:1
(and originally defined in ‘System.IO’))
(Some substitutions suppressed;
use -fmax-valid-substitutions=N or -fno-max-valid-substitutions)
```
Signed-off-by: Matthías Páll Gissurarson <mpg@mpg.is>
Modified according to suggestions from Simon PJ
Accept tests that match the expectations, still a few to look better at
Swithced to using tcLookup, after sit down with SPJ at ICFP. Implications are WIP.
Now works with polymorphism and constraints!
We still need to merge the latest master, before we can make a patch.
Wrap the type of the hole, instead of implication shenanigans,
As per SPJs suggestion, this is simpler and feels closer to
what we actually want to do.
Updated tests with the new implementation
Remove debugging trace and update documentation
Reviewers: austin, bgamari
Reviewed By: bgamari
Subscribers: RyanGlScott, rwbarton, thomie
Differential Revision: https://phabricator.haskell.org/D3930
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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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varSetElemsWellScoped introduces unnecessary non-determinism in
inferred type signatures.
Removing this instance required changing the representation of
TcDepVars to use deterministic sets.
This is the last occurence of varSetElemsWellScoped, allowing me to
finally remove it.
Test Plan:
./validate
I will update the expected outputs when commiting, some reordering
of type variables in types is expected.
Reviewers: goldfire, simonpj, austin, bgamari
Reviewed By: simonpj
Subscribers: thomie, simonmar
Differential Revision: https://phabricator.haskell.org/D2135
GHC Trac Issues: #4012
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The idea here is described in [wiki:Typechecker]. Briefly,
this refactor keeps solid track of "synthesis" mode vs
"checking" in GHC's bidirectional type-checking algorithm.
When in synthesis mode, the expected type is just an IORef
to write to.
In addition, this patch does a significant reworking of
RebindableSyntax, allowing much more freedom in the types
of the rebindable operators. For example, we can now have
`negate :: Int -> Bool` and
`(>>=) :: m a -> (forall x. a x -> m b) -> m b`. The magic
is in tcSyntaxOp.
This addresses tickets #11397, #11452, and #11458.
Tests:
typecheck/should_compile/{RebindHR,RebindNegate,T11397,T11458}
th/T11452
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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.
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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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The patch "Treat out-of-scope variables as holes" makes
lots of error messages change a bit. This patch has all
the change.
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This regrettably-big patch substantially improves the way in which
"improvement" happens in the constraint solver. It was triggered by
trying to crack Trac #10009, but it turned out to solve #10340 as
well.
The big picture, with several of the trickiest examples, is described
in Note [The improvement story] in TcInteract.
The major change is this:
* After solving we explicitly try "improvement", by
- making the unsolved Wanteds into Deriveds
- allowing Deriveds to rewrite Deriveds
This more aggressive rewriting "unlocks" some extra
guess-free unifications.
* The main loop is in TcInteract.solveSimpleWanteds, but I also ended
up refactoring TcSimplify.simpl_loop, and its surrounding code.
Notably, any insolubles from the Givens are pulled out
and treated separately, rather than staying in the inert set
during the solveSimpleWanteds loop.
There are a lot of follow-on changes
* Do not emit generate Derived improvements from Wanteds.
This saves work in the common case where they aren't needed.
* For improvement we should really do type-class reduction on Derived
constraints in doTopReactDict. That entailed changing the GenInst
constructor a bit; a local and minor change
* Some annoying faffing about with dropping derived constraints;
see dropDerivedWC, dropDerivedSimples, dropDerivedInsols,
and their Notes.
* Some substantial refactoring in TcErrors.reportWanteds.
This work wasn't strictly forced, but I got sucked into it.
All the changes are in TcErrors.
* Use TcS.unifyTyVar consistently, rather than setWantedTyBind,
so that unifications are properly tracked.
* Refactoring around solveWantedsTcM, solveWantedsAndDrop.
They previously guaranteed a zonked result, but it's more
straightforward for clients to zonk.
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The idea was promted by Trac #9939, but it was Christmas, so I did
some recreational programming that went much further.
The idea is to warn when a constraint in a user-supplied context is
redundant. Everything is described in detail in
Note [Tracking redundant constraints]
in TcSimplify.
Main changes:
* The new ic_status field in an implication, of type ImplicStatus.
It replaces ic_insol, and includes information about redundant
constraints.
* New function TcSimplify.setImplicationStatus sets the ic_status.
* TcSigInfo has sig_report_redundant field to say whenther a
redundant constraint should be reported; and similarly
the FunSigCtxt constructor of UserTypeCtxt
* EvBinds has a field eb_is_given, to record whether it is a given
or wanted binding. Some consequential chagnes to creating an evidence
binding (so that we record whether it is given or wanted).
* AbsBinds field abs_ev_binds is now a *list* of TcEvBiinds;
see Note [Typechecking plan for instance declarations] in
TcInstDcls
* Some significant changes to the type checking of instance
declarations; Note [Typechecking plan for instance declarations]
in TcInstDcls.
* I found that TcErrors.relevantBindings was failing to zonk the
origin of the constraint it was looking at, and hence failing to
find some relevant bindings. Easy to fix, and orthogonal to
everything else, but hard to disentangle.
Some minor refactorig:
* TcMType.newSimpleWanteds moves to Inst, renamed as newWanteds
* TcClassDcl and TcInstDcls now have their own code for typechecking
a method body, rather than sharing a single function. The shared
function (ws TcClassDcl.tcInstanceMethodBody) didn't have much code
and the differences were growing confusing.
* Add new function TcRnMonad.pushLevelAndCaptureConstraints, and
use it
* Add new function Bag.catBagMaybes, and use it in TcSimplify
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Summary:
As proposed by Richard on Trac. This patch adds a new flag -fdefer-typed-holes
and changes the semantics of the -fno-warn-typed-holes flag.
To summarise, by default GHC has typed holes enabled and produces a compile
error when it encounters a typed hole.
When -fdefer-type-errors OR -fdefer-typed-holes is enabled, hole errors are
converted to warnings and result in runtime errors when evaluated.
The warning flag -fwarn-typed-holes is on by default. Without -fdefer-type-errors
or -fdefer-typed-holes this flag is a no-op, since typed holes are an error
under these conditions. If either of the defer flags are enabled (converting
typed hole errors into warnings) the -fno-warn-typed-holes flag disables the
warnings. This means compilation silently succeeds and evaluating a hole will
produce a runtime error.
The rationale behind allowing typed holes warnings to be silenced is that tools
like Syntastic for vim highlight warnings and hole warnings may be undesirable.
Signed-off-by: Merijn Verstraaten <merijn@inconsistent.nl>
Test Plan: validate
Reviewers: austin, simonpj, thomie
Reviewed By: simonpj, thomie
Subscribers: Fuuzetsu, thomie, carter
Differential Revision: https://phabricator.haskell.org/D442
GHC Trac Issues: #9497
Conflicts:
compiler/main/DynFlags.hs
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After some discussion on ghc-devs@ and elsewhere, it seemed favorable to
make this change as type holes don't let any invalid programs though,
they merely change what the compiler reports in case of certain errors
(namely unbound occurrences, or _ appearing on a LHS.)
Now, the warning mechanism is controlled by -f[no-]warn-type-errors,
just like any other regular warning. Again, on by default.
The documentation and tests have been updated accordingly.
Signed-off-by: Austin Seipp <austin@well-typed.com>
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